159
SYNTHESIS AND CHARECTERIZATION OF AUTOCHTHONIC GUAR GUM DERIVATIVES DEPARTMENT OF CHEMISTRY LAHORE COLLEGE FOR WOMEN UNIVERISTY, LAHORE, PAKISTAN 2013
SYNTHESIS AND CHARECTERIZATION OF
AUTOCHTHONIC GUAR GUM DERIVATIVES
DEPARTMENT OF CHEMISTRY
LAHORE COLLEGE FOR WOMEN UNIVERISTY, LAHORE,
PAKISTAN
2013
SYNTHESIS AND CHARECTERIZATION OF
AUTOCHTHONIC GUAR GUM DERIVATIVES
A THESIS SUBMITTED TO
LAHORE COLLEGE FOR WOMEN UNIVERISTY, LAHORE
IN THE PARTIAL FULLFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF
DOCTOR OF PHILOSOPHY
IN CHEMISTRY
By
DURE NAJAF IQBAL
DEPARTMENT OF CHEMISTRY
LAHORE COLLEGE FOR WOMEN UNIVERISTY, LAHORE,
PAKISTAN
2013
i
CERTIFICATE
It is certified that the thesis entitled ‘‘Synthesis and characterization of autochthonic guar
gum derivatives’’ submitted by Ms dure najaf iqbal to the Department of chemistry, Lahore
College for Women University Lahore, Pakistan is her own work and is not submitted
previously , in whole or in parts , in respect of any other academic award.
____________________ ___________________
Signature of Candidate Date
I approved the above thesis to be submitted for the examination.
____________________ ____________________
Signature of Supervisor Chairperson
Department of Chemistry
ii
DECLARATION
I declare that the work in this dissertation was carried out in accordance with the
Regulations of the Lahore College for Women University, Lahore. The work is original,
except where indicated by special reference in the text, and no part of the dissertation has
been submitted for any other academic award. Any views expressed in the dissertation are
those of the author.
Signature of Candidate ____________ _________________ Date
iii
I DEDICATE THIS THESIS TO MY HUSBAND,
MR AMMIR MUNIR
WHO HAS BEEN A CONSTANT SOURCE OF ENCOURAGEMENT AND
SUPPORT DURING THE CHALLENGES OF MY Ph.D. STUDY
iv
ACKNOWLEDGEMENT
In the name of Allah, the Most Gracious and the Most Merciful
First of all, I thank Allah (SWT) for bestowing me with His countless blessings and
enabled me to complete this dissertation successfully. Also, I cannot forget the ideal man
of the world and most respectable personality for whom Allah has created the whole
universe, Prophet Mohammed (Peace Be upon Him).
This thesis would not have been completed without the help, support, guidance, and
efforts of many people. I would like to acknowledge all those who gave me the
encouragement to complete this thesis. I wish to express my sincere gratitude and
appreciations to my supervisor Dr Erum Akbar, for her professional and unwavering
dedication in the course of instructing my PhD training. She had supported me at all
levels of my training and her kindness, guidance, and encouragement helped me to going
through the difficulties and crises I met during the path of this work.
I highly appreciate Prof. Dr. Bushra Khan, Head of the Chemistry Department and prof.
Dr. Kausar Jamal Cheeme, Dean of Sciences, Lahore College for Women University for
facilitating us and providing us an adorable and productive environment for research. I
also wish to thanks Prof. Dr. Rahskhanda Nawaz, Her personal academic support
stimulates every student for learning.
I am immensely pleased to place on record my profound gratitude and thanks to Prof
Chris Wills (supervisor during my visit in University of Bristol, UK) .I have acquired a
multitude of research skills (in diverse areas of organic chemistry), academic writing
skills, presentation skills and novel synthetic techniques . I have noted with deep level of
appreciations and thanks for all you have done to me. My gratitude to Dr. Craig Butts,
for the training in all aspects of NMR structure determination. I appreciate your patience
in containing our mistakes in handling the NMR spectrometers. My thanks also to the
other NMR staff: Paul Lawrence and Rose Sylvester. I am grateful to Dr Song, Ms Zahida
wasi ,Ms Iman Ganam for their useful advices. Thanks for all loving people in Bristol
specially Mr. Arif and family. The memories of Bristol will remain with me forever.
v
I am obliged to the following Ph.D. fellows Asma, Nosheen, Lubna, Abida, Nazia,
Sumera, Alya, and Zeb for the good time we have spent as PhDcolleagues. I thank all the
remaining past and present members of Dr Erum Akbar group for their support and
friendship.Special thanks to my friend Faiza Hassan. I am extremely honoured to have
been able to share friendship, anxiety and the joy of the Ph.D. studies with you during the
last five years. I have no words to express how grateful I am for your help and how much
I have enjoyed our discussions about scientific and, to be honest, quite often unscientific
topics.
I will not forget the assistance of a number of supporting staff of the Chemistry
department laboratory and library .I am equally grateful to all faculty members of
department for their suggestions and critical comments. Special thanks to Dr Narjis Naz,
Your professional input has always and tremendously contributed in shaping my work.
I appreciate the unflinching moral support, patience and love of my Husband, Mr. Aamir
Munir and my children Ayesha aamir and Abdurrahman throughout the period of my
studies. You people are amazing and very, very dear to me. I am truly grateful to my
parents and parents in law for support, prayers, and best wishes. I ever remain grateful to
my sister in law Appi Qamar and family for looking after my kids when I was busy in my
study. I am forever indebted to all of my family members my sisters Shaheena, Erum,
Rizwana, kiran and brothers Usman, Salman and irfan kisana for their patience and
encouragement at each and every step of my study.
I was fortunate to receive a scholarship from Higher Education Commission Pakistan to
pursue my PhD. I would like to appreciate and thank HEC Pakistan for their financial
support under scholarship scheme indigenous 5000 Fellowship program and International
Research Support Initiative Program to achieve my goal.
Dure Najaf Iqbal
vi
ABBRIVIATIONS
AFM Atomic force microscopy
Ar Aromatic
Ba(OH)2 Barium hydroxide
CMG Carboxymethyl guar
CNTs Carbon nanotubes
CHPTAC
3-chloro-2-hydroxypropyltrimethyl
ammonium chloride
CHPDLAC 3-chloro-2-hydroxypropyldimethyl
Dodecyl ammonium chloride
CHPCDAC
3-chloro-2-
hydroxypropylcocoalkyldimethyl
ammonium chloride
CHPDSAC
3-chloro-2-hydroxypropyldimethyl
Stearyl ammonium chloride
Cr (VI) Hexavalent Chromium
D2O deuterium oxide
DCl deuterium chloride
DCC N,N-Dicyclohexylcarbodiimide
DMF Dimethylformamide
DMSO Dimethyl sulfoxide
DMS Dimethyl sulfide
DMAP 4-Dimethylaminopyridine
DPPH 2,2-Diphenyl-1-picrylhydrazyl
DSC Differential scanning calorimetry
DS Degree of substitution
ETA 2,3-epoxypropyltrimethylammonium
chloride
FTIR Fourier Transform InfraRed
GGAc Guar Acetate
GGBu Guar Butyrate
vii
GGC Guar gum cinnamate
GGCa Guar gum Caffeate
GG-cap Guar gum Caprates/ Decanoates
GG-oct Guar gum Caprylate /Octanoate
GGCit Guar Citraconate
GGCo Guar gum Coumarate
GGH Guar gum hydrocinnmate
GGF Guar gum ferulate
GGGl Guar Glutarate
GG-Hex Guar gum Hexanoate
GG-Hep Guar gum Heptanoate
GG-Lau Guar gum Lauroate
GGMal Guar Maleate
GG-Myr Guar gum Myristate
GG-Pht Guar Phthalate
GGPr Guar Propionate
GG-Pal Guar Palmitate
GG-Pel Guar gum Pelargonates
GG-ste Guar gum Stearate
GGSuc Guar Succinate
GG-Val Guar Valerate
GPC Gel permeation chromatography
GMA Glycidyl methyl methacrylate
HCl Hydrochloric acid
HEG Hydroxy ethyl guar
HNO3 Nitric acid
HPG Hydroxypropyl guar
HZ Hertz (NMR)
J Coupling constant
KOH Potasium hydroxide
KBr Potassium bromide
MMA Methyl Methacrylate
MI Methyl iodide
viii
NaHCO3 Sodium bicarbonate
NaOH Sodium Hydroxide
Py Pyridine
NMR Nuclear Magnetic Resonance
PNIPAAm Poly (N-isopropylacrylamide)
PEGDGE polyethylene glycol diglycidylether
ppm Parts per million
THEOS tetrakis (2 hydroxyethyl) orthosilicates
TGA/DTA Thermogravimetric Analysis/ Differential
Thermal Analysis
TLC Thin layer chromatography
SEM Scanning electron Microscopy
SGG Sulfated guar gum
TEM Transmission electron microscopy
UV Ultraviolet
XRD X-ray diffraction
ix
ABSTRACT
The objective of this research is to introduce new green, nontoxic, cost effective
derivatives of guar gum (GG-1). Guar gum is one of the important naturally occurring
non-ionic polysaccharide which has incredible applications due to its rheological
modifying properties in medicinal, pharmaceutical, food, textile, cosmetics, water
treatment, mining, drilling, explosives, confectioneries and scores of other industrial and
commercial sectors. Guar gum, also called guaran, is a galactomannan. It is primarily the
ground endosperm of guar beans. The guar seeds are dehusked, milled and screened to
obtain the guar gum. It is typically produced as a free-flowing, off-white powder.The
adaptation of physical properties of GG-1 & GG-2 can improve and diversify its
commercial applications.
GUAR GUM
x
In this project, novel and efficient synthesis of five different new derivatives (120-124) of
guar gum were done by insitu activation of cinnamic acid, ferulic acid, caffeic acid,
coumaric acid and hydrocinnamic acid by coupling with dicyclohexylcarbodiimide
(DCC) and N, N-dimethylaminopyridine (DMAP). Effect of temperature, concentration
of reactants and time interval plays important role for determining DS value of guar
esters. Reaction conditions were optimized for each reaction. Antioxidant potential was
examined by DPPH method.
A rapid method for protecting the hydroxyl group in sterically hindered gum has been
developed by using microwave assisted synthesis (MAS). A novel and efficient synthesis
of different guar gum derivatives (126-133) such as acetate, butyrate propionate, maleate,
succinate, phthalate, citraconate and glutarate have been developed by microwave
irradiation. The maximum ester formation was successfully achieved in 15minutes at
600W by using iodine and DMAP as a reaction promoter. Gum ester formation was
obtained by concentration variation at different time intervals. The products were
characterized by IR and NMR spectroscopy and SEM. Moreover, degree of substitution
was also calculated for each experiment by titration method.
First time fatty acid esters (C5-C18) were formulated (136-145) via acid chloride route.
Reaction proceeded in two steps. First step involves conventional synthesis of fatty acid
chlorides (135a-135j) by reacting corresponding acid with slight excess of thionyl
chloride (134). Second step involves esterification of free hydroxyl group of GG-2 with
acid chloride; as a result novel derivatives (136-145) with fascinating thickening and
emulsifying properties were obtained which might be promising candidate for cosmetic
and food industry.
Physical properties were examined like solubility, surface morphological study, swelling
behavior, gelation index etc. Different spectroscopic techniques were used for structure
elucidation. In situ hydrolysis of guar esters were done in DCl during NMR experiments
due to the poor solubility of guar derivatives. Guar derivatives with variable degree of
substitution (DS) were prepared and were confirmed by FT-IR spectroscopy, presence of
carbonyl signal confirmed the formation of guar ester. Further structural elucidation was
done by 1H-NMR .Surface morphological study of guar esters was done by scanning
electron microscopy (SEM) which showed networking in guar derivatives which
xi
enhanced when degree of substitution increased. Degree of substitution was determined
quantitatively by titration method for each derivative.
OORO O
O
O
O
OH
OORO O
O
O
O
OH
OORO O
O
OH
OO
OORO
OR
O
O
O
O
OH
OORO
OR
O
O
O O
OH
OROR
OR
129
130131
132133
OOHO O
OH
OH
GG-2
MW
MW
MW
MW
MW
125E
125D
125F
125G
125HDMAP
DMAP
DMAP
DMAP
DMAP
Some Synthetic guar gum derivatives
xii
TABLE OF CONTENTS
Description
Page No
Certificate i
Declaration ii
Dedication iii
Acknowledgement iv
Abbreviations vi
Abstract ix
List of figures xvii
List of Tables xviii
List of schemes xx
Chapter 1 Introduction
1.1 Preamble 2
1.2 Guar Gum 3
1.2.1 Chemical Structure, Properties of guar gum 5
1.2.2 Applications of guar gum 7
1.3 Aims and Objectives
10
Chapter 2 Literature Review
2.1 Cationic guar gum 13
2.2 Grafted Guar Gum 16
2.3 Guar gum ethers 22
2.3.1 Methylated guar 22
2.3.2 Carboxymethylated guar 23
2.3.3 Sulfated guar gum 25
2.3.3 Hydroxyalkylated guar gum 26
2.4 Guar gum esters 28
xiii
Chapter 3
Experimental
3.1 Materials 32
3.2 Measurements 32
3.3 Methods 33
3.3.1 Purification of guar gum
33
SECTION I
3.4 Guar gum Derivatives with Antioxidant Moieties by in
situ activation of phenolic acid
33
3.4.1 Synthesis of guar gum cinnamate-GGC (120) 34
3.4.2 Synthesis of guar gum ferulate GGF (121) 35
3.4.3 Synthesis of guar gum Caffeate–GGCa (122) 36
3.4.4 Synthesis of guar gum Coumarate –GGCo (123) 37
3.4.5 Synthesis of guar gum hydrocinnmate-GGH (124) 38
3.4.6 Determination of degree of substitution (DS) by
Wurzburg titration method
39
3.4.7 Antioxidant potential 40
SECTION II
3.5
Microwave assisted synthesis of guar gum derivatives via
Acid anhydride
41
3.5.1 A Synthesis of 126, 127, 128 (Method A) 41
3.5.1 B Synthesis of Guar Derivatives (129-133) via
cyclic anhydrides (Method B)
41
3.5.2 Synthesis of Guar Acetate-GGAc (126) 42
3.5.3 Synthesis of Guar Propionate-GG-Pr (127) 43
3.5.4 Synthesis of Guar Butyrate- GGBu (128) 43
3.5.5 Synthesis of Guar Succinate-GGSuc (129) 44
xiv
3.5.6 Synthesis of Guar Maleate-GGMal (130) 45
3.5.7 Synthesis of Guar Phthalate- GG-Pht (131) 45
3.5.8 Synthesis of Guar Citraconate-GGCit (132) 46
3.5.9 Synthesis of Guar Glutarate–GGGl (133) 47
3.5.10 Quantitative Measurement of Degree of
substitution of guar esters
48
SECTION III
3.6 Heterogeneous Esterification of guar gum via fatty
acid chloride
49
3.6.1 Synthesis of guar Valerate-GG-Val (136) 50
3.6.2 Synthesis of guar caproate/Hexanoate-
GG-Hex (137)
51
3.6.3 Synthesis of guar gum Heptanoate –
GG-Hep (138)
52
3.6.4 Synthesis of Guar gum Caprylate /Octanoate –
GG- oct (139)
53
3.6.5 Synthesis of Guar gum Pelargonates –
GG-Pel (140)
54
3.6.6 Synthesis of Guar gum Caprates/ Decanoates
-GG-cap (141)
55
3.6.7 Synthesis of Guar Gum Lauroate -GG-Lau (142) 56
3.6.8 Synthesis of guar gum Myristate-GG-Myr (143) 57
3.6.9 Synthesis of Guar Palmitate-GG-Pal (144) 58
3.6.10 Synthesis of guar gum Stearate -GG-ste (145) 59
3.7 Determination of Degree of Substitution by, Heinze,
Philipp, Klemm And Wagenknecht (1998) Method
60
SECTION IV
3.8 Testing Of Guar Gum Derivatives 61
xv
3.8.1 Determination of Solubilities 61
3.8.2 Water Holding Capacity /Swelling Ratio of guar
gum derivatives
61
3.8.3 Gelation Study 62
Chapter 4 Results and Discussion
SECTION I
4.1 Novel Derivatives of Guar with Antioxidant Moieties 64
4.1.1 Conversion of GG-1 via cinnamic acid 118a 68
4.1.2 Conversion of GG-1 via trans-Ferulic acid 118b 69
4.1.3 Conversion of GG-1 via Caffeic acid 118c 69
4.1.4 Conversion of GG-1 via p-Coumaric acid 118d 70
4.1.5 Conversion of GG-1 via Hydrocinnamic acid
118e
70
4.1.6 Antioxidant Assay of Guar Derivatives 120-124 71
4.1.7 DPPH Assay 71
4.1.8 Radical Scavenging studies of DPPH
72
SECTION II
4.2
Novel Route for modification of guar gum by microwave
irradiation
75
4.2.1 Acetylation of GG-2 78
4.2.2 Guar propionate (127) and guar butyrate (128)
synthesis
78
4.2.3 Microwave assisted synthesis of Guar esters via
cyclic anhydride
79
4.2.4 Optimization of Reaction Conditions
85
xvi
SECTION III
4.3 Esterification of Cellulose with Fatty acids via acid
chloride Route
91
4.3.1 Fatty acid chloride synthesis and characterization
by elemental analysis
97
4.3.2 Mechanism of Ester formation 99
4.3.3 FTIR Spectra Analysis 100
4.3.4 1H-NMR characterization of 136-145 102
4.4 Determination of degree of substitution of Guar Gum derivatives
103
SECTION IV
4.5 Testing of Guar Gum Derivative 104
4.4.1 Surface Morphological studies of guar gum derivatives
104
4.4.2 Solubilities Determination of Modified Compounds
107
4.4.3 Determination of Water Holding Capacity and gelation properties of guar gum derivatives
109
Conclusion 115
References 118
Annexure 1: List of Publications 136
Annexure II: Fellowship Report 137
xvii
LIST OF FIGURES
Figure No Title Page No
1.1 Types of natural gums 3
1.2 guar gum export worldwide 4
1.3 Structure of Guar Gum 5
1.4 Sequence of Galactose and Mannose in Guar
Gum
6
1.5 Application of guar gum 8
4.1 comparison of antioxidant potential of
phenolicacids and their esters
71
4.2 SEM photomicrographs of native guar gum 102
4.3 SEM micrographs of Native Guar and Guar
Esters (120-124)
103
4.4 SEM images of Microwave induced derivatives 104
4.5 Agglomerate morphology of Compound
145&146
105
4.6 Comparison of water holding capacity of guar
Gum derivatives synthesised by different routes
109
xviii
LIST OF TABLES
Table No Title Page No
2.1 Commercially available Cationizing Agents 14
3.1 Types of solvents used for determination of
Solubilities of guar derivatives
60
4.1 Types of Phenolic Acid used for esterification 63
4.2 Radical Scavengeing activity of compounds 120-124 72
4.3 Microwave assisted esterification of guar via aliphatic
anhydride
79
4.4 Microwave assisted esterification of guar via cyclic
anhydride
82
4.5 Effect of concentration of iodine on DS value 85
4.6 Linear relationship between time interval of
Microwave heating & DS values 87
4.7 Effect of Acid anhydride concentration on Degree of
Substitution 88
4.8 Types of Fatty acid chlorides used for fabrication of
Novel derivatives (136-145)
90
4.9 Conditions and Results of guar esterification
mediated by Acid chloride-pyridine Route
95
4.10 Elemental analysis of fatty acid chlorides synthesis
via thionyl chloride 96
4.11 Characteristic IR Absorptions of guar esters 137-145 99
xix
4.12
Solubility Data of guar Derivatives
106
4.13 Swelling Index of modified guar gum samples 108
4.14 Gelation properties of modified guar gum samples
111
xx
LIST OF SCHEMES
Scheme No
Title
Page No
2.1 Reaction Mechanism for catanization of polymer backbone 15
2.2 The quaternization of GG using CHPTAC as etherifying 16
2.3 Reaction Scheme for acrylation of Guar gum 18
2.4 Synthetic Route for GG-g-MA photopolymerize macromonomers 19
2.5 Synthetic Route for Polyoxyalkylamine Guar Derivatives 21
2.6 Synthesis of guar gum-g-epichlorohydrin derivative 22
2.7 Methylation of guar gum by microwave heating/conventional
Method
23
2.8 Synthesis of carboxymethyl guar (CMG) 24
2.9 Sulfation of Guar gum by chlorosulfonic acid 26
2.10 Synthesis of palmitoylated guar via palmitoyl chloride 28
2.11 Esterification of Galactomannan via Anhydride 29
4.1 Scheme 4.1 Esterification of GG-1 via insitu activation of
Phenolic acid
64
4.2 Reaction Mechanism for esterification of guar gum by insitu
activation of Phenolic acid with DCC, DMAP coupling Reactions
65
4.3 Reaction mechanism of DPPH 71
4.4 Iodine Catalyzed esterification of GG-2 via Acetic, Propionic and
butyric anhydride
75
4.5 N, N-dimethylaminopyridine Catalyzed esterification of GG-2 via
Phthalic anhydride
76
4.6 Microwave assisted guar esters synthesis via cyclic anhydride 8
4.7 Proposed Mechanism for synthesis of fatty acid chloride 92
4.8 Schematic Plot of the conversion of guar gum with fatty acids
Via Acid chloride-pyridine route
94
4.9 General reaction mechanism of the esterification of guar gum 97
1
Guar gum
INTRODUCTION
2
1. INTRODUCTION
1.1. Preamble
“GUMS” has wide range of applications since the beginning of civilization.
According to the Bible “They presented unto him (Jesus) gifts; gold, frankincense
and myrrh (natural gums)”.The ancient Egyptians used myrrh and netron gums for
embalming of mummies.[1] For thousands of years, whole world have relied on
the natural gums as a source of food and medication. Natural gums are high
molecular weight resinous polysaccharides and their derivatives principally grow
in Asia and Africa [2]. Chemically, gums are complex polysaccharides consisting
of variety of salts and sugars more common are D-mannose, D-galactose, L-
arabinose, and L-rhamnose etc along with different ions such as calcium, sodium,
potassium [3]. There is wide diversity in chemical composition, branching
pattern, type of chemical linkage of these gums, so infinite number of chemical
structures are possible. They are classified as seaweed gums, seed gums, and
microbial gums (Figure: 1.1).
The rheological properties of these natural hydrocolloids are responsible for their
multidimensional applications in various industries such as cosmetic, food, textile,
pharmaceutical, oil &drilling etc [4]. Now a days there is increasing trend of
modification of these natural biopolymers by different physical and chemical
methods which improve their quality and properties. These modified biopolymers
have replaced many of the older, established petroleum based synthetic polymers
[5]. The development and commercialization of improved modified gums has
given severe competition to synthetic polymers in recent years .As a result new
class of organic polymers has been produced, which have properties and
applications superior to and similar to synthetic polymers. [6-8].
3
Figure: 1.1. Types of natural gums
1.2. Guar Gum
Guar gum is one of outstanding representative of this new generation of plant
gums. It is cold water soluble, non-ionic polysaccharide extracted from the seeds
Of Cyamopsis tetragonolobus (leguminous family) [9]. It is cultured in semiarid
and subtropical areas of Pakistan and India and to some extent to North Africa and
South America (Figure.1.2.). Guar was introduced into the United States from
India in 1903 [10]. Extraction technology of guar gum was commercialized in
USA in 1953 by General Mills inc and Stein, Hall & co. its introduced as a
substitute of loctus bean gum during world war (1940) due to shortage of loctus
bean gum for paper industry [11] but now a days it becomes top ranking industrial
gums due to its fascinating properties.
4
Guar gum has known as “Black Gold” because demand supply has turned it into
cash crop and precious commodity [12-14]. The world consumption of guar gum
reached at 150,000 tons per annum which got a further boost by introduction of
different modified forms. About 95 percent of the global market of guar products
is covered by India and Pakistan. Guar gum variety produced in Indo-Pakistan
subcontinent cannot be matched because of favourable climate conditions than
rest of world [15]. US consumption of guar seed and derivatives is estimated to be
40,000 tons per annum. Increasing demand originating from oil and drilling
industries of USA and Middle East.USA is the major exporter of guar and its
derivatives [16].
Figure 1.2. Exporter of Guar gum World wide
India, 80%
Pakistan, 15%
Rest World, 5%
5
1.2.1 Chemical Structure, Properties of Guar gum
Guar gum, a natural hydrophilic hydrocolloid belongs to the galactomannan family of
polysaccharides consisting of mannose backbone and galactose side branching [17]
.Chemically it consist of D-Mannopyranosyl backbone (β-1 4 glycosidic linkage)
along with D –glucopyranosyl side branching (α-1 6 glycosidic linkage). (See
Figure 1.3)
Figure: 1.3. Structure of Guar Gum
6
The mannose to galactose ratio ranges from 1.6:1 to 2:1 owing to the variation in
geographical origin [18]. Initially, it believes that galactose side groups are more
uniformly distributed at regular intervals along the mannose backbone. But more
recent investigations show random distribution of side branching [19]. But there is
still debate about exact nature of this interaction (Figure 1.4.). GG is one of the
highest molecular weight naturally occurring polysaccharides .Its molecular weight
ranging from1-2 MDa [20]. GG has the aptitude to produce highly viscous, aqueous
solution showing pseudoplasticity even at low concentrations due to high molecular
weight (up to 2 MDa), due to the presence of extended repeating units of sugars
linked by hydrogen bonding [21-23]. This characteristic is also responsible for its
solubility and complex formation. Due to its unique rheology modifying properties, it
is being widely used across a comprehensive range of industries spectrum like
cement, cosmetic, food ,oil well drilling, paper, paint, pharmaceutical and textile etc
[24-31]. Functional properties of gums depends upon their chemical structure,
mannose to galactose ratio, molecular weight and nature of branching and some other
properties so guar is more water soluble then Loctus gum due to more galactose side
groups [32], so it is established as better emulsifier, water builder, stabilizer and
thickener. Its water thickening potential is 5-8 times higher than starch [33].
A
Even Distribution of Galactose
B
Random Distribution of Galactose
Mannose Backbone
Galactose side chain
Figure: 1.4. Sequence of Galactose and Mannose in Guar Gum
7
Non-ionic nature and stability over wide pH range (5-7) of guar solution is
responsible for constant viscosity and compatibility with different salts and other
gums. It is available in different forms from seed to powder depending upon its
applications. Commonly it is white to yellowish colour free flowing powder with
variable viscosities which is insoluble in all organic solvents but soluble in hot and
cold water [34]. It acts as rheological modifier in many water based systems due to
high viscosity even at low concentration (4000+cps, 1% soln at 25°C), which is
superior to all available naturally occurring gums [35]. Strong alkalies and acids tend
to decrease its viscosity and hydrolysis of polymer units.
Chemical composition of guar seed varies from seed to seed due to different
geographical origins but mainly it consist of 0.8% ash,10-12% moisture, 1-1.5% fat,
4-5% protein,1.5-2.5% fiber and rest is carbohydrate galactomannan [36]. Guar gum
solution exhibited NonNewton behaviour, thixotropic above 1% concentration;
pseudoplastic, sheer thinning effects [37].
1.2.2 Applications of guar gum
The exceptional rheological properties of GG, proved its consumption in industries
viz cement, cosmetic, explosive, food, hydraulic fracturing fluids, oil drilling, textile,
paper, paint, , pharmaceutical, etc. It is always an important agro commodity,
fascinating wide interest of academic and commercial researchers all over the world
[38-40].
Physiological and therapeutic effects associated with Guar gum makes its ideal
candidate for using as binder and disintegrator in pharmaceutical industries. The
therapeutic effect of guar gum is due to its ability to swell swiftly in water to form
viscous gels. When inhaled, guar gum gets adsorbed in the stomach and halts or alters
absorption of glucose, cholesterol and possibly drugs. Some of its modified products
are used as binders and disintegrators in tablets to give consistency to drug powder
[41]. Today guar gum is also used as thickener, stabilizer in pharmaceutical
formulations and a controlled-release agent for drugs due to its high hydration rate
(Swelling in aqueous media).When mixed with different ingredients in formulation of
tablets it forms a protective layer and consequently, drug comes out from the tablet
8
made in guar gum base in a constant mode accomplishing the anticipated kinetics
effect [42]. It also masks its unpleasant taste and odour of drug and improves its
stability and drug releasing properties. The role of guar gum and its derivatives to
control blood sugar is well known in diabetes which resulted due to insufficiency of
pancreases to produce enough insulin, or when the insulin cannot effectively utilized
by body . This leads hyperglycemia [43]. By absorbing excess postprandial plasma
glucose, insulin and triglycerides plant gums showed exceptional
hypocholesterolaemic effect [44].
Figure: 1.5. Applications of Guar Gum
Applications
Cosmetic industry
Pharmaceutical industry
Paper industry
Food industry
Paint Industry
Oil drilling industry
Textile
industry
9
Major market of guar gum and its derivatives is in petroleum industry. Recently prices
of guar have become historical high due to increased consumption by oil drilling
industry of USA and Middle East, where it is used as stabilizer and gelling agent in
hydraulic fracturing fluids [45-46]. Guar gum and its derivatives like hydroxypropyl
guar gum (HPG) and carboxymethyl gum (CMG) have found a broad range of
applications in petroleum industry as an additive for water and water /methanol based
cracking liquid.
Cationic guar has major application in paper industry. Depolymerized, Carboxymethyl
guar (CMG), cross linked guar is broadly utilized in textile printing [47]. These
modified gums derivatives give intense colour yield, compact bleeding effect, sharpness
and effective penetration of dye. The cationic guar derivative of GG is used to thicken
various cosmetic products. These guar products are specially used to impart
performance functions such as conditioning, foam stability, softening and lubricity in
cosmetics and toiletries like hair and skin care products, cleansing and bathing products
[48]
Water proofing, thickening and foam stabilizing properties are required in the
preparation of explosives. Oxidized guar gums are the most commonly used
polysaccharides to thicken slurry explosives. In the production of water-resisting
ammonium nitrate stick explosive, guar gum is used as a binding agent [49]
In food industry guar is applied as emulsifier, stabilizer, thickener, preservative agent
and viscofier. Major use of guar and its derivative is in food industry because it is non-
toxic, economical, abundant hydrocolloid. It improves texture and gives uniform
viscosity to food products. In frozen food items it reduces crystal growth and act as a
stabilizer [50-51].
Demand of guar gum is escalated day by day due to increased applications in food and
petroleum industry .so there is need to modified guar gum to minimize drawback
associated with native gum. Many different derivatives or modified form are
commercially available. These are discussed briefly in proceeding sections [52].
10
1.3 Aims and Objectives
Overall aims and objective of this research project was to explore novel routes
for synthesis and characterization of native guar gum to enhance its functionality and
properties in multidiscipline sectors. This work has been done by modification of
already developed method and development of novel routes for synthesis. Special
focus of this research project was
To adopt the economically favourable synthetic routes with maximum degree
of substitution.
Avoid extreme or unsafe reagents and reactions dangerous to environment.
To prepare Green and economical biopolymers.
To find out novel, Innovative and elegant methods for synthesis.
Section I
Major interest was to prepare new guar esters via in situ activation of the cinnamic
acid and its analogues by DCC/DMAP coupling reactions .These newly developed
derivatives were evaluated for their antioxidant potential by DPPH radical scavenging
activity method. Reaction conditions were optimized for each experiment to get esters
with maximum degree of substitution (DS), which was measured quantitatively by
Wurzburg method. Interest was to graft and analysed antioxidant moieties to guar
backbone which can enhance its uses in pharmaceutical and food industry. For
Analysis several techniques were used such as 1H-NMR, FTIR and SEM for surface
morphological studies.
Section II
Second goal was to develop and optimized green, cost effective and environmentally
friendly microwave assisted modification of GG via acid anhydride to save time and
energy. The major interest was to study the factors that influence the reaction rate and
DS values of modified Guar. Effects of different variables such as molar ratio of
11
regents, catalyst amount and reaction time on the DS of the esters were examined.
Physical properties such as solubility and rheology of modified polymers were also
studied. Total amount of anhydride consumed was calculated by titration method.
Different instrumental techniques were used to elucidate the structure and properties
of derivatives like H-NMR, FTIR and SEM.
Section III
First time Guar esters of long chain aliphatic carboxylic acids (fatty acid) were
prepared and examined. Esterification was done in two steps, first goal was to prepare
acid chloride by refluxing acid with slight excess of thionyl chloride, and product was
confirmed by elemental analysis. Ten different types of acid (C5-C18) were used for
derivatization. Reaction Mechanism for synthesis of fatty acid ester of guar was
studied in detail. Physical properties of the esters were examined as well. DS was
calculated by titration method and structure elucidation was done by FTIR, H-NMR
and SEM techniques.
12
Guar gum
Literature Review
13
2. LITERATURE SURVEY
Derivatization of guar gum (GG) was developed in 1960s as an alternative thickener
to plain guar gum by General Mills Inc by commercializing hydroxypropyl guar
for hydraulic fracturing. Guar gum possessed exceptional swelling ability and
hydration capacity but have concerns about solution clarity, organo-solvents solubility,
unrestrained rate of hydration, decrease in viscosity on prolong stay, microbial
contamination susceptibility etc. Modification of Guar leads to noticeable changes in
properties, such as, decreased hydrogen bonding, profound solubility increase in various
organic solvent systems, enhanced electrolyte affinity, increased solution clarity and
stable viscosity [53-54]. Guar molecule has maximum of three free hydroxyl groups per
anhydro sugar units. So substitution degree might be three at its maxima and can be
surpass to three, if additional hydroxyl groups are available for subsitution [55].
Average number of OH- groups per sugar unit is known as degree of substitution or DS
value. Primary hydroxyl group at C6 position is more susceptible to change but C2 and
C3 positions are also good reacting sites (See figure1.3.)[56]
Alteration of GG is done by two ways either chemical modification or physical
modification to form different derivatives with variable degree of substitution [57-58].
These chemical modifications involve replacement of free hydroxyl group of guar
backbone by different cationic, anionic, amphoteric and non-ionic groups. Physical
modification means enzymatic, acidic and basic hydrolysis of GG-1 to yield low
molecular weight gum. Modification enhances properties and application of guar in
broad spectrum of industries. Several techniques may be applied to obtain different
derivatives of guar gum with variable DS values. [59]
2.1. Cationic guar gum
Cationic guar with quaternary ammonium functional group has been used in personal
care products as substantive conditioning agent. Reagents used for cationization are
mostly quaternary ammonium salts with reactive side groups [60]. They are available in
the stable chlorohydrins or reactive epoxide form.
14
Table 2.1 Commercially available Cationizing Agents
Commercial Name
CHPTAC
3-chloro-2-hydroxypropyltrimethyl ammonium chloride
CHPDLAC
3-chloro-2-hydroxypropyldimethyl Dodecyl ammonium chloride
CHPCDAC CHPDSAC ETA
3-chloro-2-hydroxypropylcocoalkyldimethyl ammonium chloride 3-chloro-2-hydroxypropyldimethyl Stearyl ammonium chloride 2,3-epoxypropyltrimethyl ammonium chloride
15
Cationic groups are covalently bounded to guar backbone and enhance the gum
affinity to anionic surfaces like skin and hair. Cationic guar is more widely used
polymer in cosmetic industry as compare to other cationic biopolymers such as starch
and cellulose due to its excellent lubricating and conditioning effects. Commercially
cationic derivatives of guar are available with DS lower than 0.1 [61].
Oberstar et al. [62] formulated conditioning shampoo containing cationic derivatives
of guar to improve lustre and texture of hairs.
Cationic guar samples of variable molar mass and charge density were prepared by
levy et al. [63] by reacting cationic reagent 2, 3-epoxypropyltrimethylammonium
chloride to guar molecules in two steps. First step involved synthesis of cationizing
reagent and second step involved grafting of cationic group on guar backbone as
shown by reaction scheme 2.1.
Scheme: 2.1. Reaction Mechanism for catanization of polymer backbone
Dasgupta [64] succeed to prepare cationic derivatives of GG with DS upto 0.1 then
higher DS up to 1 have been achieved by Cottrell et al. [65] in isopropyl
alcohol/water media Or Pal et al. prepared same derivatives in water media for
potential use in personal care and food industry.
16
The quaternization of guar gum by means of CHPTAC (etherifying agent) under the
acceleration of NaOH was studied by Y.Huang et al. [66] they investigated the
thermal and mechanical stability of hydrogel formulated by copolymerization of
cationic guar (CGG) with poly (acrylic acid) (PAA). They succeed to attain DS of
0.35 determined by titration method. (See Reaction scheme 2.2.)
Scheme: 2.2. The quaternization of GG using CHPTAC as etherifying
Extensive study was done by Bigand et al. [67] on cationization of xylan or
galactomannan (guar) by using 2, 3-epoxypropyl trimethylammonium chloride (ETA)
act as acylating agent under the influence of basic conditions. Reaction conditions
were optimized to obtain derivatives with maximum DS value. They succeed to
obtain substitution degree of 1.3 and maximum grafting rate of 48%.Derivatives were
confirmed by 1H-NMR, 13C-NMR, FTIR spectroscopic techniques and elemental
analysis. Reaction Mechanism is same as shown in Scheme 2.1.
2.2. Grafted Guar Gum
Graft co-polymerization of various monomers onto the backbone of GG and other
biopolymers is a field of interest for polysaccharide researchers in last decade.
Grafting is done by generating free radicals by chemical initiation on polymer [68].
Grafting impart important properties to modified polymers which are superior to
native one. Grafting is done by thermal, chemical, photochemical methods. Chemical
method is easier and widely studied method which involves easily available and
economical reagents and equipments and easily adapted in lab scale. To date, a large
17
volume of work has been done on grafting of vinyl monomers like acrylamide,
acrylonitrile, methylmetacrylate etc on guar gum backbone using redox initiating
systems. These grafted polymers have wide applications in textile printing, paper
industry and works as flocculants in oil and drilling industry.
Successful microwave mediated modification of guar –g-polyacrylamide; a
copolymer was done by V. Singh & co-workers [69] without any catalyst. Reaction
results indicated greater grafting ratio of 66.66% as compared to 49.12% grafting
obtained by conventional method. Different spectroscopic methodologies were used to
confirm the formation of copolymer such as FT-IR, 1H- NMR, thermal and
mechanical stability was checked by XRD and TGA.
O-Carboxymethyl-O-hydroxypropyl guar gum (CMHPG) is a hydrophilic hydrogel
commercially available with different DS value to prepare controlled colon drug
delivery systems. To enhance its thermal characteristics H. Y. Shi et al. [70] grafted
Poly (N-isopropylacrylamide) (PNIPAAm) side chain on polymer. Solubility. Phase
transfer behaviour, grafting ration of these new polymer graft copolymer was
characterized in aqueous media.
J. Biswal et al [71] discovered novel route for grafting of acrylamide on GG using
high energy gamma radiations. Comparison of microwave assisted and radiation
induced grafting was studied. Results conclude that gamma radiation grafting is better
route for polymer modification as compared to microwave assisted copolymerization
with greater grafting ratio. FTIR, XRD, TGA, SEM results indicated more thermal
stability of new grafted co-polymer as compared to native gum.
Comparison between conventional redox grafting and microwave assisted grafting of
acrylamide on carboxymethylated guar was done by Sagar Pal et al. [72] Novel
derivatives CMG-g-PAM synthesis by microwave assisted grafting method showed
better flocculation characteristics as compared to other synthesis by conventional
redox grafting.
Shenoy and D. Melo [73] fabricated and studied the acrylated guar gum and its effect
in acrylic emulsions as compared to native gum. Rheological behaviour, film forming
18
ability, clarity, thermal and mechanical strength of these new derivatives was studied
in detail. Acrylation of GG done in two steps, step one involved synthesis of acrylated
reagent and second step involved formation of acrylated gum (Scheme 2.3.). Result
concluded that emulsion with acrylated gum has greater tensile strength, lower
viscosity, increased elongation and better clarity. Maximum DS value obtained was
0.56 for acrylated guar.
Scheme: 2.3. Reaction Scheme for acrylation of Guar gum
Novel derivatives of guar gum grafted poly (acrylamide-co-diallyldimethylammonium
chloride) was discovered by Mclean et al [74] and studied its behaviour as
hydrophobic wood resin adsorbent in paper making. Result showed that GG-g-p (AM-
co-DADMAC) act as better polymer fixative as compared to other commercially
available fixatives.
Wang et al. [75] explore the potential use of guar-grafted (poly-sodium
acrylate)/Medicinal stones as PH responsive superabsorbent hydrogels.
Characterization of these hydrogels was done by FTIR, XRD, TGA, DTA etc
techniques.
19
Another monomer which is widely grafted on guar backbone is Methyl Methacrylate.
Chowdhury et al. [76] copolymerized guar and MMA using ceric ammonium
sulphate/dextrose as redox initiators. Modified polymer was analysed by FTIR and
TGA techniques.
Important discovery was done by Tiwari et al [77] by preparing methacrylated guar
used for tissue engineering scaffold fabrication. Modification was done by reacting
hydroxyl group of guar with glycidyl methyl methacrylate (GMA). As a result
hydrophilic photopolymerizable guar –methacrylate was formulated and characterized
by NMR techniques (scheme 2.4).
Scheme: 2.4. Synthetic Route for GG-g-MA photopolymerize macromonomers
Singh et al. [78] explored the application of GG-g-MA graft copolymer for removal of
health hazard Cr (VI) from aqueous system or industrial waste. They had done
copolymerization by using persulfate/ascorbic acid as a redox pair. Same copolymer
was synthesis by A.Tivari et al [79] for tissue engineering scaffolds in situ production.
20
Cerium (IV) incited grafting of polyacrylonitrile on to guar gum was investigated by
Thimma et al. [80] Reaction conditions were optimized for each experiment. Effect of
temperature, initiator concentration, and guar and acrylonitrile molar ration was
investigated on grafting percentage. Hydrolysis of modified GG was done to obtain
anionic guar with good water absorbency capacity.
Trivedi et al. [81] established a reaction mechanism for grafting of acrylonitrile on
partallycarboxymethy guar gum (DS-0.49) to obtained novel derivatives using cerric
ammonium sulphate as a catalyst. Reaction conditions were varied such as strength
of HNO3 (NH4)2Ce (NO3)6, variation in monomer concentration and time intervals
to obtain copolymer with highest percentage of grafting. For the analysis of graft
polymer FTIR, TGA, DSC has been applied. Surface changes were observed by
scanning electron microscopic (SEM) technique.
An attempt was made by Behari et al [82] to crosslinked environmental friendly
monomer N-vinyl formamide on GG by using bromated -ascorbic acid accelerating
system.GG-g-NVF novel grafted copolymer was characterized by IR-spectroscopy
and different thermal techniques such as XRD and TGA/DSC.
Gliko-Kabir et al. [83] had done Crosslinking of guar by glutaraldehyde (GA).
Physiochemical changes or grafting efficiency of modified of gum were characterized
by different thermal spectroscopic techniques such as differential scanning
calorimetry TGA/DSC along with XRD techniques.
Cunha et al. [84] copolymerized GG with glutaraldehyde to obtain a high molecular
weight novel hydrogel which has potential candidate for biomaterials. Rheological
behaviour of these gels was studied along with characterized by GPC, XRD, SEM and
TGA techniques.
New hydrophobic derivatives of guar were prepared by Ahmad Bahamdan [85] by
reacting hydroxyl functional group of GG with series of polyalkoxyalkyleneamide.
Reaction sequence included carboxymethylation, methylation and amidation of guar
as shown by scheme 2.5. Grafting ratio was confirmed by FTIR and NMR techniques.
21
Application of these hydrogels in hydraulic fracturing fluid composition was also
studied by Ahmad Bahamdan and William H. Daly [86].
Cross linking of polyethylene glycol diglycidylether (PEGDGE) to guar polymer was
done by G. Leone and R. Barbucci [87] to create a new hydrogel to use in biomedical
field. These hydrogel was examined by FTIR, AFM and SEM analysis.
Scheme: 2.5. Synthetic Route for Polyoxyalkylamine Guar Derivatives
To impart hydrophobic characteristics and to improve biocompatibility of carbon
nanotubes (CNTs) Li Yan et al. [88] covalently grafted guar gum (GG) on the surfaces
of multiwall carbon nanotube (MWCNT). As a result GG–MWCNT complex was
formed. To fabricated magnetic copolymer they reacted GG-MWCNT with iron
nanopartices resulting new polymer GG–MWCNT–Fe3O4. Resultant nanocomposites
were analyzed by FTIR, TGA/DTA, TEM, XRD and UV–Vis spectroscopy.
Guar gum-g-epichlorohydrin was investigated by T. Hongbo et al. [89] by reacting
epichlohydrin with guar gum in the alkaline condition as shown below in scheme 2.6.
22
Scheme: 2.6. Synthesis of guar gum-g-epichlorohydrin derivative
2.3 Guar gum ethers
Etherification of polysaccharides is an important mechanism to produce many
commercially important derivatives with peculiar properties. Mostly ethers are
synthesis via Williamson ether synthesis mechanism. In which free hydroxyl group of
guar alkylated in the presence of strong alkali and form alkoxide ions. These ions
react with etherifying agents to form guar ether by SN2 mechanism.
2.3.1 Methylated guar
Methylation of guar gum is an important tool to know about the structure composition
and constitution of polymer. Denham and Woodhouse and Haworth method is
consider as standard method for methylation of polysaccharides by using DMS in
alkaline condition. Methylation is done by nucleophilic substitution mechanism.
V. Singh et al. [90] Fully methylated GG by using domestic Microwave oven within
4min. They used dimethy sulphate as methylating agent and sodium hydroxide as
catalyst. Product forms were analyzed by IR spectroscopy. (scheme2.7.A)
D. Risica et al. [91] done etherification of Guar by using Dimethyl Sulfide (DMS) and
methyl iodide (MI) with excess of sodium hydroxide (NaOH). (Scheme 2.7.B)
23
Scheme: 2.7. Methylation of guar gum by microwave
heating/conventional Method
Viscosity measurement, FTIR and H-NMR give important information about DS
value of methylated guar.
2.3.2 Carboxymethylated guar
Carboxymethylation is most widely studied conversion of naturally occurring
biopolymers to produce commercially important biopolymers with promising
properties. Carboxymethylated derivatives of guar gum are extensively applied in
paper and oil industry. Mostly monochloro acetate is used to impart carboxymethyl
functional group on guar backbone.
B. R. Sharma et al. [92] studied carboxymethylation of guar by using acrylamide and
sodium hydroxide.variable was studied for each experiment and modified gum was
analysed by FTIR.
Non aqueous method for carboxymethylation of guar gum was discovered by K.S.
Parvathy et al. [93] Carboxymethylation was done by using monochloroacetic acid
and catalytic amount of NaHCO3 in dry state. Modified guar (CMG) was synthesised
with variable DS values ranging from 0.065 to 0.675 at variable reaction parameters.
The progress of the reaction was monitored by FTIR and 13C- NMR spectral data.
(See scheme 2.8.)
24
Scheme: 2.8Synthesis of carboxymethyl guar (CMG)
Partially carboxymethylated guar was synthesised by Sagar pal [94] by using sodium
monochloroacetic acid in presence of sodium hydroxide. The resulting products were
characterized by intrinsic viscosity measurement, molecular weight determination,
elemental analysis, and TGA/DTA, 13C-NMR and FTIR techniques.
Mazhar pasha and Swamy N. G. N [95] done chemical derivatization of guar gum
molecule to Sodiumcarboxymethyl hydroxypropyl guar upto DS 1.5.Effect of PH ,
electrolytes, viscosity measurements and spectral analysis indicated higher thermal
stability ,controlled rate of hydration as compared to native gum.
Application of carboxymethyl guar gum for colon target drugs was studied by V.
Kumar et al. and A. Sullad et al [96-97] in two different studies. G. Dodi et al. [98]
also done chemical modification of guar by derivatization of carboxymethyl group for
biomedical applications especially for oral drug delivery of hydrophilic
macromolecules. The resulting products were analyzed by different spectroscopic and
thermal techniques.
25
2.3.3 Sulfated guar gum
Sulfation of polysaccharides imparts diverse biological activities to polymer backbone
which have wide spectrum of applications in various industries like explosive
industry, pharmaceutical industry, paper and pulp industry.
Important discovery was done by N. M. Mestechkina et al. [99] by sulfating different
galactomannan including guar by SO3-pyridine as sulfonating agent and
Dimethylformamide as solvent. They concluded that reaction temperature was
important factor in determination of degree of substitution. They succeed to obtain DS
1.4-1.8.
Another attempt was made by A.M. Gamal-Eldeen et al. [100] to analysed cancer
chemopreventive, antioxidant and anti-inflammatory properties of sulphated guar gum
(SGG). They used SO3-formamide complex as sulfonating reagent and concluded that
SGG was an alternative of native guar in food industry to minimize risk of cancer.
Xiowang et al [101] evaluated antioxidant potential of sulphated guar gum. They
prepared sulphated gum of different DS value 1.92-2.85 and molecular weight.
Product formed was characterized by FTIR and 13C-NMR. Molecular weight
distribution was done by size exclusion chromatography (scheme 2.9.).
Scheme: 2.9.Sulation of Guar gum by chlorosulfonic acid
26
A. V. Singh et al. [102] formulated sulfated guar gum, ion exchange resin used for
elimination of poisonous metals from steel industry waste. Same work was done by
Singh et al. [102]. They Synthesis guar-sulphonic acid cation-exchanger and explored
its application as metal ion removal from mine water waste.
J. Wang et al. [103] reported that sulphated guar gum showed significant biological
activities. They prepared sulphated guar gum derivatives by Box–Behnken statistical
design. Presence of sulphated groups was confirmed by FT-IR, X-ray spectroscopy,
size exclusion chromatography (SEC) along with laser light scattering (SEC–LLS)
analysis.
2.3.4 Hydroxyalkylated guar gum
Hydroxypropyl guar (HPG) was first commercially prepared guar ether in 1960 by
General Mills Inc USA. Hydroxypropyl guar (HPG) is mostly used in oil
drilling industry. It has numerous applications in paper/textile industry as
sizing agent and pigment printing thickener.
Boonstra et al. [104] prepared non lumping hydroxyalkylated guar derivative with
DS value of 0.12 to use as a thickener in textile printing.
O-(2-hydroxyethyl), O-(2-hydroxypropyl), O-(2-carboxymethyl) guar gum derivative
was prepared by H .Prabhanjan et al [105] with variable reaction parameters. Rate of
hydration, rheological behaviour, viscosity, moisture contents of resultant products
were analyzed.
Rheological behaviour of hydroxyethyl guar (HEG) and hydroxypropyl guar (HPG)
and its derivatives were studied in detail by R. Lapasin et al. [106] under continuous
and oscillatory shear flow rate. They conclude that molecular weight and amount of
polymer have visible effect on rheology of gum along with temperature.
27
Xiong et al. [107] developed novel route for synthesis of hydroxypropyl guar by
phase transfer catalysis. Typical procedure involved the reaction between guar,
propylene oxide and HTAC (hexadecyl trimethyl ammonium chloride) as phase
transfer catalyst. Result showed modified guar showed higher viscosity, stability and
light transparency as compared to native one.
G.Wang et al. [108] developed biocompatible sol-gel silica matrix for the
encapsulation of drugs by incorporating a new hydrophilic silica precursor, tetrakis (2
hydroxyethyl) orthosilicates (THEOS) and result proved that THEOS transit from
solution to gel quickly in aqueous media devoid of any additional organic solvent and
catalyst.
Determination of degree of substitution of Hydroxypropyl guar gum (HPGG) was
studied by Yannan Chen et al. [109] by pyrolysis of gum at C6 position. Gas
chromatography and GC-MS spectrometry were used for investigated DS of resultant
products.
A new chemical method was introduced by Wua et al. [110] to determine substitution
pattern of hydroxypropyl guar. A novel method involved periodates oxidation of gum.
Product formed was investigated by IR and NMR techniques.
A novel derivative of guar gum hydroxyethyl amino hydroxypropyl guar gum
(EAHPG) was prepared by Y. Zhao et al. [111] by chemical alteration of p-
toluenesulfonate activated hydroxypropyl guar gum with ethanolamine through
nucleophilic substitution reaction. Results were confirmed by FTIR and NMR
spectroscopy.
28
2.4 Guar gum esters
Different synthetic routes are commercialized in recent years to obtain
polysaccharides esters with variable properties and applications. Guar gum act as
potential emulsifier and thickener in food industry because they are non-toxic,
biodegradable and having good emulsifying and antioxigenic properties, to increase
the emulsifying property of guar B. Tian & C. Dong [112] prepared palmitoylated
guar gum derivatives under heterogeneous reaction conditions. Reaction procedure
involved reaction between guar hydroxyl groups and palmitoyl chloride (Scheme
2.10) in toluene and pyridine as initiator. Modified gum was characterized by FTIR,
XRD and TGA/DTA techniques. Degree of substitution was determined by
saponification method.
Scheme: 2.10 Synthesis of palmitoylated guar via palmitoyl chloride
Prashanth et al [113] developed ecofriendly, green method for preparation of three
different types of galactomannan esters by reacting polymer with acetic, succinic and
octenylsuccinic anhydride under anhydrous condition with mild catalyst
NaHCO3.Main focus was to avoid strong alkali and far excess of water thus making
whole process cost effective.(Scheme 2.11)
29
Scheme: 2.11 Esterification of Galactomannan via Anhydride
An important discovery was made by Rumiko Fujioka et al. [114] to increase
biodegradability of native guar by esterification of succinate group on polymer chain.
They prepared novel superabsorbent hydrogels in DMSO by reacting guar with
succinic anhydride and 4-dimethylaminopyridine as a catalyst. Resultant hydrogels
exhibited excellent water absorbency and biodegradability to make them ideal
candidate for biomedical applications.
M. A. Shenoy et al. [115] acetylated the HPG (hydroxypropyl guar) to use as filler in
unsaturated polyester composites. Derivatized guar increased filler-polymer
interaction by increasing hydrophobic nature of polymer.
30
Introduction of hydrophobicity in hydroloyzed guar gum (GGH) and gum Arabica
was done by S. Sarkar, R. S. Singhal [116] by reacting gums oleic acid and n-octenyl
succinic anhydride (OSA). The reaction conditions were optimized for maximum
degree of substitution (DS) which was 0.061, 0.072 respectively for guar oleate, guar
n-octenyl succinate .Resultant esters were analyzed as wall materials in
microencapsulation.
Novel blends from quaternized polysulfone (QPSF) along with benzoylated guar
(BGG) called as QB, and chloromethylated polysulfone (ClPSF) and benzoylated
guar (BGG) known as ClB was introduced by Yihong Huang et al. [117] by reacted
benzoyl guar and quaterinized polysulfone . Differents techniques were used to
confirm the formation of these hydrogels such as FTIR, SEM, AFM and DSC and
tensile tests revealed typical phase separation between blends.
31
Experimental
32
3. EXPERIMENTAL
3.1 Materials
All commercially available compounds need no purification except where stated. The
nitrogen atmosphere is created through standard syringe techniques which were
employed for moisture or air sensitive reactions. Flame dried glass apparatus was
used to avoid moisture. A formed Grubbs system of aluminium columns was applied
for drying the solvents; manufactured by Anhydrous Engineering. When stated DMF
and DMSO were dried over 4 Å MS beads for 24 h three times and stored under
nitrogen. The reactions were cutinized by precoated Merk-Keiselgel 60 F254
aluminium backed TLC plates. The spots were visualized by UV254 light.
Guar gum (GG-1) pharmaceutical grade was purchased from Pakistan gum industries
Karachi with molecular weight of 1.053×106 g/mol determined by GPC/MALS and
RMS radius is about 55.65 nm. Partially hydrolyzed guar gum (GG-2) with molecular
weight 2.3 × 103g/mol for microwave assisted modification of guar was purchased
from National Colloid Industry (NCI) Karachi. All other commercially available
reagents were purchased by sigma Aldrich, Alfa Aesar, Fluka and Acros organic.
3.2 Measurements
Perkin Elmer Spectrum One FT-IR spectrometer was used to explore infrared spectra
in the solid or liquid state. 1H NMR spectra were recorded exhausting whichever a
Jeol Eclipse 400 MHz or Varian 400-MR 400 MHz spectrometer. 1HNMR spectra of
native gum were done by in situ hydrolysis of guar in DC. Derivatives spectra were
recorded in DMSO-d6 and D2O as a solvent.10mg sample per mL of solvent is used
for analysis. The chemical shifts (δ) are reported in parts per million (ppm), coupling
constants (J) are reported in Hertz (Hz).
High and Partial Vacuum (10-10-4 Pa) Jeol- JSM 5600 LV Scanning electron
microscopy with secondary electron detector at voltage between 1-30kV was used for
surface morphological studies of polymers. UV Spectrophotometer (UV-2800
33
Hitachi) was used for measuring antioxidant assay of compounds 120-124.Vario EL-
III, Germany Elemental analyzer was used for characterization of fatty acid chlorides
135a-135j.
Domestic Microwave Oven Output of 1000 W with ten Microwave power levels
Model No. OM-55-B9 Orient was used for Microwave assisted transformation of
GG-2 via acid anhydrides to fabricated guar derivatives 126-133 via novel routes.
3.3 Methods
3.3.1 Purification of guar gum
GG-1, GG-2 (2.5g) were dissolved in 100 ml of water respectively to obtain (25%)
solution with continuous stirring of 12 h at 58 °C. Saturated Ba (OH)2 solution was
added to precipitate the gum salt [118] by barium complex formation method reported
by many researchers [118]. Separation was done by centrifugation. The precipitate
was acidified (1 M acetic acid) and agitated for 8 h and recentrifuged for 30 min. At
last, the supernatant was separated and washed with 70-95% ethanol, respectively
finally dried at 40 °C overnight.
34
SECTION I
3.4 Guar gum Derivatives with Antioxidant Moieties by insitu
activation of phenolic acid
3.4.1 Synthesis of guar gum cinnamate-GGC (120)
Cinnamic acid 118a (2.66 g, 18 mmol.), dicyclohexylcarbodiimide 119 (3.7 g, 18
mmol.) were added at 0°C to guar gum solution with continuous stirring under
nitrogen. After that 0.4 g DMAP was added. Temperature is raised to 50°C and
reaction performance was monitored by IR (ester peak observed) and TLC
(disappearance of 119) .The temperature of the reaction mixture was brought upto
50°C for 72hr. These Precipitate were splashed with hot ethanol, chloroform and ether
to remove unreacted dicyclohexyl urea. Solvent was evaporated in vacuum to give the
product GGC 120.
DS: (calculated by titration) 0.35
Yield = 66%
FTIR (KBr): cm-1= 3349 (OH stretch), 2920 (C-H stretch), 1670 (C=O ester), 1213(C-
O-C ester)
1HNMR (400 MHz, DMSO-d6): δ ppm = 3.5-5 (sugar Protons), 6.31(1H, d, 8-H),
7.02(1H, d, 7-H), 6.56-6.94(5H, m, Ar-H);
35
3.4.2 Synthesis of guar gum ferulate GGF (121)
In situ activation of Ferulic acid 118b (3.5g, 18mmol) was done by coupling with 119
(3.7g, 18mmol) in the presence of DMAP (0.1 g, 0.5mmol in guar gum solution. The
same protocols were followed, which were adopted for 120. Reaction procedure was
same as above to get GGF -121 as a white powder with good yield.
DS: 0.98 (calculated by titration)
Yield =70.3%
FTIR (KBr): cm-1= 3415 (OH stretch), 2930 (C-H stretch), 1732 (C=O ester), 1238
(C-O-Cester)
1H-NMR (400MHz, DMSO-d6 /D2O): δ ppm = 3.8-5.4 (sugar protons), 3.69 (3H, s,
OCH3), 4.19 (1H, br s, OH), 6.17 (1H, d, 8-H), 6.74 (1H, d, 5-H), 7.02 (2H, m, 2-H
and 6-H), 7.40( 1H, d, 7-H);
36
3.4.3 Synthesis of guar gum Caffeate–GGCa (122)
A solution of guar gum and caffeic acid 118c (3.24g, 18 mmol.) in dry DMF (50mL)
were stirred at room temperature by continuous stirring then addition of 119 (3.7g,
18mmol.) was done and the mixture was stirred at 70°C for 48h under inert
atmosphere. Ester formed was precipitated in ethanol (100ml), precipitate formed was
washed with hot methanol, ether and chloroform respectively to dissolved
dicyclohexyl urea, formed as by-product. Product 122 dried under vaccume with
continuous stirring of reaction mixture.
DS = 0.69(calculated by titration)
Yield: 69.8%
FTIR (KBr): cm-1 = 3335 (OH stretch), 2932 (C-H stretch), 1729 (C=O ester), 1219
(C-O-C ester) 1HNMR (400 MHz, DMSO-d6): δ ppm = 3.2-5 (sugar Protons), 5.35 (2H, br s, 3-OH,
4-OH), 6.91(1H, d, 8-H), 7.60 (1H, d, 7-H), 6.93-7.17(3H, m, 2-H,5-H and 6-H)
37
3.4.4 Synthesis of guar gum Coumarate –GGCo (123)
Coumaric acid 118d (6.608 g, 36 mmol) was dissolved in dry DMSO then (7.6g,
0.037mole) of 119 was added and stirred for an hour. The mixture was added in 3gms
of guar solution in DMSO at room temperature and again stirred for 72 hrs under
nitrogen at 50°C. The precipitates were extracted with ethanol and washed with
chloroform and ether to remove unreacted by products. Product 123 was dried in
vacuo.
DS: 0.039(calculated by titration)
Yield: 50.4%
FTIR (KBr): cm-1 =3335 (OH stretch), 2932 (C-H stretch), 1729 (C=O ester), 1219(C-
O-C ester)
1HNMR (400 MHz, DMSO-d6): δ ppm = 3.2-5 (sugar Protons), 5.35 (1H, br s, 4-OH),
6.13(1H, d, 8-H), 6.65 (2H, d, 3-H and 5-H), 7.32 (2H, d, 2-H and 6-H), 7.41 (1H, d,
7-H)
38
3.4.5 Synthesis of guar gum hydrocinnmate-GGH (124)
Hydrocinnamic acid 118e (1.5 g, 10 mmol) and 119 (2.06 g, 0.01mole) were added in
the reaction mixture (solution of GG-1 in DMSO) at 0°C with continuous stirring.
Agitation of reaction mixture was carried out at 50°C for 24 hrs under nitrogen. When
TLC indicated that all starting material had been consumed the reaction was
quenched. Precipitate formed washed several time with ethanol and chloroform and
dried in vacuo to give the product 124.
DS: 2.34
Yield: 87%
FTIR (KBr): cm-1 = 3366 (OH stretch), 2946 (C-H stretch), 1723(C=O ester), 1250(C-
O-C ester)
1-HNMR (400 MHz DMSO-d6): δ ppm =3.6-5.2 (sugar Protons), 2.53 (2H, t, 7-H2),
2.89 (2H, t, 8-H2), 7.29(5H, m, Ar-H)
39
3.4.6 Determination of Degree of substitution (DS) by
Wurzburg Titration Method
Method [119] of Wurzburg (1964) was tailored to determine the degree of substitution
of guar esters quantitatively. For each trial (0.1g) dry powder sample was weighed
and dispersed in 10ml of 0.5N ethanolic KOH solution and refluxed for 24 h. The
excess soda was back-titrated against 0.1N HCl, using phenolphthalein as an
indicator. A blank sample was also titrated for reference.
.
DS was calculated as
% ester: Vx-Vy×HCl normality× MM ester×10-3×100
Sample weight in gms
DS= 162×%ester .
MM ester×1000-(MMester-1×% ester)
Vx= volume in ml for blank
Vy= volume in ml for sample
MM ester= molecular mass of ester group
162 = molecular mass for glucose unit
40
3.4.7 Antioxidant potential
Antioxidant potential of Novel guar derivatives 120-124 was done by simple
calorimetric method. DPPH (2, 2-diphenyl-1-picryl hydrazyl) assay was used to
determine the antioxidant potential, by observing the decrease in DPPH radical
absorbance capacity at 517 nm by lee et al [120] spectroscopic method.
DPPH radical scavenging activity
0.005mL of Test compounds (120-124) were added into 0.095mL ethanolic solution
of DPPH dissolved in DMSO for making total volume upto 0.1mL (final
concentration of 100µM and 20 µM for DPPH and derivatives respectively).The
mixture was mixed vigorously on a vortex mixer and incubation was done for half an
hour in a water bath. for 30 min in a water bath at 37 °C. Control was 0.005mL of
DMSO instead of test compound and it was also placed in incubator with sample 96-
well tubes covered with parafilm to avoid evaporation for 30 minutes. UV- Visible
Spectrophotometer (UV-2800 Hitachi) was used to calculate decrease in absorbance
of the samples at 517 nm. All assays were done in triplicate. The activity was
explained as inhibition percentage. It was considered by means of the formula:
Radical scavenging activity (%) = [(Ax- Ay)/ Ax 100]
Where
Ax = Absorbance of blank,
Ay = Absorbance of sample.
41
SECTION II
3.5 Microwave assisted synthesis of guar gum derivatives via Acid
anhydride
3.5.1 A Synthesis of 126, 127, 128 (Method A)
A general method involves Mixing of 1.8 g (10 mmole sugar/30 mmol OH) of finally
ground purified partially hydrolyzed guar powder GG-2 and different concentration
of esterification promoter iodine. Three Different concentrations of acid anhydride
125A-125C (10, 20, 30 mmol) were added and mixed well to get a homogenous
mixture.
The mixtures were subjected to microwave heating/irradiation at different time
duration (5-15 min) with the interval of 30 seconds each, on the power level of 600.
Temperature was noted after every interval. Intermittent cooling was given to
normalize the temperature to attain the room temperature. Reaction Progress was
monitored by FTIR. After the required time of exposure (Maximum DS attain)
mixture was taken off and cooled to room temperature, washed several time with 50,
80, 90 % ethanol to remove unreacted acid followed by neutralization with 0.5N
NaOH soln to pH 7. Saturated aqueous sodium thiosulfate solution was added to the
reaction mixture to remove excess of iodine. Finally product was dried under
vaccume.
3.5.1 B Synthesis of Guar Derivatives (129-133) via cyclic anhydrides
(Method B)
A mixture of GG-2 (1.8 g, approximately 10m mol of anhydrosugar units), Three
Different concentrations (10, 20, 30 m mol) of finally powdered acid anhydride 125D-
125H, (0.5, 1.0, 1.5 equiv) of DMAP along with 5ml of DMSO was added to the
42
reaction flask and mix well to get a smooth Suspension. The system was subjected to
microwave irradiation at medium power level for different time intervals (5-15min).
After the requisite time period, the products were taken out, cooled to ambient
temperature and dispersed in water/ethanol mixture (50:50). The pH was adjusted to
7.0 of the resulting mixture with 0.5 M aqueous sodium hydroxide solution. The
product was washed several time with water/ethanol mixture (425), then with pure
ethanol and filtered under vacuum. The products were dried and powdered in a
mortar.
Filtrate was kept aside to determine total amount of anhydride consumed to know
about degree of substitution (DS) of modified derivatives (126-133)
3.5.2 Synthesis of Guar Acetate-GGAc (126)
DS: (calculated by titration) 2.64
Yield: % = 88.5
FTIR (KBr): cm-1 = 3250 (OH stretch), 2820 (C-H stretch), 1745 (C=O ester),
1235(C-O-C ester)
1HNMR (400MHz, D2O/DCl): δ ppm = 3.5-5.4 (sugar Protons), 2.03(3H, CH3-
Acetate)
43
3.5.3 Synthesis of Guar Propionate-GG-Pr (127)
DS: 1.33 (calculated by titration)
Yield =83.4 %
FTIR (KBr): cm-1= 3256 (OH stretch), 2830 (C-H stretch), 1743 (C=O ester), 1238(C-
O-C ester)
1HNMR (400MHz, D2O/DCl): δ ppm = 3.8-5.6 (sugar Protons), 2.14 (2H, 8-H2), 0.97
(3H, 9-H3);
3.5.4 Synthesis of Guar Butyrate- GGBu (128)
DS: 1.25
Yield =69.2%
44
FTIR (KBr): cm-1 =3412 (OH stretch), 2786(C-H stretch), 1726 (C=O ester), 1223 (C-
O-C ester)
1H-NMR (400MHz, D2O/DCl): δ ppm = 3.2-6.2 (sugar protons), 2.32 (2H, 8-H2),
1.43 (2H, 9-H2), 0.99 (3H, 10-H3);
3.5.5 Synthesis of Guar Succinate-GGSuc (129)
DS: 0.75
Yield =58.5 %
FTIR (KBr): cm-1 = 3318 (OH stretch), 2893 (C-H stretch), 1740(C=O ester), 1205
(C-O-C ester)
1H-NMR (400MHz, DMSO-d6): δ ppm = 3.2-6.2 (sugar protons), 2.73 (2H, 8-H2)
2.56 (2H, 9-H2);
45
3.5.6 Synthesis of Guar Maleate-GGMal (130)
DS: 0.45
Yield =65.4 %
FTIR (KBr): cm-1 =3415 (OH stretch), 2943 (C-H stretch), 1722 (C=O ester), 1225
(C-O-C ester)
1H-NMR (400MHz, DMSO-d6): δ ppm = 3.2-6.2 (sugar protons), 6.23 (2H, 8-H, 9-H)
3.5.7 Synthesis of Guar Phthalate- GG-Pht (131)
46
DS: 0.34
Yield =66.2 %
FTIR (KBr): cm-1 = 3312 (OH stretch), 2931 (C-H stretch), 1736 (C=O ester), 1252
(C-O-C ester)
1H-NMR (400MHz, DMSO-d6): δ ppm = 3.2-6.2 (sugar protons), 7.54-7.99 (Ar-H)
3.5.8 Synthesis of Guar Citraconate-GGCit (132)
DS: 0.65
Yield =80.2 %
FTIR (KBr): cm-1 =3546 (OH stretch), 2850(C-H stretch), 1712 (C=O ester), 1225 (C-
O-C ester)
1H-NMR (400MHz, DMSO-d6): δ ppm = 3.2-6.2 (sugar protons), 6.34 (1H, 8-H),
1.92 (3H, CH3)
47
3.5.9 Synthesis of Guar Glutarate–GGGl (133)
DS: 0.98 (Calculated by titration)
Yield =69.2 %
FTIR (KBr): cm-1 =3498 (OH stretch), 2943 (C-H stretch), 1744 (C=O ester), 1225
(C-O-C ester)
1H-NMR (400MHz, DMSO-d6): δ ppm = 3.2-6.2 (sugar protons), 2.12 (2H, 8-H2),
1.98 (2H, 9-H2), 2.30 (2H, 10-H2)
48
3.5.10 Quantitative Measurement of Degree of substitution of guar
esters
Unreacted anhydride and liberated acids (Filtrate) were titrated with 0.1 M NaOH
[121].
DS was calculated from amount of anhydride consumed which is equivalent to
amount of acid liberated.
Anhydride consumed (m mol) = (k /1000) (VCVx/Vy) eq(i)
k =mol equivalent weight of anhydride
V= volume (mL) of NaOH consumed
C = concentration of NaOH
Vy =volume of filtrate taken for titration
Vx = total volume of the filtrate
DS can be calculated by eq(ii)
DS=Anhydride consumed/K eq (ii)
Where K is the equivalent amount of anhydride consumed for a degree of substitution.
49
SECTION III
3.6 Heterogeneous Esterification of guar gum via fatty acid chloride
STEP: 1 Fatty Acid Chloride Synthesis
A general procedure involves refluxing of fatty acid (10mmole) with excess of thionyl
chloride 134 (20mmol) in the presence of catalytic amount of dry DMF (1-2 drops) on
a steam bath under inert atmosphere until the consumption of starting material.
Reaction was stopped after required time and the excess of thionyl chloride was
removed in Vacuo . Corresponding fatty acid chlorides [122] were obtained in the
form of Yellow oily liquid which was used without further purification. Elemental
Analysis confirmed formation of acid chloride.
STEP: 2 Fatty Acids Esters of guar (136-145)
Procedure of Peltonen et al [123] described in US patent 5589577 was used with
slight modification for esterification of GG-2 (110-4 mmol sugar unit/ 310-4 mmol
OH) with fatty acid chloride 135a- 135j (210-4 mmol) under inert atmosphere in
DMF and pyridine as a reaction promoter. Reaction Temperature varies from 100-140
°C for a different time intervals.
50
3.6.1 Synthesis of guar Valerate-GG-Val (136)
Valeryl chloride 135a (2.40g, 0.1mol,) was added dropwise to a solution of GG-2
(1.18g, 0.2 mol sugar) in dry DMF (50 mL) with catalytic amount of pyridine (~10
drops, cat.) under nitrogen. Reaction Mixture was stirred in an oil bath at reflux for 12
hours. When TLC indicated that all starting material had been consumed the reaction
was stopped and mixture was cooled to room temperature then extracted with 50%,
70% and 90% ethanol with vigorous stirring (3 x 25 mL). The product 136 was
filtered and dried in vacuo to give the product (93 %) as rubbery glue like solid.
Step: 1 Valeryl Chloride (135a)
EA: C, 48.81; H, 7.05; Cl, 30.39; O, 13.75
Step: 2 Synthesis of guar Valerate-GG-Val (136)
FTIR (KBr): cm-1= 3430 (OH stretch), 2928, 2830 (C-H stretch), 1754 (C=O ester),
1238(C-O-C ester)
1HNMR (400MHz, DMSO-d6/DCl): δ ppm = 3.8-5.6 (sugar Protons), 1.34-2.54(CH2-
Valerate), 0.97 (CH3-Valerate);
51
3.6.2 Synthesis of guar caproate/Hexanoate-GG-Hex (137)
A solution of hexanoyl chloride 135b (2.68g, 0.2 mol.) and gum (1.18g, 0.2mol) in
DMF (50 mL) were stirred at room temperature then pyridine (~10 drops, cat.) was
added and the mixture heated to 110 0C for 8 hours in an oil bath under nitrogen.
When TLC indicated the consumption of starting material reaction was quenched,
than extracted with ethano,l filtered and dried in vacuum to give the product 137 (75
%) as glue like solid.
Step: 1 Caproic Chloride (135b)
EA: C, 53.54; H, 8.34; Cl, 25.24; O, 12.88
Step: 2 guar caproate/Hexanoate -GG-Hex (137)
FTIR (KBr): cm-1= 3445 (OH stretch), 2938, 2825 (C-H stretch), 1754 (C=O ester),
1240(C-O-C ester)
1HNMR (400MHz, DMSO-d6/DCl): δ ppm = 3.8-5.6 (sugar Protons), 1.24-2.30(CH2-
caproate), 0.87 (CH3-caproate);
52
3.6.3 Synthesis of guar gum Heptanoate -GG-Hep (138)
Heptanoyl chloride 135c (2.96g, 0.1mol,) was added dropwise to a solution of gum
(1.18g, 0.2 mol sugar) in dry DMF (50 mL) with catalytic amount of pyridine (~10
drops, cat.) under nitrogen. Esterification procedure was same as above in example 1
to obtain product 138.
Step: 1 Heptanoyl Chloride (135c)
EA: C, 55.47; H, 9.92; Cl, 23.65; O, 10.96
Step: 2 Guar Heptanoate -GG-Hep (138)
FTIR (KBr): cm-1= 3398 (OH stretch), 2930, 2876 (C-H stretch), 1743 (C=O ester),
1240(C-O-C ester)
1HNMR (400MHz, DMSO6/DCl): ppm = 4.3-6.4 (sugar Protons), 1.35-2.33(CH2-
Heptanoate), 0.83 (CH3-Heptanoate);
53
3.6.4 Synthesis of Guar gum Caprylate /Octanoate -GG-oct (139)
Mixture of capric chloride 135d (3.26g, 110-4mmol,) and guar gum (1.18g, 210-
4mmol sugar) was added in dry DMF (50 mL) with small amount of pyridine under
nitrogen. Reaction Mixture was stirred in an oil bath at reflux for 10 hours. When
TLC monitoring indicated that all the starting material had been consumed the
reaction was stopped and mixture was cooled to room temperature then extracted with
50%, 70% and 90% ethanol: water (V/V) solution with vigorous stirring (4 x 25 mL).
The product 139 was filtered and dehydrated in vacuo to give the solid glue like
product.
Step: 1 Capric Chloride (135d)
EA: C, 60.07; H, 9.20; Cl, 20.69; O, 10.81
Step: 2 Guar caprylate/ Octanoate-GG-Oct (139)
FTIR (KBr): cm-1= 3470 (OH stretch), 2930, 2858(C-H stretch), 1760 (C=O ester),
1230(C-O-C ester)
1HNMR (400MHz, DMSO-d6/DCl): δ ppm = 3.6-5.4 (sugar Protons), 1.25-2.36(CH2-
caprylate), 0.85 (CH3-caprylate);
54
3.6.5 Synthesis of Guar gum Pelargonates -GG-Pel (140)
140 test compound was prepared by means of pelargonyl chloride 135e as described
in Example 1, the amount of 135e being (3.54g, 1 eq) per anhydrous sugar unit.
Step: 1 Pelargonoyl Chloride (135e)
EA: C, 61.20; H, 9.68; Cl, 21.07; O, 8.05
Step: 2 Guar Pelargonate/ Nonanoates -GG-Pla (140)
FTIR (KBr): cm-1= 3450 (OH stretch), 2930, 2950 (C-H stretch), 1740 (C=O ester),
1245(C-O-C ester)
1HNMR (400MHz, DMSO-d6/DCl): δ ppm = 3.6-5.6 (sugar Protons), 1.26-2.82
(CH2-pelargonate), 0.79 (CH3-pelargonate);
55
3.6.6 Synthesis of Guar gum Caprates/ Decanoates -GG-cap (141)
Caprylic chloride 135f (3.82 g, 0.2 mol, and 1 eq.), GG-2 (1.18g, 0.1 mol, 0.5 eq.)
and pyridine (3.5 g, 0.5 mol, 0.25 eq.) were refluxed in dry DMF (50 ml) under
nitrogen for a period of 6hrs (TLC indicated consumption of chloride). The solvent
was separated by vacuum filtration and the resulting white rubbery solid 141 was
washed with several times with different concentration of water: ethanol mixture
before extraction with 70% ethanol (3 x 50 ml).
Step: 1 Decanoyl Chloride (135f)
EA: C, 61.88; H, 11.14; Cl, 18.49; O, 8.49
Step: 2 Guar caprates/ Decanoates-GG-dec (141)
FTIR (KBr): cm-1= 3478 (OH stretch), 2930, 2845 (C-H stretch), 1753 (C=O ester),
1240(C-O-C ester)
1HNMR (400MHz, DMSO-d6/DCl
): δ ppm = 3.5-5.4 (sugar Protons), 1.24-2.33(CH2-caprates), 0.88 (CH3-caprates);
56
3.6.7 Synthesis of Guar Gum Lauroate -GG-Lau (142)
Lauroyl chloride 135g (4.38 g, 1.0 eq.) and GG-2 (1.18g, 0.5 eq.) in dry DMF (50 ml)
were stirred at 25°C inert atmosphere. Pyridine (10 drops, cat.) was added to the
homogenoized solution. The solution was refluxed at 140 oC and stirred for 3 hours.
The solvent was removed in vacuo and product 142 was washed and extracted with
70% (350ml) of Ethanol .pale yellow waxy ester 142 was dried and collected.
Step: 1 Lauroyl Chloride (135g)
EA: C, 65.78; H, 11.70; Cl, 15.18; O, 7.34
Step: 2 Guar Laurate -GG-Lau (142)
FTIR (KBr): cm-1= 3480 (OH stretch), 2976, 2845 (C-H stretch), 1743 (C=O ester),
1254(C-O-C ester)
1HNMR (400MHz, DMSO-d6/DCl): δ ppm = 3.5-5.4 (sugar Protons), 1.26-2.32(CH2-
laurate), 0.8 (CH3-laurate);
57
3.6.8 Synthesis of guar gum Myristate-GG-Myr (143)
Pyridine ((10 drops, cat.) was added dropwise to a stirred solution of Myristoyl
chloride 135h (4.94g, 0.2mol,0.5eq. ) and GG-2 (1.18g, 0.1mol, 0.5 eq.) in dry DMF
(50 ml) at 100oC under a nitrogen atmosphere. After required time period
(consumption of 135h indicated by TLC app 8hrs). The solvent was evaporated under
vaccume and purification by washing with different amount of acetone and ethanol.
Purified guar myristate 143 was obtained as a yellow waxy layer.
Step: 1 Myristoyl Chloride (135h)
EA: C, 69.10; H, 10.06; Cl, 13.29; O, 7.55
Step: 2 Guar Myristate -GG-Myr (143)
FTIR (KBr): cm-1= 3476(CH stretch), 2950, 2840 (C-H stretch), 1738 (C=O ester),
125o(C-O-C ester) 1HNMR (400MHz, DMSO-d6/DCl): δ ppm = 3.5-5.4 (sugar Protons), 1.26-2.32(CH2-
Myristate), 0.79(CH3-Myristate);
58
3.6.9 Synthesis of Guar Palmitate-GG-Pal (144)
Esterification procedure is same as above with palmitoyl chloride 135i (5.5g) which
corresponds to the molar amount of acid chloride used in general procedure to get
ester 144 in good yield.
Step: 1 Palmitoyl Chloride (135i)
EA: C, 69.70; H, 11.58; Cl, 10.90; O, 7.82
Step: 2 Guar Palmitate-GG-pal (144)
FTIR (KBr): cm-1= 3476(CH stretch), 2950, 2840 (C-H stretch), 1758 (C=O ester),
1250(C-O-C ester)
1HNMR (400MHz, DMSO-d6/DCl): δ ppm = 3.5-5.4 (sugar Protons), 1.26-2.34(CH2-
palmitate), 0.89(CH3-palmitate);
59
3.6.10 Synthesis of guar gum Stearate -GG-ste (145)
The reaction was performed in an oil bath while stirring, the mixture of (6.0g,
0.0002mmol) of Stearoyl chloride 135j and (0.18g, 0.0001g) of guar GG-2, few drops
of pyridine in dry DMF under inert atmosphere. temperature being 120.degree.C for 6
hours. After the completion of reaction the mixture was cooled to room temperature
and purified by extracting with water: ethanol solution several times to remove
unreacted by products. Purified white glue like ester 145 was filtered and dried.
Step: 1 Stearyl Chloride (135j)
EA: C, 69.70; H, 11.58; Cl, 10.90; O, 7.82
Step: 2 Guar Stearate -GG-Ste (145)
FTIR (KBr): cm-1= 3487(CH stretch), 2934, 2850 (C-H stretch), 1752 (C=O ester),
1245(C-O-C ester)
1HNMR (400MHz, DMSO-d6/DCl): δ ppm = 3.5-5.4 (sugar Protons), 1.23-2.75(CH2-
stearate), 0.83(CH3-stearate);
60
3.7 Determination of Degree of Substitution by, Heinze, Philipp,
Klemm
And Wagenknecht (1998) Method
0.15g Guar esters (136-145) were homogenized in 20ml of acetone-water (50:50%
v/v) mixture and kept for 24hours at room temperature with continuous stirring [124].
De-esterification was done by addition of 5ml (1M) ethanolic KOH solution and
mixture was kept for a day at room temperature .control sample was prepared without
guar ester. Then back titration of excess alkali (KOH) was back done with aqueous
HCl.
DS was calculated by following expression:
% Substitution = (Vblank VHCl) Mmsub MHCl 100
Wester
DS = 162 Mmsub
Mmsub (Mmsub -1) %Sub
Vblank = HCl volume used for blank values [ml] VHCl = Volume of hydrochloric acid [ml] Wester = Amount of guar esters (136-145) [g] MHCl = Molarityof hydrochloricacid [mol/l] Mmsub = Molar mass of substiuent [g/mol
61
SECTION IV
3.8 Testing Of Guar Gum Derivatives
3.8.1 Determination of Solubilities
The solubilities of the guar gum derivatives (120-124,126-133,136-145) were
determined in different organic solvents (Table 3.1) at concentration of (1% W/V),
with continuous stirring at RT and under heating.
Table 3.1 Types of solvents used for determination of Solubilities of guar
derivatives
No Solvent Abbreviation
1
2
Pyridine
N,N-dimethylformamide
PY
DMFA
3 Dimethylsulfoxide DMSO
5 Chloroform CCL4
6 Acetonitrile ACN
7 Dioxane DIO
8
9
Ethanol
Water
C2H5OH
H2O
3.8.2 Water Holding Capacity /Swelling Ratio of guar gum derivatives
The swelling equilibrium of synthesised (120-124,126-133,136-145) and native gum
(GG-1, GG-2) was carried out in triple distilled water. The precisely preweighed
samples (1 g) of each compound were dispersed in 50 ml of triple distilled water and
kept for 24 hours at 25°C (Japanese Industrial Standard K8150) to established
62
equilibrium swelling [125-127]. After required time, the samples were removed,
blotted with filter paper to remove excess water and filtered by a commercial sieve of
681μm (30 mesh)
The equilibrium degree of Swelling was measured by following expression (i)
Where,
SR = Wx-Wy Eq (i)
Wy
SR= Swelling Ratio
Wx = weight of sample after Swelling
Wy= Dry weight of sample before Swelling
Percentage of swelling (PS) was determined as
PS = SR100 Eq (ii)
3.8.3Gelation Study
O. S. Lawal et al. method [128] was used to determine the gelation properties of guar
derivatives. Modified samples of GG-1, GG-2 (2–15% w/v) were prepared in DMSO
(5mL). Continous stirring of mixture was done at 80°C for 30 min to form
homogeneous mixture followed by quick cooling at 4°C for 2 hrs. Least gelation
observed at that concentration when the sample did not fall down from the inverted
test tube.
63
Results &Discussion
64
4 RESULTS AND DISCUSSION
4.1 SECTION I
Novel Derivatives of Guar with Antioxidant Moieties
The current work emphasized on the fabrication of novel derivatives 120-124 of guar
gum GG-1 by replacing hydroxyl group of guar gum with different phenolic acids
Table 4.1 to introduce antioxidant moieties to guar backbone which can enhance its
application in pharmaceutical industry as a binder, disintegrators and as potential
carriers for targeted drug delivery [129, 130]
Table 4.1 Types of Phenolic Acid used for esterification
Compound No Phenolic Acid
118a
118b
118c
118d
118e
Cinnamic acid
t-Ferulic acid
Caffeic acid
p-Coumaric acid
Hydrocinnamic acid
Synthetic antioxidants have much concern due to toxicity but dietary fibers bounded
antioxidant has wide scope in medicines due to desirable drug release profile, cost-
effectiveness and non-toxicity [131]. Many researchers bounded antioxidant groups to
different nutritional fibers like Starch [132] ,cellulose [133] and dextran[134] etc But
no work done on guar gum due to its structural complexity, high molecular weight
and insolubility in any organic media. Taking into account the above procedures [135]
done on starch and cellulose this research described novel derivatives of guar gum
with antioxidant groups, bounded by reacting guar gum with cinnamic acid and its
analogues e.g. ferulic acid, p-coumaric acid, caffeic acid and hydrocinnamic acid by
in situ activation of acid with dicyclohexylcarbodiimide DCC (119) and N, N-
65
dimethylaminopyridine (DMAP) as a catalyst. Cinnamic acid and its derivatives
reveaedl strong antioxidant potential due to the presence of CH=CH-COOH group as
compared to other carboxylic acids [136]. Phenolic acid have been reported as good
free radical scavenger [137, 138]. Structure elucidation of guar esters were done by
FT-IR and1HNMR and SEM. Degree of substitution was done quantitatively by
titration method.
A novel route for synthesis of these esters via in situ activation of acids by coupling
with N, N'-dicyclohexylcarbodiimide (DCC) and DMAP has been reported here. It
replaced conventional method via acid chloride synthesis route. N, N’-
dicyclohexylcarbodiimide (DCC) act as dehydration agents and used to activate
phenolic acids towards ester formation. The reaction mechanism involves the
formation of intermediate O-acryl isourea by reacting acid with DCC. Free hydroxyl
group of GG attack reactive intermediate [139] and form corresponding ester and
DCU (dicyclohexyl urea) as a by-product (Stagelish esterification) as shown in
(scheme .4.1) and (scheme.4.2)
Effect of temperature, concentration of reactants and reaction duration was observed
for each experiment. Optimum reaction parameters were set for each derivative .it was
observed that efficiency of reaction is increased by increasing temperature and
reactant concentration. At room temperature no esterification was observed for 72h
probably it can be justified that at high temperature collision between reactant
increased to form a reactive intermediate.
Reaction is monitored by FTIR and TLC. Thin layer chromatography (TLC) was
another effective tool for the monitoring of reaction progress. Disappearance of DCC
during TLC analysis indicated the completion of reaction. Thin-layer chromatography
(TLC) analysis were carried out on silica gel 60precoated plates (Merck, Darmstadt,
W. Germany) with n-hexane: ethyl acetate (3:l) as a solvent and were developed by
spraying with 10% ethanol
66
Scheme 4.1 Esterification of GG-1 via in situ activation of Phenolic acid
67
Scheme 4.2 Reaction Mechanism for esterification of guar gum by insitu
activation of Phenolic acid with DCC, DMAP coupling Reactions
Purification of guar gum was done to remove insoluble impurities .The degree of
substitution was determined by acid base titration method. Detailed structure analysis
of native guar and its derivatives is prerequisite to know about synthetic paths and
products. FTIR spectroscopy is best tool for confirmation of esterification. There is
restriction for characterization of guar gum and its derivatives by NMR spectroscopy
due to high viscosity and polymeric structure of guar solution even at low
concentration as a result badly resolved spectra so careful acidic degradation or in situ
hydrolysis of guar gum in DCL is recommended.
68
4.1.1 Conversion of GG-1 via cinnamic acid 118a
GGC-120 was planned to synthesis via novel route from easily accessible starting
materials. Literature survey of prior synthetic methodology gave the initiative to play
with stagelish esterification. Reaction mechanism was carried out in two steps; first
step involved the formation of O-Acyl urea (Reaction intermediate) by reacting 118a
and DMAP.
Comparison of the FTIR and 1H-NMR spectra obtained for native GG-1 and GGC-
120 confirmed the esterification of guar. FTIR(KBr) spectra for Native guar gum
(Figure.2) showed broad band in a region of 3324cm-1 attributed to stretching
vibration of O–H bond which indicated the presence of large no of free hydroxyl
groups present in the molecule of guar backbone. The intensity of O-H bond was
reduced in modified esters of guar which showed large no of hydroxyl groups were
replaced by ester moieties. The finger print region of guar gum consisted of
characteristic peaks at 862 to 1145 cm-1, attributed to the C–O bond stretch. The
bands at 1636 cm-1 and 1376 cm-1were due to bending vibration of OH and CH2
respectively. The sharp band at 2926 cm-1 might be due to CH group stretching. A
sharp band for a carbonyl group appeared at 1723 cm−1 in the product 120 which was
enhanced in intensity with increase in DS value. The characteristic peak for C-O-C
stretch peculiar to esters appeared at 1213 cm-1.The appearance of two strong peaks at
2920 and 2840 cm-1 in the spectra of 120 was attributed to the methyl and methylene
C–H stretching coupled with the feruloyl moiety. In the GGC the broad peak around
3349 cm-1 was become sharp owing to the reduction in the number of free hydroxyl
groups in GG-1.
1H-NMR spectral data was adequately supporting the formation of compound 120.
Native Gum GG-1 showed resonance at (3.90 ppm) due to anomeric protons of
mannose back bone and resonance due to anomeric protons of galactose appeared at
(4.15 ppm) and its showed sharp peak as compared to mannose. A multiple appeared
between 2.5-3.5 ppm due to other sugar protons. Protons at position 8 and 7 showed
doublet at 6.3 and 7.02 ppm respectively. Multiplet between 6.56-6.94 ppm
69
attributed to aromatic ring protons of cinnamoyl group. After Successful synthesis of
120 other esters was designed by applying same synthetic protocols.
4.1.2 Conversion of GG-1 via trans-Ferulic acid 118b
The same route was employed for the homogeneous esterification of GG-1 with
118b. 1:1 equivalent of 118b and 119 were allowed to react with homogenous
solution of GG-1 in DMSO at 50°C for 72hrs under inert atmosphere to yield product
121 as white powder. The formation of the GGF was unambiguously confirmed by
FT-IR and 1H-NMR spectroscopy. Confirmation of esterification was done by FTIR
which indicated the formation of ester bands at 1732 and 1238 cm-1 respectively due
to C=O and C-O-C stretching vibrations. Band appeared at 3415cm-1 due to O-H
stretch reduced in intensity.
1H-NMR spectra showed multiplet between 3.8-5.4 ppm due to sugar protons of guar
backbone and singlet appeared at 3.8 ppm due to methoxy protons of 118b. Broad
singlet at 4.19 ppm might be due to OH proton. Downfield doublet at 6.17 and 7.40
ppm indicated the presence of vinylic protons in ferulic acid and the aromatic ring
protons were observed in the range of 6.74–7.02 ppm.
4.1.3 Conversion of GG-1 via Caffeic acid 118c
An attempt was made to covalently bounded Caffeoryl group to guar gum. The
homogenous esterification was applied by in situ activation of 118c , 119 ,GG-1 in
dry DMF under nitrogen for 48hrs (Maximum DS obtained ) at 70°C. No considerable
change occurred at 50° for 72 hrs so temperature was increased to get guar ester 122
in good yield with maximum DS of 0.69 calculated by titration. Reaction duration
was reduced due to increase in temperature from 72 to 48 hrs. The efficiency of
reaction was monitored by TLC until its finishing point. By product dicyclohexyl urea
was removed by washing with hot aliquots of methanol, diethyl ether and chloroform
to achieved required ester 122 as a pale yellow solid.
FTIR spectra confirmed the targeted compound 122. A sharp band for a carbonyl
group appeared at 1729 cm−1 in the GGCa. Absorption band at 1219 cm−1 confirmed
presence of C-O-C stretch particular for esters.
70
Proton NMR data supported the information revealed by FTIR data. The behaviour
of sugar protons in guar was same as in 120 and 121 esters. The peak pattern in 1H-
NMR showed doublet at 6.91 and 7.60 ppm for vinylic protons of caffeoryl group.
Singlet appeared at 5.35 ppm showed presence of OH group in 118c. Multiplet at
6.93 ppm confirmed the successful synthesis of product 122.
4.1.4 Conversion of GG-1 via p-Coumaric acid 118d
Coumaroyl moiety was directly linked on the free hydroxyl group of GG-1 by
Stagleish esterification of 118d with DCC, DMAP coupling reaction. Various trail
attempts were made to synthesis compound 123 using different concentration of
reactants at 50°C in DMSO but no esterification occurred. Reaction Mixture was
heated to reflux for approx 72hrs until the disappearance of starting material
confirmed by TLC. Product was obtained in low yield due to the formation of
unnecessary side product.
IR spectra showed slight broad absorption at 3335 cm-1 due to the presence of large
excess of free hydroxyl groups. DS calculated by titration was 0.039 which indicated
that large excess of free unsubstituted hydroxyl groups were still present. Carbonyl
signal with low intensity appeared at 1729 cm-1 which confirmed formation of ester
with low DS value. 1HNMR showed peaks at 3.2- 5.4 due to guar protons. Proton 7
and 8 showed set of doublet at 7.41 and 6.13 ppm respectively. Pair of doublet
appeared at 6.65 & 7.32 ppm due to aromatic ring protons associated with coumaric
acid. Singlet at 5.32 ppm might be associated with OH groups of coumaroyl
substituent.
4.1.5 Conversion of GG-1 via Hydrocinnamic acid 118e
The esterification of 118e with GG-1 resulted higher reaction yield with greater DS
value upto 2.34. Reaction followed the same protocols as stated above using DCC as
in situ activator with DMAP in DMSO with 118e which reacted with OH-groups of
guar. Reaction completed in 24hrs. Hydrocinnamic acid with saturated side chain
71
yield product 124 with good yield and degree of substitution as compared to products
120-123 which might be due to electronic and stearic effects associated with double
bond.
IR Spectral Data showed two characteristic sharp peaks at 1723 & 1250 cm-1 due to
C=O and C-O-C stretch typical for esters. The protons of acid group appeared at 2.53
(7-H), 2.89 (8-H), 7.29 (Ar-H) ppm. These Results for structure analysis was in good
agreement with desired product 124.
4.1.6 Antioxidant Assay of Guar Derivatives 120-124
Our body generated variety of free radicals during biochemical processes especially
when oxygen is consumed for energy production. Normally there is check in balance
between production and consumption of free radicals. But some time due to certain
external and internal factors excess of free radicals are shaped in our body, being
highly reactive, they can cause damage to biomolecules e.g. protein, carbohydrate ,
DNA, amino acids etc and causes a degenerative diseases such as arteriosclerotic
vascular disease (ASDV), inflammation, cancer, asthma and diabetes and premature
ageing. Living organism have very sophisticated “antioxidant Defence system’’ which
comprises of variety of endogenous and exogenous compounds .These compounds
prevent body from oxidative stress created by free radicals. Antioxidants soak up
these free radicals and enable the cells to invigorate for life process.
The common antioxidants are vitamins A, B, C & E, carotenes, ascorbic acid,
selenium etc are available naturally. Their free radical scavenger ability mainly
depends upon phenolic contents incorporated in their structure. Many synthetic
antioxidants are commercialized such as propyl gallate (PG), Dihydroxy flavones
(DHF), Butylated hydroxylanisole (BHA), Butylated hydroxyl toluene (BHT) etc.
Synthetic antioxidants have much more concern due to poor pharmacokinetics effects.
For these reasons linkage of natural biopolymers with antioxidant molecules leads to
improvement in their properties.
72
4.1.7 DPPH Assay
DPPH is abbreviated as 1, 1-diphenyl-2-picrylhydrazyl is a stable free radical that has
ability to readily accept an electron to convert into diamagnetic stable molecule. Its
radical scavenger capacity was determined by decrease in absorbance at 517 nm due
to the transformation of DPPH into DPPH• with change in color from dark violet to
yellow. DPPH method is an easy calorimetric method used for measurement of
antioxidant potential of variety of natural compounds. It is accurate, valid, economical
sensitive methodology for evaluation of free radical scavengering activity of variety
of naturally occurring compounds e.g. cinnamic acids and its derivatives. Biological
activities of cinnamic acid and derivatives are well proved by many researchers [140].
Scheme 4.3 Reaction mechanism of DPPH
4.1.8 Radical Scavenging studies of DPPH
Radical Scavenging potential of DPPH was studies for test compounds 120-124.
Faster reaction was observed for Phenolic acids (118a-118e) as compared to their
derivatives. Guar esters showed significant radical scavenging potential at almost all
concentration. The activity increased by increasing amount of test compound and by
increasing DS value of sample. Maximum Scavenging was observed for compound
73
122 and compound 124 proved to be inactive. Minimum Scavenging was noticed for
compound 123 and at lower DS it is also showed inactivity. Result is summarized in
Table 4.2.
Table 4.2 Radical Scavenging activity of compounds 120-124
Sample Radical Scavenging activity (%)
118a 28.45±0.45
118b 23.15±0.91
118c 45.6±0.67
118d 7.0 ±0.32
118e 2.4.±0.8
120 18.3±0.9
121 18.43±0.5
122 30.23±0.7
123 2.32±0.5
124 Inactive
74
Figure 4.1A
Figure 4.1B
Figure 4.1 comparison of antioxidant potential of phenolic acids and their esters
28.45
23.15
45.6
7
2.4
118a 118b 118c 118c 118e
Radical Scavengeing activity (%)
0
18.3 18.43
30.23
2.320
control 120 121 122 123 124
Radical Scavengeing activity (%)
Y‐Values
75
4.2 SECTION II
Novel Route for synthesis of guar derivatives by microwave
irradiation
Microwave-assisted synthesis (MAS) of polysaccharides esters is a green way of
synthesis different valuable biopolymers which eliminate danger to health and an
environment .MAS technique for polysaccharides has attracted considerable attention
in recent years and polysaccharide chemistry has achieved extensive improvement
from microwave irradiation. So the implementation of fast, expeditious and cost-
effective methodologies [141] for the modification of polysaccharides has become a
prerequisite. With this aim, this section emphasized on the synthesis of green, cost
effective derivatives of guar gum via novel protocols by reacting guar gum with
variety of anhydrides using iodine and DMAP. A new method for esterification of
guar gum under microwave heating has been introduced to replace laborious and time
consuming conventional method [142].
Extensive work has been done on Microwave induced esterification of starch [143]
and cellulose [144] derivatives but very inadequate work is done on galactomannan
(e.g. guar gum) due to its structure complexity and high molecular weight. Limited
papers about esterification of guar gum by acid anhydride are reported by
conventional methods like M.R. Savitha Prashanth at el (2006) [113] prepared
Acetate, succinate and octenylsuccinate derivatives of guar using NaHCO3 as
catalyst. Rumiko Fujioka, Yukari Tanaka, Toshio Yoshimura (2009) [114] investigated
the Synthesis of novel superabsorbent hydrogels with the reaction of guar gum and
succinic anhydride (SA), using of 4-dimethylaminopyridine as a catalyst .M. A.
Shenoy, D. J. D’Melo (2010) [115] acetylated hydroxyl propyl guar to use as a filler
in polyester composite by acetic anhydride and pyridine. Esterification of hydrolyzed
guar and gum Arabic with n-octenyl succinic anhydride and oleic acid was done by
Shatabhisa Sarkar, Rekha S. Singhal(2011) [116] but no considerable work is done on
guar gum esters via anhydride by microwave heating.
76
A more recent method involved dissolution of the Guar gum in anhydrous DMSO
followed by treatment with catalyst and acid anhydride to form desirable derivatives
of guar gum with different degree of substitution. DMF and DMSO were considered
good solvent for Microwave heating with high boiling point and imparted no
hazardous effect on the polymer. Iodine was used as a novel, efficient, economical
and convenient catalyst [145] used for esterifiication of 126-128 (Scheme 4.4) as
compared to other catalyst such as perchloric acid, sulfuric acid, pyridine,
triethylamine etc. Many researchers reported solvent free or solvent less iodine
catalyzed etherification of polysaccharides as an efficient and green methodology
[146-148] but not even a single paper was reported with solvent free esterification of
guar gum catalyzed by iodine, so iodine was proved as novel, efficient and strong
catalyst for production of variety of guar esters by microwave heating. A plausible
mechanism involves the ionization of iodine into corresponding ions I+ and I-,
which in turn activates carbonyl groups and converted into acylating agents which
further reacted with GG-2 to form guar esters 126-128 with good yield and DS
values. This method reduces amount of solvent so economical and environmentally
friendly.
R=CH3, -CH2CH3, -CH2CH2CH3
Scheme 4.4 Iodine Catalyzed esterification of GG-2 via Acetic, Propionic and
butyric anhydride
77
In (Method-2) DMAP was used a reaction promoter for synthesis of modified gums
129-133 (Scheme 4.5). Reaction mechanism involved the nucleophilic attack of
catalyst on carbonyl carbon of acid anhydride [149] which leads to intermediate
formation. Intermediate reacted with free hydroxyl groups of GG-2 to produce guar
esters 129-133 with different DS values.
Scheme 4.5 N, N-dimethylaminopyridine Catalyzed esterification of GG-2 via
Phthalic anhydride
78
By this method, it was not achievable to completely substitute the free hydroxyl
groups of guar by using 1:3 molar ratio of GG/anhydride at medium power level for
15 min. However, organo soluble products was obtained, which yielded better
resolved 1H NMR spectrum. The incomplete substitution of gum might be due to less
reactivity of cyclic anhydrides as compared to aliphatic anhydride [150-154].
Variable studied were concentration of reactants and catalyst along with time
intervals. The reaction was confirmed by FTIR, which showed the formation of ester
group. Chemical structure changes were assessed by variation in physical properties
such as solubility, rheological study, swelling behaviour, gelation etc. A change in
surface was studied by SEM images. Further Structure elucidation was done by 1H-
NMR.
4.2.1 Acetylation of GG-2
Acetylation of Polysaccharides has been documented from decades [155-157]. Iodine
was considered as good reagent for microwave energy absorber so an approach
reported by Biswas et all. and many other researchers was applied for esterification of
guar gum. Product 126 was obtained by heating ground material GG-2 with acetic
anhydride and iodine. The results appreciably confirmed the efficiency of this method
with almost complete substitution under solvent free-conditions. Proton NMR
confirmed peaks at 3.5-5.4 ppm correspond to sugar protons. The methyl protons of
the acetyl moieties resonate at 2.03 ppm. A distinctive ester peak appeared at 1745
cm–1 in FTIR spectrum of product 126 which confirmed esterification of hydroxyl
groups of guar. Absorption peak at 3300 cm–1 due to hydroxyl group was almost
vanished which indicated that maximum no of hydroxyl was substitutes with acetate
moieties.
4.2.2 Guar propionate (127) and guar butyrate (128) synthesis
Because the results obtained for 126 were encouraging so an attempt was made to
employed same method for the production of compound 127 and 128. Observed yield
and substitution values for these products was low as compared to 126 this might be
attributed to the lower reactivity of propionate and butyrate anhydrides as compared
79
to acetic anhydride.1H-NMR spectrum showed resonance at 2.14 and 0.97 ppm due to
the methylene and methyl protons of propionate group respectively. Proton spectra for
the 128 products were to some extent more complicated. Methyl group of butyl
moieties showed resonance at 0.99 ppm and methylene protons resonated at 2.32 &
1.43 due to H-8 and H-9 respectively. All of the expected peaks due to anhydro sugar
units were apparent in the samples. IR Spectral Data showed characteristic sharp
peaks at 1743 & 1726cm-1 due to C=O bond 127 & 128 respectively typical for ester
groups. Reaction conditions were summarized in table 4.2.
4.2.3 Microwave assisted synthesis of Guar esters via cyclic anhydride
In this method GG-2 was allowed to react with acid anhydride (125D-125H) by
using 4-dimethylaminopyridine as a reaction promoter and dimethylsulfoxide
(DMSO) as a reacting media (Scheme 4.5). To reduce the activation energy and to
enhance the functionality of free hydroxyl groups of guar, an appropriate solvent and
catalyst plays an important role. DMSO was proven best solvent for microwave
heating due to greater dielectric constant which enhanced its capacity to absorb
microwave irradiation to attain higher temperature. Mostly for esterification of
hydroxyl pyridine and DMAP were considered as effective basic catalyst. As
compared to pyridine, DMAP has superior stability and higher basicity [158]. So it
was considered basic catalyst for esterification of variety of polysaccharides in recent
years. The mechanism of esterification via DMAP was considered to be nucleophilic
substitution reaction (scheme 4.5). In this substitution mechanism cyclic anhydride
reacted with catalyst to form anhydride pyridinum intermediate which in turn attack
OH groups more easily as compared to cyclic anhydride. In the next sequence of
catalyzation DMAP was eliminated due to affinity of OH groups to bond with
carboxyl group.
FTIR spectroscopy is most valid technique used for characterization of guar esters
129-133.Compared to spectrum of autochthonic gum (GG-2) and esters (129-133)
presence of the typical ester peaks at 1740, 1722, 1736, 1712, 1744 cm-1 is a proof of
esterification. Moreover intensity of absorption band due to OH stretch around 3600-
3300 cm-1 was decreased and intensity of C-O-C symmetrical stretching in esters at
80
1225 cm-1 (approximate) was increased. Peak around 1517, 1570, 1571, 1560, 1578
cm-1 appeared in FTIR spectrum of compound 129-133 respectively due to
antisymmetric stretching of carboxylic anions .No peaks were observed due to
unreacted anhydride. These changes confirmed induction of carboxylic and succinate,
maleate, phthalate, citraconate, glutarate groups in guar backbone.
Table 4.3 Microwave assisted esterification of guar via aliphatic anhydride
Sample
No
moleq of
Anhydride/
•ASU
Time
(Min)
DS
Yield %
(Guar ester)
126-A
126-B
126-C
126-D
126-E
126-F
126-G
126-H
126-I
127-A
127-B
127-C
1:1
1:1
1:1
2:1
2:1
2:1
3:1
3:1
3:1
1:1
1:1
1:1
5
10
15
5
10
15
5
10
15
5
10
15
0.15
0.11
0.16
0.21
0.99
1.33
1.75
2.43
2.64
-
0.093
0.09
88.2
87.4
87.3
84.2
85.4
87.5
76.5
69.2
58.5
98.3
95.4
89.2
81
127-D
127-E
127-F
127-G
127-H
127-I
128-A
128-B
128-C
128-D
128-E
128-F
128-G
128-H
128-I
2:1
2:1
2:1
3:1
3:1
3:1
1:1
1:1
1:1
2:1
2:1
2:1
3:1
3:1
3:1
5
10
15
5
10
13.5
5
10
15
5
10
15
5
10
15
0.13
0.23
0.74
0.98
1.15
1.33
-
-
0.056
0.08
0.095
0.17
0.25
0.98
1.25
88.4
87.4
87.3
75.6
77.2
65.4.
90.3
92.3
84.4
83.2
86.4
88.4
79.4
68.7
53.2
DS: Determined By Titration Method •ASU = Anhydrous sugar
Unit
82
OORO O
O
O
O
OH
OORO O
O
O
O
OH
OORO O
O
OH
OO
OORO
OR
O
O
O
O
OH
OORO
OR
O
O
O O
OH
OROR
OR
129
130131
132133
OOHO O
OH
OH
GG-2
MW
MW
MW
MW
MW
125E
125D
125F
125G
125HDMAP
DMAP
DMAP
DMAP
DMAP
Scheme 4.6 Microwave assisted guar esters synthesis via cyclic anhydride
For the verification of structural changes samples were characterized by 1H-NMR
spectroscopy. Resonances assigned to proton atoms of succinate ester moieties were
appeared at 2.73 (8-H2) 2.56 (9-H) ppm. Sugar protons resonate at 3.2-6.2 ppm.
The signals due to H-8 & H-9 in guar maleate (130) appeared at 6.23 ppm. The
spectrum showed signals at 7.54-7.99 ppm due to aromatic protons of phthalate
moieties. Peak at 6.34 ppm due to proton at position 8 appeared in spectrum of
compound 132, methyl group of citraconate moieties showed resonance at 1.92
ppm. Product 133 showed well resolved spectra in DMSO-d6 .Resonances appeared at
2.12 (8-H), 1.98 (9-H) and 2.30 (10-H) ppm due to glutarate group. Reaction
conditions were summarized in Table 4.4.
83
Table 4.4 Microwave assisted esterification of guar via cyclic anhydride
Sample
No
moleq of
Anhydride/
sugar
Time
(Min)
DS
Yield %
(Guar ester)
129-A
129-B
129-C
129-D
129-E
129-F
129-G
129-H
129-I
130-A
130-B
130-C
130-D
130-E
130-F
1:1
1:1
1:1
2:1
2:1
2:1
3:1
3:1
3:1
1:1
1:1
1:1
2:1
2:1
2:1
5
12.5
14.5
3.5
10
15
4
9.5
12.5
5
10
15
5
10
13.5
-
0.012
0.056
0.054
0.074
0.12
0.34
0.68
0.75
-
-
0.011
0.024
0.034
0.074
88.2
87.4
87.3
84.2
85.4
87.5
76.5
69.2
58.5
98.3
95.4
89.2
88.4
87.4
87.3
84
130-G
130-H
130-I
131-A
131-B
131-C
131-D
131-E
131-F
131-G
131-H
131-I
132-A
132-B
132-C
132-D
132-E
132-F
132-G
132-H
132-I
3:1
3:1
3:1
1:1
1:1
1:1
2:1
2:1
2:1
3:1
3:1
3:1
1:1
1:1
1:1
2:1
2:1
2:1
3:1
3:1
3:1
5
10
15
5
10
15
5
10
15
5
10.5
15
5
10
15
5
12
14.5
5
10
15
0.094
0.13
0.45
0.01
0.022
0.017
0.034
0.056
0.076
0.098
0.16
0.34
0.001
0.023
0.045
0.054
0.074
0.13
0.33
0.29
0.65
75.6
77.2
65.4
90.3
92.3
84.4
83.2
86.4
88.4
79.4
68.7
66.2
90.2
89.6
87.4
87.4
88.2
85.4
74.5
77.3
80.2
85
133-A
133-B
133-C
133-D
133-E
133-F
133-G
133-H
133-I
1:1
1:1
1:1
2:1
2:1
2:1
3:1
3:1
3:1
5
10
15
5
10
15
5
12
15
0.003
0.023
0.034
0.044
0.099
0.12
0.54
0.98
0.87
90.2
91.6
87.5
88.4
87.4
79.4
76.5
69.2
68.7
DS: Determined By Titration Method •ASU =Anhydrous sugar unit
4.2.4 Optimization of Reaction Conditions
Reaction conditions were optimized for each experiment to attain product with better
yield and substitution ratio. Variable studied were time interval, amount of catalyst
and concentration of reagents used. An attempt was done to introduce speedy,
economical and rapid MAS technique for the modification of guar esters via acid
anhydride by varying the reaction variables. When GG-2 was reacted with 3equiv of
acid anhydride without any catalyst for 15 minutes no reaction was observed. By
increasing the amount of iodine and DMAP there was pronounced effect on DS value
of samples. It was cleared that substitution degree increased by increasing catalyst
but the yield of reaction decreased.
86
Table 4.5 Effect of concentration of iodine on DS value
Sample No Moleq
Anhydride/
Sugar unit
Iodine
meq/sugar unit
DS
126-J
3:1
0.25
1.23
126-K 3:1 0.50 2.43
126-L 3:1 0.75 2.42
127-J 3:1 0.25 0.87
127-K 3:1 0.50 1.15
127-L 3:1 0.75 1.23
128-J 2.5:1 0.50 1.11
128-K 2.5:1 0.75 0.94
128-L 2.5:1 1 1.15
129-J 3:1 0.25 0.58
129-K 3:1 0.50 0.56
129-L 3:1 0.75 0.68
130-J 3:1 0.50 0.23
130-K 3:1 0.75 0.45
130-L 3:1 1 0.45
131-J 3:1 0.25 0.15
131-K 3:1 0.50 0.23
131-L 3:1 0.75 0.34
132-J 2.5:1 0.50 0.45
132-K 2.5:1 0.75 0.63
132-L 2.5:1 1 0.65
133-J 2:1 0.75 0.67
133-K 2:1 1 0.76
133-L 2:1 1.5 0.98
87
Thus, there were optimal levels of iodine depending on the required DS value as
shown in table 4.5. For product 126 experiments was run in triplicate by keeping time
of reaction (15min) and molar concentrations constant. Product 126J, 126K, 126L
gave DS 1.23, 2.43, 2.42 respectively in the presence of different amounts of iodine.
However DS was decreased by increasing amount of iodine above 0.75 equiv. It
appeared that excess amount of catalyst has no effect on DS and might hydrolysing
the ester. Similar results were manipulated for other compounds 127-133 with slight
variation.
The reaction time was set 15 min for each experiment. Reaction time has considerable
effect on efficacy of reaction because prolong time of exposure increases the
absorption of reactants between anhydride and gum. However further increase in
reaction time decreased the substitution ratio which might be due to cleavage of ester
bonds. So 10-15 minutes were optimum reaction time to obtain product with higher
DS values and greater yield. Table 4.6 showed linear relationship between time
interval and substitution value by keeping catalyst amount constant 0.25 equivalent
per anhydrosugar unit. Three different experiments were carried out for product 126
in the presence of 0.25 equiv iodine and 3 equiv of acetic anhydride for different time
intervals (5, 10, 15 min). Resultant samples 126M, 126N & 126O gave DS of 0.87,
1.07, and 1.23 respectively. However above 15min there was no further enhancement
of substitution value. Same result was obtained for other compounds with little
variation. Product 128 showed no substitution within 5 min for 128-M, 0.34 within
10min for 128-N than decrease in DS 0.23 within 15 min for 128-O. By increasing
time, reaction temperature was also increased which provided a positive collisions
between acid anhydride and OH groups. But further increase in temperature degraded
gum structure and hydrolysis of ester bond along with production of by products.
88
Table 4.6 Linear relationship between time interval of Microwave heating & DS
values
Sample No Moleq
Anhydride/
Sugar unit
Time
(Minutes)
DS
126-M
3:1
5
0.87
126-N 3:1 10 1.01
126-O 3:1 15 1.23
127-M 3:1 5 0.33
127-N 3:1 10 0.99
127-O 3:1 15 1.11
128-M 2.5:1 5 -
128-N 2.5:1 10 0.34
128-O 2.5:1 15 0.23
129-M 3:1 5 -
129-N 3:1 10 0.012
129-O 3:1 15 0.68
130-M 3:1 5 0.01
130-N 3:1 10 0.23
130-O 3:1 15 0.45
131-M 3:1 5 0.03
131-N 3:1 10 0.23
131-O 3:1 15 0.34
132-M 2.5:1 5 -
132-N 2.5:1 10 0.33
132-O 2.5:1 15 0.65
133-M 2:1 5 -
133-N 2:1 10 0.76
133-O 2:1 15 0.98
89
Table 4.7 Effect of Acid anhydride concentration on Degree of Substitution
Sample No Iodine
meq/sugar unit
Moleq
Anhydride/
Sugar unit
DS
126-P
0.75
1:1
1.87
126-Q 0.70 2:1 2.23
126-R 0.75 3:1 1.96
127-P 0.75 1:1 0.33
127-Q 0.75 2:1 1.23
127-R 0.75 3:1 1.24
128-P 0.75 1:1 0.23
128-Q 0.75 2:1 0.99
128-R 0.75 3:1 1.23
129-P 0.75 1:1 0.023
129-Q 0.70 2:1 0.64
129-R 0.75 3:1 0.73
130-P 0.75 1:1 -
130-Q 0.75 2:1 0.45
130-R 0.75 3:1 0.045
131-P 0.75 1:1 0.54
131-Q 0.75 2:1 -
131-R 0.75 3:1 0.34
132-P 0.75 1:1 -
132-Q 0.75 2:1 0.33
132-R 0.75 3:1 0.65
133-P 0.75 1:1 0.04
133-Q 0.75 2:1 0.97
133-R 0.75 3:1 0.84
90
The reason for highest efficiency of reaction at higher concentration was due to larger
interaction of reacting species, greater no of molecules of carboxylic groups were
available to replace hydroxyl group of gum.
At optimal reaction conditions reaction mixture become homogenous and transparent
which showed homogenous distribution of anhydrides in the gum granules. Diffusion
Concentration of acid anhydride has linear effect on degree of substitution of gum.
Three different concentrations (10, 20, 30mmole/sugar unit) of acid anhydride was
irradiated by keeping reaction time (15 min) same for each trial in the presence of
0.75 equivalent/sugar unit of catalyst. The highest DS obtained for sample no 126-Q
was 2.23 with 20mmole acetic anhydride. Samples 127-R, 128-R, 129-R, 130-Q, 131-
P, 132-R, 133-Q gave maximum DS of 1.24, 1.23, 0.73, 0.45, 0.54, 0.65, 0.97
respectively with similar reaction conditions
Reaction mechanism played a vital part in making the inner OH group available to the
reaction with anhydrides. At the start reaction was heterogeneous and the OH group
on the surface of gum was preferentially modified but with a passage of time the gum
dissolved in the reaction mixture at higher temperature due to prolong heating. As a
result other inner OH groups were also modified subsequently. We concluded that
microwave induced esterification of GG-2 is a promising method which can enhanced
thermoplastic, mechanical and morphological properties to Gum [159]. This method
did work well for esterification of other biopolymers such as starch, cellulose and
galactomannan.
91
4.3 SECTION III
Esterification of Cellulose with Fatty acids via acid chloride Route
An interesting methodology is reported in this section for modification of
Autochthonic Guar (GG-2) by reacting hydroxyl groups of mannose and galactose
with variety of fatty acids chloride (Table 4.8) ranging from C5-C18. A series of fatty
acid esters were obtained by this method with variable DS values and physical
properties.
Table 4.8 Types of Fatty acid chlorides used for fabrication of Novel derivatives
(136-145)
Sample no Name of
Acid chloride
Structure
135a
Valeryl chloride
135b
Caproic chloride
135c
Heptanoyl Chloride
135d
Caprylic chloride
92
135e
Pelargonic chloride
135f
Capric chloride
135g
Lauroyl chloride
135h
Myristoyl chloride
135i
Palmitoyl chloride
135j
Stearoyl Chloride
93
Unsaturated fatty acids have a valuable influence on the human health but it cannot be
used directly as food additives in their native form. Derivatives of guar-fatty acids
might be an interesting substitute of fatty acids. Long chain fatty acid derivatives of
polysaccharides have been intensively studied by many researchers [160-163]. Green
thinking emphasized on creating such environmental friendly biopolymers with
promising properties such as thermoplasticity, emulsification etc. The commercial and
academic scientist thoroughly studied synthesis of fatty acid esters of cellulose [164],
starch [165] and many other polysaccharides [166]. Products have extensive
applications in food and non-food industries. However the knowledge of the higher
fatty acid esters of guar is limited. By critically reviewed the literature only one paper
reported by Dong et all. described the preparation of palmitoylated guar
galactomannan (PGGM) with good yield and emulsifying properties. No considerable
work has been done to prepare long chain fatty acid esters of guar by heterogeneous
conditions. For fulfilling this gap the research described in this section had a purpose
to the preparation of series of fatty acid esters (C5-C18) by acid chloride-pyridine
method [167].
Acyl chlorides are useful as reactive intermediates and are used in numbers of organic
transformation. Different methods are reported for production of acid chlorides. First
step involved the preparatory methods for synthesis of acid chloride by refluxing fatty
acids with slight excess of thionyl chloride (Scheme 4.7). More Convenient way for
synthesis of fatty acid chloride was employed here by reacting fatty acid with thionyl
chloride to yield acid chloride, sulphur dioxide and hydrogen chloride. The separation
of by products was very simple and done by distilling the mixture to remove excess of
acid or sulphur dioxide to from acyl chloride. The product was analyzed by elemental
analysis [168].
94
Scheme 4.7: Proposed Mechanism for synthesis of fatty acid chloride
In second step GG-2 was dissolved in DMF which ensured homogeneous substitution
by enhancing accessibility of reactants then it was allowed to react with 2 mole
equivalent of carboxylic acid chloride along with catalytic amount of pyridine under
inert atmosphere for different time interval at 100-140°C. Reaction could proceed
without additional base pyridine but products obtained had poor yield and substitution
pattern along with time required for completion is prolong [169]. To avoid moisture
(acid chloride reacts vigorously with H2), the acid chloride was reacted directly in
Step 2 (Scheme 4.7).
A range of diverse guar esters was successfully prepared via this path (Scheme 4.8),
however, with the use of an additional base pyridine. Taking into account these results
the reaction conditions (time, molar ratio of the reagents and the appliance of an
95
additional base, e.g. pyridine) were optimized (Table: 4.9) for each sample to obtain
product with maximum yield. Guar esters (136-145) showed two featured peaks in
FTIR spectra typical for the ester moieties due to C-O-CEster, C=OEster vibrations. The
absence of absorption bands around 1800 cm-1 and 1700 cm-1 in all spectra indicated
the absence of any unreacted acyl chloride and carboxylic acid. Relative to the O–H
absorbance the intensity of the C–H stretching bands enhanced with increasing acid
chain length in FTIR spectra. Further structural elucidation was done with 1H-NMR.
These guar derivatives possessed different solubility, viscosity, and gelation ability,
water holding capacity and viscosities as compared to native gum. Remarkable
changes in physical properties was observed which depending upon chain length of
carboxylic acid and substitution degree. It was demonstrated that extent of reaction
depends upon reactivity of acid chloride, which in turn increased with chain length of
fatty acid [170]. Greater the DS value greater is organo soluble capacity. Surface
changes were confirmed by SEM imaging which showed more networking in
derivatives as compared to native one.
96
Scheme 4.8: Schematic Plot of the conversion of Guar gum with fatty acids
Via Acid chloride-pyridine route
97
Table 4.9 Conditions and Results of guar esterification mediated by Acid
chloride-pyridine Route
a) = DS calculated by Titration Method
4.3.1 Fatty acid chloride synthesis and characterization by elemental analysis
Towards the synthesis of guar esters via fatty acids the first step was synthesis of acid
chloride by reacting 10 mmole of acid with slight excess of thionyl chloride.
Elemental analysis was used to confirm the formation of acid chloride. Elemental
analysis showed the absence of sulphur and presence of chlorine (Table: 4.10).
Reaction mechanism involved the attack of carboxylic acid to electophilic sulphur to
form highly unstable reactive intermediate. Which in turn attach HCl to form
tetrahedral intermediate which dissociated to produce gaseous by products hydrogen
chloride and sulphur dioxide [171].
Sample No Guar gum
(g)
Acid
Chloride
(g)
Time
(h)
DSa Yield (%)
GG-Val (136)
1.18
2.40
12
0.87
77
GG-Hex (137) 1.18 2.68 8 0.83 78
GG-Hep (138) 1.18 2.96 12 1.32 75
GG-Oct (139) 1.18 3.26 10 1.67 68
GG-Cap (141) 1.18 3.54 12 1.32 84
GG-Lau (142) 1.18 3.82 6 1.97 65
GG-Myr (143) 1.18 4.38 6 1.76 68
GG-Pal (144) 1.18 4.94 8 2.23 89
GG-Ste (145) 1.18 5.50 10 2.21 91
GG-Pel (140) 1.18 6.00 6 2.24 84
98
Table: 4.10 Elemental analysis of fatty acid chlorides synthesis via thionychloride
Sample no
Name of
Acid chloride
Elemental Analysis
C H Cl O
135a
Valeryl chloride
48.81 7.05 30.39 13.75
135b
Caproic chloride
53.54 8.34 25.24 12.88
135c
Heptanoyl Chloride
55.47 9.92 23.65 10.96
135d
Caprylic chloride
60.07 9.20 20.69 10.81
135e
Pelargonic chloride
61.20 9.68 21.07 8.05
135f
Capric chloride
61.88 11.14 18.49 8.49
135g
Lauroyl chloride
65.78 11.70 15.18 7.34
135h
Myristoyl chloride
69.10 10.06 13.29 7.55
135i
Palmitoyl chloride
69.70 11.58 10.90 7.82
135j
Stearoyl Chloride
69.80 11.48 10.80 7.92
99
4.3.2 Mechanism of Ester formation
The influence of chain length on esterification of guar gum was studies by reacting 2
mole acid chloride per mole anhydrous sugar unit of guar gum. The procedure of
Peltonen et all. described in US patent 5589577 was adopted here with slight
variations. For investigating the reaction mechanism Guar gum (GG-2) was reacted
with variety of fatty acid chlorides in the presence of accelerating agent pyridine and
reacting medium anhydrous DMF. N, N- Dimethyl formamide was proved
advantageous solvent for proposed reaction scheme [172]. After careful observation it
was observed that other solvent didn’t give required result e.g. DMSO give lower
yield and precipitation difficulties. Pyridine was used as highly reactive basic catalyst.
Reaction temperature and time varied from reaction to reaction so these conditions
were optimized for each reaction. Maximum obtainable temperature was 140 °C in
our experiments. Higher temperature shortened the reaction time [173]. Reaction
Mixture was kept under stirring until the consumption of starting material indicated
by TLC [174].
Scheme: 4.9 General reaction mechanism of the esterification of Guar gum
100
General reaction mechanism involves the nucleophilic attack of catalyst pyridine on
carbonyl carbon of acid chloride to form a complex. In next step free hydroxyl groups
of guar back bone made nucleophilic attack on the carbon of intermediate to form
corresponding ester (Scheme 4.9). Reaction could be performed without base but
reaction speed was very slow and product obtained with lower yield and substitution
degree. Pure products were obtained by precipitating in ethanol and then filtered the
reaction mixture. Reaction conditions were given in Table 4.8.
4.3.3 FTIR Spectra Analysis
The FTIR (KBr) spectra showed typical absorption for the guar gum backbone at
3630, 2940 and 1130 cm-1. A comparison of FTIR (KBr) spectrum of native gum
and guar valerate 136 prepared from a valeryl chloride 135a with a DS of 0.87
confirmed completion of reaction. Compound 136 spectra displayed hydroxyl group
stretching absorption at 3430 cm-1 which decreased in intensity which revealed the
success of reaction. The difference showed that large number of hydroxyl groups was
replaced. Increase in bond absorption at 2928-2830 cm-1 was linked with C-H bonds
antisymmetric and symmetric stretching vibrations which were another prove of
linkage of fatty long chain moieties with gum. The appearance of new bands at 1754
cm-1 and 723cm-1 corresponding to the carbonyl ester group and due to the at least
four linearly connected CH2 groups rocking vibrations. Disappearance of absorption
bands around 1330-1150 cm-1 showed that no unreacted acyl chlorides was present.
These results obtained were in good concord with the values given in literature for
cellulose and starch esters via fatty acids [175].
Similar results were obtained for other products 137- 145 irrespective of carbon chain
length as shown in table 4.11.
101
Table 4.11 Characteristic IR Absorptions of guar esters 137-145
Guar Esters
137-145
IR Vmax (cm-1)
137 3445 (OH stretch), 2938, 2825 (C-H stretch), 1754 (C=O ester),
1240(C-O-C ester), 720 (C-H rock)
138 3398 (OH stretch), 2930, 2876 (C-H stretch), 1743 (C=O ester),
1240(C-O-C ester), 722(C-H rock)
139 3470 (OH stretch), 2930, 2858(C-H stretch), 1760 (C=O ester),
1230(C-O-C ester), 722 (C-H rock)
140 3450 (OH stretch), 2930, 2950 (C-H stretch), 1740 (C=O ester),
1245(C-O-C ester), 725 (C-H rock)
141 3478 (OH stretch), 2930, 2845 (C-H stretch), 1753 (C=O ester),
1240(C-O-C ester), 727 (C-H rock)
142 3480 (OH stretch), 2976, 2845 (C-H stretch), 1743 (C=O ester),
1254(C-O-C ester), 722 (C-H rock)
143 3476(CH stretch), 2950, 2840 (C-H stretch), 1738 (C=O ester),
125o(C-O-C ester), 723 (C-H rock)
144 3476(CH stretch), 2950, 2840 (C-H stretch), 1758 (C=O ester),
1250(C-O-C ester), 725 (C-H rock)
145 3487(CH stretch), 2934, 2850 (C-H stretch), 1752 (C=O ester),
1245(C-O-C ester), 720 (C-H rock)
102
4.3.4 1H-NMR characterization of 136-145
1H NMR characterization was interesting tool to investigate the existence of the fatty
chains on the guar backbone. All the spectra showed almost similar peaks
corresponding to their fatty chain lengths. Characteristic signals due to long chain
fatty acid protons appeared between 0.79 to 2.84 ppm. All spectra showed
carbohydrate protons resonance within range of 3.35-5.78 ppm.
The 1H-NMR spectrum of 136 was recorded in DMSO showed the characteristic
signals due to sugar protons resonate at 3.8-5.6 ppm .The signals of the methylene
groups of the valearic acid appeared in the range 1.23-2.75 ppm. Methyl group
resonate at 0.97 ppm. In the same way compound 137 showed three different types of
signals at 3.8-5.6 ppm (due to sugar Protons), 1.24-2.30 ppm (CH2 group of
caproate), 0.87 ppm (CH3 group of caporate). Compound 138 showed multiple
signals at 1.35-2.33 typical for methylene protons of 138 and singlet at 0.83 due to
three protons of methyl group. The signals of the methylene groups of the compound
139, 140, 141, 142, 143 , 144 & 145 appeared in the range of 1.25-2.36, 1.26-2.82,
1.24-2.33, 1.26-2.32, 1.26-2.32, 1.26-2.34 and 1.23-2.75 respectively. All methylene
protons resonate almost at similar range irrespective of the fatty chain length. All
methyl protons of fatty acid moieties were detectable at 0.79-0.83 ppm.1H-NMR
confirmed modification of GG-2 into value added products.
103
4.4 Determination of degree of substitution of Guar Gum
derivatives
Average number of substituted hydroxyl groups per sugar unit of guar molecule
determined its degree of substitution. Maximum theoretical degree is three. Most
reliable, fast and economical method for determination of guar gum esters are via
titration methods. Different Methods are cited in literature for determination of variety
of polysaccharides derivatives. Mostly acid base back titration was done which
involved alkaline hydrolysis of substituted group (ester linkage) and titration of
excess alkali. Wurzberg method was employed here for determination of substitution
ratio of samples 126-133.Heinze, Philipp, Klemm and Wagenknecht mehod was used
for determination of DS of compounds 136-145.
Back Titration methods discussed above give more accurate, reliable and fast
determination of substitution degree. We can quantitatively measured no of hydroxyl
groups substituted per sugar unit of gum. Back titration was employed in 1947 for
determine DS values of carboxymethyl cellulose. Later on it become vastly studies
method for determination of DS of other polysaccharides.
Modified samples were treated with acid (HCl or H2SO4) to done acid hydrolysis of
substituted groups, after that they were converted into sodium, potassium salts by
treating with known amount of alkali. Back titration of excess base was done to
quantitatively determine the amount of liberated groups. Other methods could be
employed for determination of substitution of hydroxyl groups, they included H-
NMR, IR, elemental analyses etc but titration methods were` considered more simple
and accurate.
104
4.5 SECTION IV
Testing of Guar Gum Derivative
4.5.1 Surface Morphological studies of guar gum derivatives
A Surface morphological study was done with the help of scanning electron
microscopy. High and Partial Vacuum (10-10-4 Pa) Jeol- JSM5600 LV Scanning
electron microscopy with secondary electron detector at voltage between 1-30kV was
used for surface morphological studies of polymers. SEM photomicrographs of
autochthonic gum and modified gum showed remarkable difference in structure and
morphology, which was an evidence of variation in gum structure. Significant
changes in shape and size of native gum and derivatives indicated modification in
guar backbone. The appearance of native guar was portrayed under SEM with
distinctive granules, with various shapes,
Figure 4.2 SEM photomicrographs of native guar gum
105
Figure.4.3 SEM micrographs of Native Guar and Guar Esters (120-124)
106
Some have spherical, and some have cubical shapes with irregular geometry, but
intact and even surfaces. Most guar granules possessed elliptical shape with few
spherical one with a large range of granules size range from 8.7 to 30.2 .m. SEM
microspheres of guar were non-porous and having uniform solidification [176] as
expected (Figure 4.2).
Derivatization bring remarkable changes in guar derivatives 120-124 they showed
porous structure with networking which enhanced as degree of substitution increased
as shown in Figure 4.3 Particles lose their crystanility and smoothness on
modification. GGHc showed maximum networking and deformation due to greater
degree of substitution of 2.34.
Microwave modified compounds 126-133 showed no noticeable changes in
microspheres structures under SEM. It could be concluded that derivatization by
microwave irradiatin didn,t bring any remarkable changes in surface of guar
molecules. They remained intact and smooth. Very few molecules showed surface
morphological changes (Figure 4.4) so it appeared that microwaves bring no
considerable variations in microstructure of gums esters as compared to conventional
heating [177].
GGSu-129 GGMal-130
Figure 4.4 SEM images of Microwave induced derivatives
107
Guar granules lacked their individuality and smoothness for derivatives 136-145 when
observed under scanning electron microscopy. They showed transition from granules
to agglomerates upon gelatinization. There was profound increment in networking
were observed as DS value increased, because more hydroxyl groups were substituted
by fatty acids groups. Compound 144 and 145 showed maximum deformation in
structure (Figure 4.5). No considerable changes occured in morphology of compound
136.
Figure 4.5: Agglomerate morphology of Compound 145 & 146
That was evident that structure and morphology of guar derivatives changed upon
modification and GG loosed granular morphology and transit to fibriller and
agglomerate morphology.
4.5.2 Solubilities Determination of Modified Compounds
Guar gum may be recognized from other plants gums due to perfect cold water
solubility even at very low concentration. It forms highly viscous solution which
appeared as gel like complex. Water solubility of galactomannans depends upon their
108
mannose to galactose ratio. Greater is α-1-6 - D –glucopyranosyl units greater is cold
water solubility or vice versa [178].
Table 4.12 Solubility Data of guar Derivatives
Sample
No PY DMFA DMSO CHCl3 ACN DIO EtOH H2O
120 - - - - - +* - +
121 + + + + - +* +* +
122 +* +* + + - +* - +
123 - - - - - - - +
124 + + + + - + + +
126 + + + + - + + +
127 - + + - - - +* +
128 - + + - - - +* +
129 - - - - - - - -
130 - - - - - - - -
131 - - - - - - - -
132 - +* +* - - - - +*
133 - +* +* - - - - +*
136 - - - - - - - +*
137 - - - - - - - +
138 - - +* - - - - +
139 - +* +* - - - - +
140 - +* +* - - - - +
141 - +* +* - - - - +
142 - +* +* +* - - - +
143 - + + + + + + +*
144 - + + + + + + +*
145 - + + + + + + +*
+ = Soluble, - =Insoluble, +* soluble on heating
109
It seemed that the galactose groups hold back solid -state packing of mannanose
backbone and play an important role in the solution state by free rotation about the
(1→6) linkage due to conformational entropy. Due to these factors guar was not
organo-soluble which limits its applications. To enhanced and diversify its
applications different methods were employed to increase solubility of guar
derivatives in different organic solvents. The introduction of different functional
groups on gum backbone might alter its solubility profile, but it depends upon
substitution extent, substituted group nature, Temperature, type of solvent, molecular
weight etc. Mostly guar derivatives with DS value greater than 2 showed remarkable
solubilities in organic solvents. Guar derivatives commercially available with DS
lower than 1 is not soluble in typical solvents [179]. Product 120 showed solubility in
dioxane upon heating it was insoluble in all other solvents its might be due to low DS
value of 0.35. products 121 and 124 have soluble in all solvents except in acetonitrile.
Product 122 exhibited solubility on heating. Product 126 had degree of substitution
higher than 2 so it has profound effect on its solubility, its soluble in all solvent .127
&128 soluble on heating .compounds 129-130 showed no solubility in any solvent
due to smaller value of substitution.131 and 132 have soluble in DMF and DMSO
only on heating. Compounds 144-146 exhibited solubility in all solvents but they are
partially soluble in water or soluble on heating above room temperature. Other
derivatives have mixed solubility profile as shown in table 4.12.
4.5.3 Determination of Water Holding Capacity and gelation properties of guar
gum derivatives
Water-holding capacity (WHC) is an important factor which determines industrial
applications of polysaccharides. Swelling ratios or water holding capacity is ability of
hydrogels to hold water after the equilibrium attained under certain conditions
resulting in gel formation and lose of granular morphology. Due to hydrophilic nature
of GG it showed greater water uptake capacity as compared to other galactomannan
and as a result can be used to improve texture of end products in different industrial
formulations. It is prerequisite to determine swelling index of guar derivatives in the
view point of its potential applications in food, pharmaceutical, cosmetics and many
110
other commercial and industrial sectors [180]. Swelling power formulated a better
product throughout processing and enhanced end use performance.
Water holding capacity of products depends upon gum origin, microstructure,
chemical composition, isolation techniques, purity, concentration, temperature and pH
of medium etc. Variation in swelling ratios among modified samples should be
attributed to the type of functional group substituted. Relationship between swelling
of GG and molecular structure is complex phenomenon. Different literature
articulated different effects depend upon experimental conditions [181].
Table 4.13 Swelling Index of modified guar gum samples
Sample Swelling Index (%)
GG-1 26.15±2
GG-2 23.15±3
120 25.17±1
121 23.11±2
122 22.23±2
123 24.54±2
124 19.35±1.8
126 21.25±1.3
127 22.18±1.3
128 23.15±3.5
129 17.15±2.5
130 13.15±2.3
131 12.15±1.4
132 6.45 ±2.14
133 13.15±3.4
136 22.15±2.7
137 20.25±1.3
138 20.15±2.3
139 21.15±3.5
140 20.15±2.5
141 19.15±2.3
111
The degree of swelling was calculated in terms of percentage weight gain by the
samples. The swelling percentage of all the samples was investigated and given in
table 4.13.
Figure 4.6A
26.15 25.1723.11 22.23
24.54
19.35
GG‐1 120 121 122 123 124
Swelling Index of 120-124
142 14.15±1.4
143 18.45 ±2.1
144 9.18±2.33
145 6.15±2.34
146 7.43±2.4
112
Figure 4.6B
Figure 4.4C
Figure 4.6 Comparison of water holding capacity of guar gum derivatives
synthesised by different routes
23.1521.25 22.16
23.15
17.15
13.212.15
6.42
13.15
GG‐2 126 127 128 129 130 131 132 133
Swelling Index of 126-133
23.1522.15
20.25 19.8421.15
20.1519.15
14.15
18.45
9.18
6.157.43
GG‐2 136 137 138 139 140 141 142 143 144 145 146
Swelling Index of 136-145
113
The water holding capacity of samples 120-124 was not reduced significantly rather
than that of the GG-1. Percentage of Swelling ratio for sample 126-133 have been
studied carefully there was great variation in water holding capacity of these
hydrogels shown in table 4.12. Compound 136-145 showed gradual decrease in water
retention capacity. That means, gum with higher number of carbon atoms fatty chain
showed lower SI. Sample 144 and 145 were not found to have good water holding
ability due to long fatty acid chain. Fatty acids introduced hydrophobicity in guar
backbone as a result decrease in swelling ability [182-185].
Table 4.14 Gelation properties of modified guar gum samples
Sample LGC Gelation Properties
GG-1 5 V Strong gel
GG-2 6 V strong gel
120 9 Strong gel
121 7 Strong gel
122 10 Gel
123 12 Liquid
124 8 Strong gel
126 12 Liquid
127 9 Strong gel
128 8 Strong gel
129 7 V strong gel
130 10 Gel
131 11 Gel
132 10 Gel
133 12 Liquid
136 9 Strong gel
137 8 Strong gel
114
Gelation properties of autochthonic guar and its derivatives were studied. Gelation
index was determined from least gelation concentration (LGC). After modification of
gum there was reduction in gelation properties due to substitution of hydroxyl groups
by different functional moieties which hamper intergranular association between guar
molecules [186-188]. Formation of gels depends upon intermolecular forces stronger
the forces were better was swelling and hydration rates, which in turn appeared as
stronger gels. Subsitution limited the formation of stronger gels thus resulting in
weaker gels formation. Lowest LGC was obserbved for GG-1 samples, which
attributed to high molecular weight [189] and rigid and crystalline structure of guar
gum. Maximum LGC index was observed for samples 144-146 due to introduction of
hydrophobicity in guar backbone by induction of fatty acids groups. They caused
intergranular repulsion, which decrease its gelation ability. Results of gelation
properties were summarized in table 4.14. Minimum LGC value was 5 observed for
GG-1 and maximum value was 15 for compound 146. Remarkable change in physical
properties of modified GG-1 and GG-2 was observed which can improved its
applications as a binder, water barrier, and emulsifier etc in score of industrial sectors
[190].
138 9 Strong gel
139 10 Gel
140 12 Gel
141 11 Gel
142 10 Gel
143 12 Liquid
144 14 Liquid
145 13 Liquid
146 15 Liquid
115
CONCLUSION
Synthesis and characterization of guar gum esters with different synthesis paths,
analysis strategies and correlation of these structural features were studied which
provide a dominant route towards gum utilization in polymer based materials.
Alternative paths for the synthesis of guar derivatives were studied by varying
reactive intermediates and reaction conditions. A number of different reaction paths
were used to completely functionalize guar backbone using different reactants and
conditions.
In situ activation of guar gum and phenolic acids was done with
dicyclohexylcarbodiimide (DCC) and N, N-dimethylaminopyridine (DMAP) to
impart antioxidant properties to this natural gum. it was observed that efficiency of
reaction is increased by increasing temperature and reactant concentration. At room
temperature no esterification was observed for 72h probably it could be justified that
at high temperature collision between reactant increased to form a reactive
intermediate. Reaction was carried out as “one pot reaction” under homogeneous
condition using DMSO as a solvent.
The mild and elegant method for esterification of guar was carried out using different
acid anhydride with different substructures, i.e. acetic, acetate, butyrate propionate,
maleate, succinate, phthalate, citraconate and glutarate etc .This microwave induced
synthetic methodology was easily applicable for synthesis of pure aliphatic, alicyclic,
bulky and unsaturated carboxylic acid esters of cellulose with DS of 2.64 for guar
acetate using iodine as a catalyst. This mild method showed negligible degradation of
guar backbone under scanning electron microscopy. Products were soluble in organic
solvents, e.g. DMSO or DMF. DS has been determined by means of titration
Novel products with special ester functionality of long chain fatty acid were
synthesised by acid chloride route. Reactivity and selectivity of each product were
studied for different long chain carboxylic acids (C5-C18). Effect of added base
Pyridine was studied in details. Without additional base reaction reactivity was very
116
slow. It was verified that by changing reactions parameters i.e. temperature, reactants
ratio, time interval, substitution value can be controlled. Another important finding
was highest achievable DS of 2.24 within 6 hours for Guar Palmitate. Which indicate
higher efficiency of Palmitoyl chloride. Reactions efficiency increased as chain length
of acid increased. The esters synthesised were soluble in usual organic solvents
depending upon DS. The reactions proceeded with high yields. By changing the molar
ratio of the reactants, one can control DS. The guar esters prepared were highly pure
and showed no impurities.
Structure investigation of modified Guar was done by 1-H NMR spectroscopy which
has limitation due to high molecular weight and polymeric nature of complex polymer
guar. This drawback was tried to overcome by in situ hydrolysis of samples with DCl
during NMR experiments. Such first sight information can be supplemented with the
help of FTIR spectroscopy; the presence of carbonyl signal confirmed the formation
of guar esters. Moreover this technique provides more information about type of
bounded groups. Further structural elucidation was done with the help of scanning
electron microscopy (SEM) which showed deformation and enhanced networking in
synthesised compounds. The esters synthesised were characterized in detail with
regard to the DS, solubility, and swelling ratio, gelation ability using titration, FTIR,
NMR, SEM and EA techniques. Changing the molar ratios of reactants could control
DS value for each compound.
Knowledge about these structural changes can be of importance for understanding the
changed properties of guar esters. Even at products with lower DS values showed
marked difference in physical properties as compared to native one. A saturation limit
of swelling properties was observed with increasing DS value of esters. The tendency
may be investigated by studying other properties such as Viscosity, rheology, thermal
stability etc. More studied are required to discover optimal reaction conditions that
endorsed higher conversion rate, higher yield and degree of substitution.
117
Guar gum
118
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ANNEXURES
136
Annexure 1
List of Publications from this thesis
I- Iqbal, D. N., & Hussain, E. A. Physiochemical and Pharmaceutical
Properties of Guar Gum Derivatives, Asian Journal of Chemistry. 22:
7446-7452(2010).
II- Iqbal, D. N., & Hussain, E. A. Green biopolymer guar gum and its
derivatives, Int J Pharm Bio Sci. 4:423-435(2013).
III- Iqbal, D. N., & Hussain, E. A, Naz, N. synthesis and characterization of
guar gum derivatives with antioxidant moieties, (2013) (submitted).
Paper Presented in Conference from this thesis
I. Iqbal, D. N., & Hussain, E. A. synthesis and characterization of guar
acetate. Paper presented in Two days international seminar on New Trends
in chemistry, 14-15 January 2010.
137
ANNEXURE-II
