Solid acids: Green alternatives for acid catalysis

C

R

S

PD

a

ARRAA

KGSSS

C

h0

ARTICLE IN PRESSG ModelATTOD-9037; No. of Pages 18

Catalysis Today xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

Catalysis Today

j our na l ho me page: www.elsev ier .com/ locate /ca t tod

eview

olid acids: Green alternatives for acid catalysis

rincy Gupta ∗, Satya Paulepartment of Chemistry, University of Jammu, Jammu 180 006, India

r t i c l e i n f o

rticle history:eceived 29 September 2013eceived in revised form 14 April 2014ccepted 19 April 2014

a b s t r a c t

This review deals with the general discussion on green chemistry and catalysis; and solid acid cata-lysts. Various Lewis and Brønsted solid acid catalysts reported in the last few years for various syntheticprotocols have been discussed in this review.

© 2014 Elsevier B.V. All rights reserved.
vailable online xxx
eywords:reen chemistryolid acid catalystsolid Lewis acids
olid Brønsted acids
ontents

1. Green chemistry and catalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 002. Solid acid catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003. Types of solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.1. Silica based solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.1.1. Silica supported aluminium chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.1.2. Silica supported boron trifluoride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.1.3. Silica supported zinc salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.1.4. Silica supported perchloric acid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.1.5. Silica supported sulfuric acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.1.6. Silica supported sulfonic acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.1.7. Silica supported heteropolyacids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.1.8. Silica supported ionic liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.2. Zeolite based solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.3. Polymer based solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.3.1. Linear and cross-linked polymer based solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.3.2. Biopolymer based solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.3.3. Ion-exchange resin based solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.4. Hydroxyapatite based solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.5. Zirconia based solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 003.6. Carbon based solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

4. Evaluation of acidity of solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 005. Future prospects of solid acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 006. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Please cite this article in press as: P. Gupta, S. Paul, Solid acidhttp://dx.doi.org/10.1016/j.cattod.2014.04.010

∗ Corresponding author.E-mail address: [email protected] (P. Gupta).

ttp://dx.doi.org/10.1016/j.cattod.2014.04.010920-5861/© 2014 Elsevier B.V. All rights reserved.

1. Green chemistry and catalysis

s: Green alternatives for acid catalysis, Catal. Today (2014),

It is widely acknowledged that there is a growing need for moreenvironmentally acceptable processes in the chemical industry.This trend towards what has become known as ‘Green Chemistry’

dx.doi.org/10.1016/j.cattod.2014.04.010


http://www.sciencedirect.com/science/journal/09205861

http://www.elsevier.com/locate/cattod

mailto:[email protected]


IN PRESSG ModelC

2 sis Today xxx (2014) xxx–xxx

[fois[w[dtewsOi

oaafotatmedTa

eAuaowaiaLhpsTbpitw

•

••••

2

pss

•

SiO

OSi Si

OO

OSi

OOHM

X XLewis site

Brønst ed site

δ+

ARTICLEATTOD-9037; No. of Pages 18

P. Gupta, S. Paul / Cataly

1–9] or ‘Sustainable Technology’ [10] necessitates a paradigm shiftrom traditional concepts of process efficiency that focus largelyn chemical yield to one that assigns economic value to eliminat-ng waste at source and avoiding the use of toxic and/or hazardousubstances. The term ‘Green Chemistry’ was coined by Prof. Anastas3] of the US Environmental Protection Agency (EPA). A reasonableorking definition of Green chemistry can be formulated as follows

11]: Green Chemistry or environmentally benign chemistry is theesign of chemical products and processes that reduce or eliminatehe use and generation of hazardous substances. Green chemistryfficiently utilizes (preferably renewable) raw materials, eliminatesaste and avoids the use of toxic and/or hazardous reagents and

olvents in the manufacture and application of chemical products.ne of the ways of implementing the principles of Green Chemistry

s to use Catalysis.Catalysis has played a significant role in reducing pollution in

ur environment. With catalysis, reactions can be more efficientnd selective thereby eliminating large amounts of by-productsnd other waste compounds [8]. Catalysis is of crucial importanceor the chemical industry and is used to make an enormous rangef products like heavy commodity and fine chemicals. It is one ofhe fundamental pillars of Green Chemistry [12] and is considereds the most preferred and relevant technology to achieve a reduc-ion in wastes from chemical processes by use of cleaner synthetic

ethods. Catalysts accelerate reactions by orders of magnitude,nabling them to be carried out under the most favourable thermo-ynamic regime, and at much lower temperatures and pressures.hus, catalysts are the key factors in reducing both the investmentnd operation costs of a chemical process.

Acid catalysis is by far the most important area of catalysismployed by industries in all sectors of chemical manufacturing.

wide range of liquid phase industrial reactions depend on these of inorganic or mineral acids, while many of these processesre catalytic, some require (e.g. acylation using anhyd. AlCl3) sti-chiometric amounts of acids. Some of the major reaction typeshich are important in this context are Friedel–Crafts alkylations,

cylations and sulfonylations, aromatic halogenations, nitrations,somerisations, and oligomerisations. These reactions are gener-lly catalyzed by mineral acids such as H2SO4 and HF; and byewis acids such as AlCl3 and BF3. These reagents are hazardous inandling, damaging the plant through their corrosiveness and addrocess difficulties through the use of quenching and separationtages, which led to large volume of toxic and corrosive wastes.hese acids such as H2SO4, HF, AlCl3 and BF3 are typically solu-le in the organic reaction medium or remain as a separate liquidhase. At the end of the reaction, such acids are normally destroyed

n water quenching stage and require subsequent neutralization;hus, consuming additional (alkaline) resources and producing saltaste. So, in mineral acids,

volumes of process waste are commonly several times larger thanproduct volumes;waste disposal costs exceed the cost of the raw materials;are highly toxic;leads to separation problems;are environmentally undesirable.

. Solid acid catalysts

Solid acid catalysts are applicable to a plethora of acid-promotedrocesses in organic synthesis [13–15]. They have served and are


erving as an important materials due to their various advantagesuch as:

separation of the products from the reaction medium is easy;

Fig. 1. Brønsted acidity from inductive effect of Lewis acid centre coordinated to asilica support.

• catalyst can be separated easily and re-used several times withoutloss of activity;

• reactions are generally clean and products are obtained in highpurity;

• reactions are generally selective.

Solid acids can be described in terms of their Brønsted/Lewisacidity, the strength and number of these sites, and the morphol-ogy of the support (typically in terms of surface area and porosity).High product selectivity can depend on the fine-tuning of theseproperties. For example, acetal formation and hydrolysis reactionsgenerally require medium acid strength sites, while electrophilicadditions of alcohols or water to olefins, skeletal rearrangements,esterification, and alkylation reactions require strong acid sites.Likewise, the importance of the nature of the acid site is demon-strated in Friedel–Crafts alkylation reactions, where Lewis acidsites are required for alkylation of toluene using benzyl chloride,while Brønsted sites are preferred for reactions using benzyl alcohol[16]. The synthesis of pure Brønsted and pure Lewis acid catalystsattracts a great degree of academic interest, although the latter isharder to achieve because Brønsted acidity often arises from Lewisacid-base complexation (Fig. 1).

It has been shown that the type of support material used is acritical factor in the performance of the resulting supported catalystor reagent in an organic reaction system [17a]. The main factors thatshould be considered when employing a material as a support are:

• thermal and chemical stability during the reaction process andfor batch reactions during the separation stage;

• accessibility and good dispersion of the active sites.

There are numerous inorganic supports which can be used forsupporting reagents such as zeolites, silicas, polymers, hydroxyap-atite, zirconia, carbons etc. All of these materials have high surfacearea (100–1000 m2/g) and are normally porous with average porediameters ranging from the microporous zeolites to some macro-porous silicas [17b]. The particle size of these materials can rangefrom coarse to very fine. However, the choice of support materialfor the preparation of supported reagents can be the more difficultstep [17c].

3. Types of solid acids

3.1. Silica based solid acids

The chemical compound silicon dioxide, also known as silica orsilox (from the Latin word “silex”), is the oxide of silicon, chemicalformula SiO2, and has been known for its hardness since the 9thcentury. Silica is most commonly found in nature as sand or quartz,as well as in the cell walls of diatoms. It is a principal component ofmost types of glass and substances such as concrete and is usually


preferred as a supporting reagent since it is:

• widely available and inexpensive;• mesoporous and normally possess broad pore size distribution;


ARTICLE IN PRESSG ModelCATTOD-9037; No. of Pages 18

P. Gupta, S. Paul / Catalysis Today xxx (2014) xxx–xxx 3

AlClCl

O

O

OSi Si

OSi

O

OSi

Oδ+H

AlClCl

Cl

O

OSi Si

OSi

O

OSi

OH OHToluene, reflux

-HCl(g)

Fig. 2. Generation of Brønsted acid sites.

+

COCl

R

+ AlCl3 Solv ent

OAlCl3

R

Scheme 1.

Si

OH

OO

AlCl3 HCl+O

Si

O

OO

O

AlCl2

•

3

sivbpWrlaGerls

csv[s

rp

er

+

Silic a sup porte d AlCl360 oC, 4 h

Silica suppo rted Al Cl3

60 oC, 2 h

NH OMe

O N OM e

O

PhNH2OMe

O+ Ph

HN OM e

O

Scheme 3.

SiOO

SiO

OSiOH

OO

BFFF

O

O

OH R

H

+-

alkylated products, which usually observed with unsupported BF3(Scheme 4). Ether rearrangement is thought to require coordi-nation of the ether to an available Lewis acid site, which in the

Fig. 3. Generation of surface bound Lewis acid sites.

surface is heavily hydroxylated and easily functionalized.

.1.1. Silica supported aluminium chlorideAluminium chloride is the most widely used Lewis acid which is

oluble in many organic solvents and is inexpensive. Unfortunately,t is often too powerful an acid, giving unwanted side reactions, andery significantly in the context of Green Chemistry, it may need toe used in reagent quantities because of its ability to strongly com-lex Lewis base products, e.g. in a benzoylation reaction (Scheme 1).hen the reaction is complete, the only viable method for sepa-

ating the aluminium chloride is by a destructive water quench,eading to large volumes of hazardous waste. Thus, the use ofluminium chloride can lead to violations of several principles ofreen Chemistry like the release of hazardous substances into thenvironment; the use of volatile organic solvents; and the use ofeagent-like quantities that are lost on work-up; as well as unse-ective reactions that do not lead to the maximum incorporation oftarting materials in the product.

There have been several attempts to immobilize aluminiumhloride so as to overcome these problems. It has been found thatlow reaction of AlCl3 with the surface of silica in an aromatic sol-ent leads to a material with strong Brønsted and Lewis acidity18] presumably arising from the formation of SiOAlCl2 sites on theurface (Figs. 2 and 3).

Silica supported aluminium phthalocyanine complex has beeneported as a heterogeneous catalyst for the synthesis of �-aminohosphonates [19] (Scheme 2).


Silica supported aluminium chloride was found to be a highlyfficient catalyst for the Michael addition of amines to �,� unsatu-ated esters [20] (Scheme 3).

(EtO)2P(O) H, tP cAlC l

(Et O)2P(O)H, tPc AlClR1 R2

OR3NH2+ R3

HN

R1 R2OEt

OEtPO

R1

R2

NR3

Scheme 2.

Fig. 4. Hypothetical structure of the active sites in silica-supported boron-trifluoride.

3.1.2. Silica supported boron trifluorideBoron-trifluoride is widely used as a Lewis acid in industrial pro-

cesses. It is less active than AlCl3 but has the advantages of beingmore tolerant of air exposure. Silica supported BF3 is a bench-topreagent which is easy to handle providing better accessibility ofthe reactants to the active sites [21]. Direct reaction of BF3 withthe surface of silica to form Si-OBF2 units is likely to give a ratherunreactive material as a result of the strong B-O bond. This prob-lem has been removed by seeking an alternative method of surfaceattachment via complexation of the intact BF3 molecule to a surfaceoxygen with the released proton forming a conjugate cation witha suitable Lewis base e.g. alcohols can be used as a suitable base(Fig. 4). These solid acids will have limited thermal stability (limitedby the volatility of the alcohol) but are useful catalysts for a range oforganic reactions, including esterifications, Claisen–Schmidt con-densations, and phenol alkylations [13–15,21].

Silica-supported BF3 is a mild solid acid. In the alkylation ofphenols, one advantage of using this solid acid is that etherscan be C-alkylated without the rearrangement to give poly ring-


Silica-B F3

ROH

+

OR

R1CH=CH2

OR

CH2CH2R1

OR

CH2CH2R1RPoly rin g-al kylated ethers

C-alky lated ethers

BF3

Scheme 4.



4 P. Gupta, S. Paul / Catalysis Today xxx (2014) xxx–xxx

SiO

OSi

OO

SiOO

SbOSb

F FF

Fig. 5. Supported antimony trifluoride showing the effect of fluorine bridgingbetween neighbouring sites.

R1 Cl

O

R2 CH R1

R2

OZnBr2/SiO2

Neat, DIPEA+

Scheme 5.

+ CH3CN, 80 oCSiO2-ZnCl2 O

R

NH

N

O

X

H

O

O

OR

HOH2N

H2NX

cfaisC

haccf

3

fsbceiabs

eu

att

SiO2 OSnCl4-n

+CH3CN, r.t.ROH HMDS ROSiMe3 + NH3

ing out N-tert-butoxycarbonylation of amines using HClO -SiO .

H

Scheme 6.

ase of heterogeneous system, is apparently impossible. The dif-erence between the homogeneous and the supported BF3 may bettributed to steric restrictions and/or relatively weak Lewis acid-ty of the supported system [21]. Sadeghi and co-workers reportedilica supported boron-trifluoride as a stereoselective catalyst forlaisen–Schmidt condensation [22].

In addition to BF3, other supported fluorides also proved to beighly efficient Lewis acids. Antimony trifluoride is a milder Lewiscid that is capable of reacting with a hydroxylated surface to formovalent bonds. It has been found that by following a similar pro-edure as for solid aluminium chloride catalysts, apparently stableorms of supported antimony trifluoride could be made (Fig. 5) [23].

.1.3. Silica supported zinc saltsZinc chloride, which is efficient and inexpensive Lewis acid, suf-

ers from disadvantage of being hygroscopic in nature. So, whenupported on any inorganic material like silica, it attains good sta-ility without loss of catalytic activity. The mixture of aluminiumhloride and zinc chloride supported on silica was found to befficient reagent system for Beckmann rearrangement [24]. Sil-ca supported zinc bromide (ZnBr2/SiO2) [25] has been introduceds an efficient heterogeneous catalyst for the synthesis of ynonesy cross-coupling of acid chlorides with terminal alkynes underolvent-free conditions at room temperature (Scheme 5).

Gupta et al. [26a] have reported silica supported ZnCl2 as anfficient catalyst for the synthesis of dihydropyrimidinones/thionessing acetonitrile at 80 ◦C (Scheme 6).

Niknam et al. [26b] prepared silica-supported tin chloride


nd titanium tetrachloride by the reaction of tin chloride anditanium tetrachloride with activated silica gel in refluxingoluene and employed them as catalysts for the synthesis of

R2

O

O

2

OHCCHO

SiO2 OMCl

Solvent-free/90

M= Sn, TiH2N

NH2

O2

+

Scheme

R = pri mary, secon daryan d tertiary alkyl a nd aryl

Scheme 8.

bisdihydropyrimidin-2(1H)-ones from aromatic dialdehydes, 1,3-dicarbonyl compounds and urea at 90 ◦C under solvent-freeconditions (Scheme 7).

Niknam and co-workers [26c] also reported the use of silica-supported tin chloride [SiO2-Sn(Cl)4−n] for the conversion ofprimary, secondary, tertiary alcohols as well as phenolic hydroxylgroups to their corresponding trimethylsilyl ethers with hexame-thyldisilazane (Scheme 8). They investigated selective silylation ofmixtures of alcohols in the presence of amine, amide, and thiol func-tionalities and found that the method was highly selective for theprimary alcohols such as benzyl alcohol and 2-phenylethanol. Theprimary alcohols were completely converted to the correspond-ing silyl ethers while tertiary alcohols were untouched. Excellentchemoselectivity was also observed for the conversion of secondaryalcohols and phenols in the presence of tertiary alcohols such as �-terpinene and1-phenyl-2-methyl- 2-propanol. They also exploredthe chemoselectivity of silica-supported Sn(Cl)4−n in the silylationmethod and it has been shown that alcohols and phenols in thepresence of an amine, amide and thiols were completely convertedto the corresponding trimethylsilyl ethers as the sole product.

3.1.4. Silica supported perchloric acidPerchloric acid impregnated onto silica gel has gained con-

siderable attention in current organic synthesis due to its easeof preparation, high efficiency, environmental benignity, reusabil-ity, economic viability and has received considerable attentionfor numerous organic transformations, including acylation ofalcohols [27] or aldehydes, [28] the Ferrier rearrangement, [29]cleavage of benzylidene acetals, [30] electrophilic substitutionof indole with various aldehydes and ketones, [31] synthesis ofHantzsch dihydropyridines, [32] homoallylic amines through athree-component reaction, [33] tetrasubstituted imidazoles undersolvent-free conditions [34], 1,8-dioxo-octahydroxanthenes viaKnoevenagel condensation [35]. In addition to the above mentionedreactions, following are some of the important reactions catalyzedby HClO4-SiO2.

Shaterian et al. [36] have described an efficient protocol for thepreparation of amidoalkyl naphthols employing a one-pot conden-sation reaction of 2-naphthol, aromatic aldehydes and acetonitrileor acetamide in the presence of silica supported perchloric acidunder solvent, solvent-free and microwave irradiation (Scheme 9).

Chakraborti et al. [37] reported an efficient method for carry-


4 2Nasr-Esfahani et al. also used this catalyst for one-pot synthesisof �-acetamido ketones [38]. Ramesh et al. [39] reported a simple,efficient and practical method for the synthesis of dihydropyridines

4-n

oC

NHHN

O

R2

O

HN NH

O

R2O

7.




HClO4-SiO2CHO

OH

OH

NHO

+X

t�

3

aalNditaIieCchsht

3

olaSaBdfaffifhaamlet

ArCHO + 2MCM-41-R-SO3H

CH3CN, reflux

O

O O

ArO O

Scheme 11.

H2O, 150 oC

Magnetic nanoparticlesOH

OHO

OH

OH

HOHO OH

OH

H3CX

Scheme 9.

hrough a one-pot three-component coupling of cinnamaldehyde,-keto ester and aromatic amines using this catalyst (Scheme 10).

.1.5. Silica supported sulfuric acidThe widespread importance of sulfuric acid and other sulfur (VI)

cids mainly methane sulfonic acid and triflic acid have encouraged substantial amount of research into their heterogeneous ana-ogues [40,41]. Silica sulfuric acid is a superior proton source thanafion-H, [42] for carrying out reactions under heterogeneous con-itions. It [43] has been used to catalyze a wide variety of reactions

ncluding aldol condensation, [44] acetalization, [45] deacetaliza-ion, [46] oxidation of alcohols, [47] N-nitrosation of secondarymines, [48] and direct etherification of trimethylsilylethers [49a].n a review by Salehi et al. the use of silica sulfuric acid and sil-ca chloride for various organic functional group transformationsither as reagent or as catalyst has been described [49b]. Recently,rude bio-oil from pine chip was upgraded with olefins (1-octene,yclohexene, 1,7-octadiene, and 2,4,4-trimethylpentene) and alco-ols (iso-butanol, t-butanol and ethanol) at 120 ◦C using silicaulfuric acid and it has been reported that good surface area andigh pore volume are the reasons for the activity of the catalyst inhe experimental conditions [50].

.1.6. Silica supported sulfonic acidsIn recent years more emphasis is made on solid acids containing

rganic–inorganic hybrids in which acid functionality is cova-ently anchored onto support material. Among various covalentlynchored solid acids, silica functionalized sulfonic acid (SiO2-O3H) [51] finds more utility in organic synthesis and behavess an organic-inorganic hybrid (interphase) catalyst, wherein therønsted acid sites have been selectively created [52]. In the lastecade, the preparation of mesoporous solid acid catalysts hasocused on the functionalization and modification of silica-basednd organosilica hybrid materials with sulfonic acid groups. Sul-onic acid functionalized mesoporous silicas are usually preparedrom the oxidation of -SH groups with H2O2 post-grafted or directlyncorporated onto the silica walls. However, the silica walls wereunctionalized only by a limited amount of –SH groups due to theydrophobic nature of the silane agents and there is a need to avoid

possible Si–C bond cleavage in the processes of direct synthesisnd surfactant removal. Accordingly, sulfonic acid functionalized


esoporous silica materials have relatively low -SO3H densities,ow activity and low hydrothermal stability in boiling water. How-ver, Jérôme et al. [53] and Fukuoka et al. [54] have developed waterolerant sulfonic acid functionalized mesoporous silicas.

Silica supported sulfuric acid

+H

ONH2

R4

R3

H3C X

O O

Scheme 1

nOH OH

Scheme 12.

Some important sulfonic acid based catalysts used in organicsynthesis are described below: Sulfonic acid-functionalizedplatelet SBA-15 materials (SA-SBA-15-p) [55] with ordered shortmesochannels (150–350 nm) and acid capacities up to 1.2 mmolH+g−1 were synthesized by one-pot co-condensation of tetraethylorthosilicate (TEOS) and 3-mercaptopropyltrimethoxysilane(MPTMS) in the presence of appropriate amounts of Zr(IV) ions andH2O2 and used as catalysts for biodiesel synthesis by esterificationof long chain carboxylic acids with methanol. The short-channelSA-SBA-15 materials showed higher catalytic activities than theconventional rod-like or fiber-like analogues due to better molecu-lar diffusion and are superior to other catalysts because of the highaccessibility of the sulfonic acid sites in the well-ordered largemesopores (ca. 7 nm) to the reactant molecules. Mahdavinia et al.[56] reported the use of sulfonic acid functionalized MCM-41 for thesynthesis of 1,8-dioxo-octahydroxanthenes [56] (Scheme 11) andNaeimi et al. [57] used sulfonic acid-functionalized magnetic Fe3O4nanoparticles (Fe3O4@-SiO2–SO3H) for the synthesis of 1,8-dioxo-octahydroxanthene derivatives under solvent free conditions.

Lai et al. [58] have prepared sulfonic acid functionalizedmagnetic SBA-15 catalyst (Fe3O4–SBA–SO3H) which is the firstmagnetic solid acid with ordered mesoporous structure and usedit for the hydrolysis of cellulose. The catalyst was prepared by theco-condensation of tetraethoxysilane (TEOS) and mercaptopropyltrimethoxysilane (MTPMS), and oxidation of mercapto groups inthe presence of magnetic Fe3O4 nanoparticles (MNPs), triblockcopolymers and hydrogen peroxide. The sulfonic acids in channelswere found to be sufficiently robust to hydrolyze 1,4-glycosidicbonds and the catalyst can be easily separated from the reactionsystem by magnetic force (Scheme 12).

The preparation of a novel high surface area Nafion resin/silicananocomposite catalyst in which Nafion particles are encapsulatedwithin a porous silica network was reported by Lim and co-workers[59]. It has been reported that the effective surface area of the resinincreased significantly as the resin particles were entrapped withinthe highly porous silica network resulting in exposure of a number


of acid sites which provides enhanced catalytic effects.Ng et al. [60] reported sulfonic acid functionalized MCM-41

catalyst for tert-butylation of hydroquinone. Liu and co-workers[61] demonstrated the use of sulfated graphene for acid-catalyzed

HCl O4-SiO2

CH3CN, R.T., 20 min

R1 N

Ph

OEt

O

R4

R3R2

R1

R2

0.




ArCHO NH COCH

OH OH

Ar NH

CH3O

MCM-41 -N-prop ylsul famic acid

Solvent -free, 130oC+ +

eme 13.

lffgcmgfudgplf

tss4n[db[p1

(ag[tbufao1q[[4nsdNs

ad(

3

cm

H2N NH2

O

Ar

O HN

N N

NH

O O

, KHSO4

CH3CN , 80 oCR

CHO

RR

+

SiO2

OOOSi

SO3-H+

2 3

Sch

iquid reactions. The sulfated graphene was synthesized from aacile hydrothermal sulfonation of reduced graphene oxide withuming sulfuric acid at 180 ◦C. It has been reported that sulfatedraphene was much more active than the conventional solid acidatalysts Amberlyst 15, OMC-SO3H, SO3H-functionalized orderedesoporous silica (SBA-15-SO3H), graphene oxide, and reduced

raphene oxide, which was attributed to the fact that the sul-ated graphene almost has no limitation of mass transfer due to itsnique sheet structure. Moreover, sulfated graphene has extraor-inary recyclability which was attributed to the stable sulfonicroups on the sulfated graphene. Hajjami and co-workers [62a]repared MCM-41-N-propylsulfamic acid by the reaction of propy-

amine functionalized MCM-41 and chlorosulfonic acid and used itor one-pot synthesis of 1-amidoalkyl-2-naphthols (Scheme 13).

Silica-bonded S-sulfonic acid (SBSSA) [62b] prepared byhe reaction of 3-mercaptopropylsilica (MPS) and chloro-ulfonic acid was employed as a recyclable catalyst for theynthesis of 1,1-diacetates, quinoxaline derivatives [62c],,4′-alkylmethylene-bis(1H-pyrazol-5-ols) [62d], �-aminoitriles [62e], coumarins [62f], trisubstituted imidazoles62g], 2,3-dihydroquinazolin-4(1H)-ones [62h], 1,8-dioxo-ecahydroacridines, 1,8-dioxo-octahydroxanthenes [62i],is-indolylmethanes [62j] and for the silylation of hydroxyl groups62k] by Niknam and co-workers. They reported silica-bondedropyl-S-sulfonic acid for the synthesis of 2-aryl-1-arylmethyl-H-1,3-benzimidazole derivatives [63].

Niknam and co-workers also reported sulfuric acid ([3-3-silicapropyl)sulfanyl]propyl)ester [64a] for the formylationnd acetylation of alcohols, for the silylation of hydroxylroups [64b] and for the synthesis of �-amino nitriles64c], 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) [64d], 1,2,4,5etrasubstituted imidazoles [64e], 2-aryl-1-arylmethyl-1H-1,3-enzimidazoles [64f] and prepared various sulfamic acids andsed them in organic syntheses. Silica-bonded N-propyl sul-amic acid (SBNPSA) [65a] was used for the formylation andcetylation of various alcohols and amines, for the preparationf different amides by Ritter reaction [65b], for the synthesis of,8-dioxo-decahydroacridines, 1,8-dioxo-octahydroxanthenes,uinoxalines [65c] and 2,3-dihydroquinazolin-4(1H)-ones65d]. Silica-bonded propylpiperazine-N-sulfamic acid (SBPPSA)65e] used for the synthesis of highly substituted imidazoles,,4′-(arylmethylene)bis(1H-pyrazol-5-ols) [65f] and �-aminoitriles [65g]. Silica-bound N-propyl triethylenetetramineulfamic acid [65h] was used for the synthesis of 2-amino-4,6-iarylnicotinonitriles. Silica-bonded propyl-diethylene-triamine--sulfamic acid [65i] was employed as a recyclable catalyst for theynthesis of 1,1-diacetates and �-amino nitriles [65j].

We have reported silica functionalized sulfonic acid cat-lyzed one-pot synthesis of 4,5,8a-triarylhexahydropyrimido[4,5-]pyrimidine-2,7(1H,3H)-diones [66] under liquid phase catalysisScheme 14).


.1.7. Silica supported heteropolyacidsA heteropolyacid is a class of acids made up of a particular

ombination of hydrogen and oxygen with certain metals and non-etals. This type of acid is frequently used as a reusable acid

H HAr

Scheme 14.

catalyst in chemical reactions. To qualify as a heteropolyacid, thecompound must contain:

• a metal such as tungsten, molybdenum or vanadium, termed theaddenda atom;

• oxygen;• an element generally from the p-block of the periodic table such

as silicon, phosphorus or arsenic termed the hetero atom;• acidic hydrogen atoms.

The metal addenda atoms linked by oxygen atoms form a clusterwith the heteroatom via oxygen atoms. Examples with more thanone type of metal addenda atom in the cluster are well known. Theconjugate anion of a heteropolyacid is known as a polyoxometalate.Due to the possibilities of there being different combinations ofaddenda atoms and different types of hetero atoms, there are alot of heteropolyacids. Two of the better known groups of theseare based on the Keggin, HnXM12O40, and Dawson, HnX2M18O62,structures. The heteropolyacids are widely used as homogeneousand heterogeneous catalysts [67], particularly those based on theKeggin structure because of their qualities such as good thermalstability, high acidity and high oxidizing ability.

Heteropolyacids (HPAs) have attracted scientific community’sattention recently due to their excellent water tolerant ability,strong Brønsted acidity (stronger than conventional homogeneousacid, H2SO4) and high catalytic activity and stability [68]. Typi-cal HPAs which are easily available are H3PW12O40, H4SiW12O40,H3PMo12O40 and H4SiMo12O40 [69]. In addition, adding appropri-ate ratio of salt (Cs+, NH4

+ and Ag+) to HPAs will dramaticallyincrease its surface area and allow easier accessibility of reac-tant to its active sites [70]. Although in general, heteropolyacidswork as homogeneous catalysts, they can be heterogenized eitherby supporting them on a high surface area carrier such as silicaor by combining with monovalent cations such as NH4

+, K+, Cs+,and Ag+ [71], e.g. Keggin heteropolyacid H3PW12O40 is soluble inmethanol and ethanol, while the ammonium salt is insoluble inalcohol and used as solid acid catalyst for hydration of isobutyleneand polymerisation of tetrahydrofuran. The major disadvantagesassociated with HPAs include low thermal stability and low surfacearea, therefore, in recent years, there has been much interest in thesynthesis, characterization and catalytic properties of HPAs, espe-cially supported ones. Surface area enhancement, higher dispersing


of acidic protons, heterogenization and acid strength control aresome of the goals for preparing supported HPAs. It is necessary topay attention to the homogeneity of dispersion because it can pro-duce changes in the acid strength, the structures of the aggregates




Catal yst

Solvent-free+ +

Ph

Ph O

CHO CH2NH2 N

NPh

Ph

Ph

Ph

O

Scheme 15.

+ Catal yst

OMeO OMe NRNH2

aicco

pcts(bwr

t2m

aane[

3

gbmiCtpncihaitboamcos

pi

R1CHOImmobiliz ed IL

Solven t-free, 85 oC+ +

Immobilized IL

OH

R2 NH2

O

NHCOR2

OH

R1

Silic

a

OO

OSi N N

SO3HHSO4

-

Scheme 17.

Catalyst

Cyclohexane H2O

Fe3O4 O SiO

OP

SO3H

SO3H

SO3HCl-

R1 R2

O OH

OH

OO

R1

R2

+ +

Me

Scheme 16.

nd the possibility of decomposition. It appears to be an interest-ng challenge to synthesize and characterize supported HPAs asatalyst in the synthesis of fine chemicals or biologically activeompounds. Heteropolyacids have been known to catalyze manyrganic transformations. Some of them are listed below:

Rafiee and co-workers [72] prepared a series of 12-hosphotungstic acid (PWA) supported on various porousarriers, such as silica, alumina, titania, clay, carbon and evaluatedheir catalytic performance for the synthesis of imidazoles underolvent-free conditions. It was found that PWA supported on silicaPWA/SiO2) showed higher activity compared to other catalystsecause specific surface area for supported samples diminishith respect to the support due to PWA incorporation and this

eduction was more pronounced for PWA/SiO2 (Scheme 15).Tungstophosphoric acid supported on silica gel was reported

o be an efficient catalyst for the synthesis of pyrroles from,5-dimethoxytetrahydrofuran in solution or under solvent-freeicrowave irradiation (Scheme 16) [73].Recently, an expedient method of silica supported heteropoly-

cid (HPA) catalyzed liquid phase dehydration of aldoxime to nitrilend secondary alcohols to alkenes has been developed [74] andano-silica supported preyssler heteropolyacid has been used forsterification of salicylic acid with aliphatic and benzylic alcohols75].

.1.8. Silica supported ionic liquidsWith the continuing depletion of natural resources and the

rowing environmental awareness, current and future chemists areeing trained to develop synthetic routes in economically beneficialanner. Among the novel green solvents that have been reported,

onic liquids (ILs) have been one of the most active areas of Greenhemistry over the past decade due to their excellent chemical andhermal properties such as good thermal stability, negligible vapourressure, ease of handling, potential for recycling, good coordi-ating and dissolving capabilities. Additionally, the physical andhemical properties of the ionic liquids can be adjusted by chang-ng the combination of the cation and the anion and so acidic, basic,ydrophilic or even hydrophobic ionic liquids can be synthesizednd used in organic synthesis. Recently, the use of immobilizedonic liquids [76–79] is an active area of research. ILs can be boundo a support surface either by covalent bonds or without covalentonds in the form of supported liquid phases (SLPs). Compared tother well-known acid catalysts, immobilized ILs have increaseddvantages such as easily tunable acidity, high surface area andore pore width and moreover, by changing the length of side-

hains of the inorganic cation, the hydrophilicity or hydrophobicityf the surface can be enhanced. Some of the reactions catalyzed by


ilica supported ionic liquids are presented below:Zhang et al. [80] reported a supported dual acidic ionic liquid

repared via anchoring 3-sulfobutyl-1-(3-propyltriethoxysilane)midazolium hydrogen sulfate onto silica and used it to catalyze

Cataly st

Scheme 18.

the synthesis of amidoalkyl naphthols by the condensation of alde-hydes with 2-naphthol and amides under solvent-free conditions(Scheme 17).

Silica supported ionic liquid nanoparticles with varied par-ticle sizes have been synthesized and successfully employedas solid acid catalysts for the dehydration of fructose to 5-hydroxymethylfurfural by Sihpuria and co-workers [81]. It has beenreported that the highest selectivity for HMF has been obtained inthe presence of DMSO as a solvent because the furanoid form is pre-ferred in DMSO. A novel magnetic nanoparticles supported dualacidic ionic liquid was synthesized by anchoring 3-sulfobutyl-1-(3-propyltriethoxysilane) imidazolium hydrogen sulfate onto thesurface of silica-coated Fe3O4 nanoparticles. Due to the combi-nation of nano-support features and flexible imidazolium linkers,it acted as a “quasi-homogeneous” catalyst to effectively catalyzethe one-pot synthesis of benzoxanthenes by a three-componentcondensation of dimedone with aldehyde and 2-naphthol undersolvent-free conditions [82]. Wang and co-workers have reportedionic liquid functionalized magnetic nano solid acid catalyst [83]for acetalization of aldehydes and ketones with ethylene glycol(Scheme 18). The catalyst was prepared by grafting an ionic liquidonto Fe3O4 nanoparticles followed by sulfonation of phenyl groupsin the ionic liquid. 1-Allylimidazolium containing acidic ionicliquids were immobilized on 3-mercaptopropyltrimethoxysilanemodified silica by Qiao et al. and used as a recyclable solid acidcatalyst for esterification of alcohol with acetic acid and nitrationof aromatic compounds with aqueous nitric acid (Scheme 19) [84].

Silica-grafted imidazolium-based ILs with carboxylic acid andhydroxyl groups and with no functional group, have been demon-strated as effective catalysts for the synthesis of cyclic carbonatesvia the cycloaddition of epoxides with CO2 (Scheme 20) and itwas found that carboxylic acid-functionalized catalysts showed thehighest activity and selectivity, since the –COOH group in the IL


cation can greatly accelerate the reactions and showed a synergis-tic effect [85] with the halide anions. Fehér et al. [86a] reportedBrønsted acidic ionic liquids supported onto silica for oligomerisa-tion of isobutene.




N N

Immobilized IL

Silic

a O

OSi

S

(CH2)nSO3X.CF3SO3

-OMe

R

HNO3Immobilized IL

+

R

NO2

H2O+

Scheme 19.

CO2

Catal ystO

R

O O

R

O

OO

CO2

CatalystO

O O

O

N NR(R')O

OSiOEt

X-Silica

(r3c

(h�abtgiu2tars

N N-

ROH + HMDS ROTMS + NH3cat.

CH3CN, r.t.

N H+

CF3COO-

a

SiO2 H+

Cl

N NSiO2 H+CF3COO-

b

c

cat. :

Cata lyst

Scheme 20.

Baghernejad et al. [86b] reported synthesis of 4,4′-Arylmethylene)bis(1H-pyrazol-5-ols) by the condensationeaction between aldehydes and 5-methyl-2-phenyl-2,4-dihydro-H-pyrazol-3-one in the presence of [Sipmim]HSO4 as solid acidatalyst (Scheme 21).

Nouri-Sefat and co-workers [86c] reported preparation of N-3-silicapropyl) imidazolium hydrogen sulfate ([Sipim]HSO4) as aeterogeneous acidic ionic liquid and used it for the synthesis of-amino nitriles by a one-pot condensation of aldehydes, amines,nd trimethylsilyl cyanide at room temperature (Scheme 22). It haseen demonstrated that Brønsted acid counter ions perform betterhan other counter ions. Ionic liquids with the HSO4

− counter ionive better results than H2PO4

− with respect to time and yield. Thiss due to the acidic power of HSO4

− over H2PO4− When -OTf was

sed as the counter ion there was no product formation even after4 h while in the case of [Sipim]OTf or [Sipmim]OTf as catalysts,


his condensation was accomplished in 180 and 110 min with 70%nd 85% yields, respectively. These results clearly demonstrate theole of counter ions in the catalytic activity of their correspondingupported and non-supported ones.

S ilic

a

OO

OSi N

ArCHO NN O

Me

Ph

2+Ethanol, re

Scheme 2

Sil ic

a

OO

OSi

Ethan15-160

R1CHO + R 2NH2 + TMSCN

Scheme 2

Scheme 23.

Tajik et al. [86d] reported silylation of alcohols and phenolsby HMDS in the presence of ionic liquid and silica-supportedcatalysts (Scheme 23). Niknam et al. [86e] also reported silica-grafted N-propyl-imidazolium hydrogen sulfate ([Sipim]HSO4) asa recyclable heterogeneous ionic liquid catalyst for the synthe-sis of 3,4-dihydropyrano[c]-chromenes and for the synthesis ofpyrano[2,3-c]-pyrazoles.

3.2. Zeolite based solid acids

Zeolites are natural or synthetic aluminium silicates which forma regular crystal lattice and release water at high temperature.The term zeolite was coined in 1756 by the Swedish mineralo-gist Cronstedt who observed that the mineral stilbite frothed andgave off steam when heated [87]. The general formula for zeolitesis xM2/nO·xAl2O3·ySiO2·zH2O, are polar in nature and often referredto as molecular sieves. They have the ability to act as catalysts forchemical reactions which take place within the internal cavitiesand have been used as catalysts in many organic reactions, includ-ing crude oil cracking, isomerisation and fuel synthesis. They canalso serve as oxidation or reduction catalysts, often after metalshave been introduced into the framework.

Underpinning all these types of reaction is the unique micro-porous nature of zeolites, where the shape and size of a particularpore system exerts a steric influence on the reaction, controlling theaccess of reactants and products. Thus, zeolites are often said to actas shape-selective catalysts. They are commonly used in catalysisfor shape selective reactions such as bromination, chlorination, acy-lation, methanesulfonylation of aromatic compounds etc. In theseliquid phase reactions, there are two principal roles of the zeolites:


i. they provide sites capable of enhancing the rate of a reaction ineither a stoichiometric or catalytic manner;

NHSO 4

-

ux

NN

OH

Me

Ph NN

Ph

Me

HO

Ar

1.

N NHHSO 4

-

ol, r.t. min

HC NHR1CN

R2

2.


IN PRESSG ModelC

sis Today xxx (2014) xxx–xxx 9

i

buAIvoiiwattssrst

mpTpfs

3

etbp

3

aluqnasPprtbPaoTa

+R1 R2

O

SH SH Dichlo roet haneS S

R1 R2

Ps-AlCl3 or Ps -FeCl3 or Si O2-AlCl3

Scheme 25.

Ps-Al(OTf)3/Ac2O

CH2Cl2/ R. T.R H

O R

H

OAc

OAc

Scheme 26.

R2OH0.2 mol% catalyst

25-95 oC+ H2O+

++4.3 mol% cata lyst

90 oC

+ 1.0 mol% catalys to

R1 OH

O

OCH3

O

O O

O

R1 OR2

O

OCH3

O

OH

O

boron trifluoride (PVPP-BF3) and used it for selective amidation ofbenzhydrol and tertiary alcohols with nitriles. In contrast to borontrifluoride which is extremely moisture sensitive, PVPP-BF3 is not



i. by having these sites located within the rigid pores of the inor-ganic matrix, they also impose additional constraints on thereacting partners, favouring production of one isomer (usuallythe most linear one) over other possible ones.

Various reactions catalyzed by zeolites are presented below:A novel catalyst was prepared by solid-state interaction

etween ZnCl2 and NaY zeolite using microwave irradiation andsed as a heterogeneous catalyst for the high regioselective Diels-lder reaction of myrcene and acrolein by Liu and co-workers [88].

t has been reported that the catalytic activity and the regioselecti-ity of p/m strongly depend on the ZnCl2 loading. With an increasef the ZnCl2 loading up to 0.92 mmol g−1, the activity and selectiv-ty increase a little and the active site was deduced from the zincon species formed by solid-state ion exchange. The Lewis acid sites

ere too weak to catalyze efficiently the Diels–Alder reaction andn increase of ZnCl2 loading from 0.92 mmol g−1 to 1.84 mmol g−1,he activity and the regioselectivity of p/m increased markedly dueo the formation of new zinc ion species of –O–Zn–Cl as Lewis acidites on NaY zeolite. Kubota et al. [89] reported MSE-type zeoliteolid acid catalyst for hexane cracking. In a recent review [90], Chicaeported the role of zeolites in the preparation of highly active andelective ethanol steam reforming catalysts and their main proper-ies to be used as efficient water splitting photocatalysts.

The hydration of �-pinene yielding a complex mixture ofonoterpenes, alcohols and hydrocarbons has been studied in the

resence of Y-zeolite (Si/Al = 2.89) by Wijayati and co-workers [91].he selectivity of �-terpineol (the monocyclic alcohol) as mainroduct was 59.20% with a conversion of 83.83% and it has beenound that the conversion and selectivity to �-terpineol increaseignificantly with increase in temperature and reaction times.

.3. Polymer based solid acids

The use of polymer [92] supported reagents represents a pow-rful approach for the synthesis of organic compounds, using bothraditional and parallel solution phase methodologies and it haseen of great interest in recent years, especially in the field ofharmaceutical sciences.

.3.1. Linear and cross-linked polymer based solid acidsIn recent years, a large number of polymer-supported Lewis

cids have been prepared by immobilization of the cata-ysts on polymers via coordination or covalent bonds and aresed in many organic transformations [93–96]. The most fre-uently used polymeric support is polystyrene; its hydrophobicature protects water-sensitive Lewis acids from hydrolysis bytmospheric moisture until it is suspended in an appropriateolvent where it can be used in a chemical reaction [95,97].olystyrene-supported aluminium chloride has emerged as aromising heterogeneous Lewis acid catalyst for acid-catalyzedeactions such as Friedel–Crafts acylation and sulfonation reac-ions; tetrahydropyranylation of alcohols and phenols; synthesis ofis-indolylmethanes [93a,93b,98] and N-substituted pyrroles [99].olystyrene supported aluminium chloride has also been reported


s an efficient and recyclable green catalyst for one-pot synthesisf 14-aryl or alkyl-14H-dibenzo[a,j]xanthenes [100] (Scheme 24).his immobilized aluminium chloride catalyst is not sensitive toir and moisture upon storage and much easier to handle than its

+Polysty rene/Al Cl3

CH3CN, refl ux2H2O+

O

ROH

RCHO

Scheme 24.

50 CO O O

Scheme 27.

soluble counterpart, AlCl3. Wang et al. [101] prepared an immobi-lized Lewis acid catalyst CPVA-AlCl3 where cross-linked polyvinylalcohol (CPVA) was used as a support and evaluated its catalyticactivity in Friedel–Crafts acylation reaction of polystyrene in CCl4.

Tamami et al. [102] reported cross-linked polystyrene sup-ported AlCl3 and FeCl3 as a mild and chemoselective heterogeneouscatalysts for the dithioacetalization of carbonyl compounds(Scheme 25). The efficiency of the catalyst was attributed to itsstrong affinity for carbonyl oxygen faciliating the formation of theintermediate hemithioacetal and the hydrophobic nature of thepolystyrene.

Polystyrene supported Al(OTf)3 has been used for the chemos-elective synthesis of acylals from aldehydes [103] (Scheme 26).The observed high chemoselectivity of acetylation reactions wasa result of mild catalytic activity of Ps-Al(OTf)3, difference in stericbulkiness of the carbonyl compounds and also the influence of elec-tronic effects upon these reactions in the presence of Ps-Al(OTf)3.

Granados et al. [104] reported the catalytic activity ofpoly(styrenesulfonic) acid (PSSA) in three different reactions drivenby acidic sites: tributyrin methanolysis, biodiesel synthesis andxylose dehydration to furfural. Okayasu described the use of apoly(vinylsulfonic acid) (PVS)-grafted polystyrene for esterifica-tion, Friedel–Crafts acylation and condensation reactions [105](Scheme 27).

Sugimura et al. [106] reported 1-vinylimidazolium based ionicliquids supported on styrene as a heterogeneous catalyst for acetalformation (Scheme 28).

Lakouraj [107] introduced polyvinylpolypyrrolidone-supported


Scheme 28.




' PVPP-BF3

h(

mmrwac

ch[vfscaTa

Mmaaticma

3

ctwahe[dpHmT0nacoobtc

3

apis

RCHO R1R2NHNafion®NR50, CH3CN

70-8 0 oC, N2 atm+ +

N

R

R1R2
+ROH R CN RNHCOR'
Scheme 29.

ygroscopic and retains its activity after several months of storageScheme 29).

Lanthanide triflates have received considerable attention asild, water-stable Lewis acids in a wide range of organic transfor-ations [108]. Polymer-supported lanthanide triflates have been

eported by Koyabashi and Janda’s group [94a,94b,109]. Comparedith lanthanide triflates, bismuth triflate is less expensive, remark-

bly non-toxic and easily prepared even on a multi-gram scale fromommercially available bismuth oxide and triflic acid [96a].

Lee et al. developed cross-linked poly(4-vinylpyridine/styrene)opolymer-supported ytterbium(III) triflate as an efficienteterogeneous catalyst for the synthesis of �-amino ketones110] and recently, they have also reported [111] poly(4-inylpyridine/styrene) copolymer-supported bismuth(III)triflateor the trimethylsilylation of alcohols and phenols. A polymer-upported gadolinium triflate [96c] was prepared fromhloromethyl polystyrene (CMPS) resin and was used for thecetylation of various alcohols and phenols with acetic anhydride.he swelling property of crosslinked resin in organic solvents wasn important factor for these solid-phase reactions.

A new hierarchical macro/mesoporous titanium phosphateTiP-1 [112] has been synthesized through a slow evaporationethod by using titanium isopropoxide and orthophosphoric acid

s inorganic sources and pluronic P123 as the structure directinggent. This MTiP-1 material shows very good catalytic activity inhe microwave assisted conversion of biomass and carbohydratesnto 5-hydroxymethylfurfural (HMF). The macroporous hierarchi-al porosity of the catalyst gives better access to the internalesoporosity improving mass transport throughout the material

nd thus helps to improve the catalytic activity.

.3.2. Biopolymer based solid acidsIn recent times, natural biopolymers have emerged as potential

andidates for preparing solid acid catalysts and cellulose is one ofhe most abundant natural biopolymers in the world that has beenidely studied during the past decades because it is a biodegrad-

ble material and a renewable resource. Cellulose sulfonic acidas emerged as a promising catalyst for acid catalyzed reactions,.g. in the synthesis of �-amino nitriles, [113] imidazoazines,114] xanthenes, [115] quinolines, [116] C5-unsubstituted 1,4-ihydropyridines, [117] quinazolin-4(1H)-ones, [118] substitutedyrroles [119a] and for the protection of hydroxyl groups usingMDS [119b]. Its catalytic properties are attributed to its high ther-al stability and strong acid sites of sulfonic acid functional groups.

he number of acidic (H+) sites in the cellulose sulfuric acid is.50 meq g−1 in the basis of acid-base titration [119c]. Recently, aovel solid acid catalyst was prepared from sodium alginate (SA)nd metal chlorides [120] and was found to be a good candidate foratalytic conversion of cheap feedstocks containing high amountf FFAs (such as inedible oils, waste vegetable oils, waste cookingils, etc.) into biodiesel. It has been reported that the ferric-alginateeads can withstand the refluxing temperature without degrada-ion and showed the formation of FeOOH that held the alginatehain in place.

.3.3. Ion-exchange resin based solid acidsIon-exchange resins are insoluble macroporous polymers which


re capable of exchanging specific ions with other ions within theolymer itself in a solution or reaction media. Normally, sulfonic

on-exchange resins are co-polymers of divinylbenzene (DVB),tyrene and sulfonic acid groups (as the active sites-Brønsted

Scheme 30.

acidity) [121]. The polymer structure of the resin is mainly charac-terized by the composition of cross-linking component (normallyDVB) which will determine its surface area and pore size distri-bution [122]. Besides this, their catalytic activity is also stronglydependent on their swelling properties because the swelling capac-ity limits reactant accessibility to the acid sites and affects theiroverall activity [123]. Common types of acidic ion-exchange resinsare Amberlyst-15, Amberlyst-35 and Nafion SAC-13.

Cation-exchangeable layered transition metal oxides are oneof the attractive solid acid catalysts due to their enriched ionexchangeable sites within the interlayer space. The layeredmetal oxide of HNbMoO6·nH2O and HTaMoO6 were reported asfavourable acid catalysts for various reactions [124–126]. As animportant type of solid catalyst, niobic acid (e.g., Nb2O5·nH2O) hasattracted much attention in dehydration, hydration, esterification,hydrolysis, condensation, and alkylation reactions [127–133] for itsunique acidity in the presence of water. Recently, lot of efforts arecontinuously focused on the catalytic applications of layered niobicacids because of their nanosheet crystal structure and facile prepa-ration via simply ion exchange of protons from their correspondingpotassium niobates [134,135]. Zhao et al. have successfully syn-thesized a family of ordered mesoporous phenol-formaldehyderesins (FDU-n, n = 14–16) with versatile mesostructures by usinghydrocarbon surfactants (P123 and F127), which offers a greatopportunity for synthesizing resins with functionalized sulfonicgroups [136–139]. Compared with mesoporous silica walls, organicframeworks of mesoporous resins have a hydrophobic feature. Wuand co-workers have prepared SO3H-functional FDU-type meso-porous phenol-formaldehyde resins for the first time, [140] whichgives superior catalytic activities in Beckmann rearrangement ofcyclohexanone oxime and condensation of bulky aldehydes withalcohols. These solid acids have high surface areas (upto 539 m2/g)and controllable hydrophobicity, but their acidic concentration isstill blocked by the limitation of sulfonation in phenolic rings due tothe strong steric hindrance. Therefore, SO3H-functionalized porousorganic materials with large surface area and high concentration ofsulfonic groups as well as good stability are highly desirable. It isreported that mesoporous polydivinylbenzenes can be functional-ized with relatively high concentration of sulfonic groups due togood swelling feature compared with mesoporous FDU-14 [141].

Some important reactions catalyzed by solid ion-exchangeresins are presented below:

Kidwai et al. reported a one-pot, three-component couplingreaction of aldehydes, amines and alkyne (A3-coupling) via C-Hactivation using perflorinated resin sulfonic acid (Nafion®NR50) forthe synthesis of propargylamines (Scheme 30) [142].

The catalyst activity of ion-exchange resins such as niobiumphosphate and Amberlyst-35 were evaluated in the acetalizationof hexanal with 2-ethyl-hexanol (Scheme 31) [143].

Yang et al. reported layered niobic acids as solid acid catalystsfor the selective hydration of ethylene oxide [144]. Self exfolia-tion behaviour of Nb3O8

− nanosheets during hydration was foundto be one of the most crucial factors for its high monoethyleneglycol selectivity. Narsaiah reported the use of amberlyst-15® for


the preparation of �-enamino compounds from 1,3-diketones andamines (Scheme 32) [145].




H2O++

H

O

OHOONiobium pho sphate

Ambe rlyst-35

Scheme 3

R"NH2+Amberl yst- 15

R.T.R R'

O O

R R'

NHR"O

Scheme 32.

ROHSnCl2/HAP

+

HO O

HO OHOor H3C

OHOR

O

H2O+

aitasc[

3

niahFtrfsopaf[tHpb

ratoa

3

a

OH

Scheme 33.

A novel melamine-formaldehyde resin (MFR) supported solidcid with Lewis and Brønsted acid sites was synthesized by themmobilization of acidic ionic liquid and cuprous ion on MFR andhe catalytic performance of this solid acid was examined for thecetalization of carbonyl compounds and diols. The catalysis resultshowed that the cooperation of Lewis and Brønsted acid sites in theatalytic procedure increased the catalytic efficiency of the catalyst146].

.4. Hydroxyapatite based solid acids

Hydroxyapatite (HAP; Ca10(PO4)6(OH)2) is a highly abundantatural material being the major component of teeth and bones. It

s also considered to have durable acid–base properties and highdsorption capacity making it a promising support material. Thisas been demonstrated in the use of HAP-supported Lewis acids inriedel–Crafts alkylations [147] and more recently in Michael addi-ion of indoles to electron-deficient olefins [148]. Solhy et al. [149]eported fluoroapatite and hydroxyapatite supported zinc chlorideor a wide range of transesterification reactions. The primary rea-on for the activity of ZnCl2–HAP is the well dispersed Lewis acidn the support. In addition to this, supported FeCl3 has also beenroved to be an efficient Lewis acid catalyst [150] and hydroxyap-tite supported tin(II) chloride and tin(IV) chloride were reportedor the transformation of trioses in alcohols to yield alkyl lactates151] (Scheme 33). The activity of SnCl2/HAP can be attributed tohe stronger ability of tin(II) to exchange with calcium(II) in theAP leading to a stable and active structure. Because tin(IV) is moreositive than calcium(II) it is unlikely to remain in the HAP withoutreaking the charge balance.

Deng et al. [152] reported a novel procedure for the prepa-ation of secondary or tertiary amines by one-pot reductivemination of carbonyl compounds using sodium borohydride inhe presence of a magnetically recoverable sulfonic acid supportedn hydroxyapatite-encapsulated-�-Fe2O3 [�-Fe2O3@HAP-SO3H]t room temperature.


.5. Zirconia based solid acids

Although silicas and aluminosilicates have attracted the greatttention as oxide supports, there are other materials which offer

1.

the necessary properties of high surface area, chemical and ther-mal stability, and an active surface. Zirconia is one such materialwhose surface is derivatized with sulfated functions, thus giving“sulfated zirconia” (SZ) which is an interesting and useful solidacid [153,154]. Normal SZ is microporous in nature, making it suit-able for traditional vapour-phase applications but less amenableto liquid phase reactions. However, mesoporous versions can bemade. Both the surface area and the sulfate loading of SZ materialsdecrease on increasing the calcination temperatures especially at>550 ◦C [155]. Catalysts calcined between 500 and 600 ◦C and sub-sequently cooled in a desiccator exhibited only Brønsted acid sites.It is believed that this is due to the rapid adsorption of water fromthe atmosphere or from organic solvents or substrates on coolingwhich converts Lewis into Brønsted acid sites. Practically, it meansthat for liquid-phase organic reactions carried out in normal labo-ratories or manufacturing plants, SZ can be expected to behave asa solid Brønsted acid.

The Brønsted acidity of SZ combined with its mesoporosityand its excellent thermal stability makes it a very good candi-date for aromatic alkylations using long chain alkenes, which areprone to competitive polymerisation easily, causing pore block-age (such heavy organics can be more easily removed from a morethermally stable material) [156]. By comparing mesoporous opti-mally activated SZ with AlCl3 (the traditional catalyst for suchreactions) and HY zeolite (one of the modern catalysts for the reac-tion), it has been shown that SZ has activity comparable to AlCl3and is more active than HY. Although sulfated zirconia provides acatalyst that is solid and easier-to-handle than the corrosive liq-uid acids usually used. but supported SZ has been developed toreduce costs, improve surface properties and find a mechanicallystable form of sulfated zirconia suitable for large scale industrialprocesses. Common supports for SZ found in the literature areSiO2, [157–159] �-Al2O3, [158,159] and zeolites [160]. The cat-alytic activity of these supported catalysts has been studied for thefollowing reactions: n-octane hydroisomerisation, [161] etherifica-tion, [157] hexane conversion, [158] 1-butene isomerisation, [160]and n-butane isomerisation [159]. Some recent examples of organicreactions catalyzed by zirconia are presented below:

Sulfated zirconia supported on MCM-41 has been recentlyreported for the benzylation of benzene [162]. It has been shownthat the support stabilized the coordinated sulfate groups on thesurface and the pore volume and specific surface area data showeda slight and uniform decrease on both the surface area and the porevolume with an increase of the zirconium oxide contents over theMCM support surface. These results showed that most of the ZrO2contents are available inside the pores and well dispersed on thesurface. At samples with sulfate zirconia content higher than 40%,sharper decrease of the pore volume and surface area occurred. Inthis case the decrease in the pore volume was observed markedlyand the sulfur contents as well decreased and this decrease in thesulfur contents may be attributed to the migration of most of thesulfate groups from the MCM pores to the surface which facilitate


the decomposition during thermal calcination. This strongly indi-cated that the support stabilized the coordinated sulfated groups.The catalyst has also been reported for the synthesis of coumarinsunder thermal and microwave irradiation [163] (Scheme 34).




SZThermal/MW

C2H5OH++R OH

H3C OC2H5

O O

O O

CH3

R

eme 3

aLvsaacoPZ(oms

aacpacfdatfoncenbotl

3

raLcawacrawcct

bmi

Sch

Fibrous sulfated zirconia has been reported as an efficient solidcid catalyst for the esterification of acetic acid with n-butanol byiao and co-workers [164]. Qi et al. have reported efficient con-ersion of fructose to 5-hydroxymethylfurfural in the presence ofulfated zirconia in ionic liquids [165]. A series of magnetic solidcid nano-catalysts, ZrO2–Al2O3–Fe3O4 (ZAF) [166] were designednd prepared through a facile co-precipitate approach and theiratalytic behaviour was investigated via esterification, synthesisf bis-indolylmethanes, Hantzsch reaction, Biginelli reaction andechmann reaction. It has been shown that the composition ofAF catalysts had an obvious impact on the specific surface areaSBET). There was an appreciable variation in SBET with the increasef ZrO2–Al2O3 contents and on the other hand, addition of alu-ina component to the catalysts resulted in an increase in specific

urface area.Recently synthesis of mesoporous borated zirconia as an

cid–base bifunctional solid catalyst using aqueous zirconiummmonium carbonate complex and borax in presence ofetyltrimethylammonium bromide was reported by Sinhamaha-atra and co-workers [167]. It has been found that the total aciditynd basicity of the borate modified zirconia was more than pure zir-onia. The acidity increases from 0.94 to 1.55 mmol g−1 and basicityrom 0.61 to 0.81 mmol g−1. The acid-base character of zirconia wasirectly correlated to the surface area as it increases with surfacerea because of the increment of accessible active sites. In the syn-hesized BZ samples the total acidity per square meter increasesrom 0.0058 to 0.0066 mmol m−2 because boron with an emptyrbital pulls the electron cloud from the oxygen of ZrO2 and theegative charge generated on boron then diffuses into boron oxideage by the resonance between the lone pair of oxygen and thempty orbital of boron which enhances the Lewis acidity. However,o significant change was observed in basicity per square meterecause basicity originates only from the bridged oxygen (Zr-O-Zr)f the zirconia cages and borate species do not have any contribu-ion to the basicity except for the fact that increased surface areaeads to increase in basicity.

.6. Carbon based solid acids

Other promising solid acid catalysts are carbon-based mate-ials bearing sulfonic acid groups. Carbon-based solid sulfoniccid catalysts were first described by Hara and co-workers [168].ately they employed sucrose as a carbon precursor to preparearbon-based sulfonic acid catalysts and investigated their cat-lytic properties [169–171]. Templated porous carbon materialsere sulfonated and used as solid acid catalysts as well [172,173]

nd good stability and catalytic activity was observed when thesearbons were prepared at high temperatures. Tian and co-workerseported sulfonated polypyrrole nanospheres [174,175] solid acidsnd evaluated their catalytic activity for esterification of methanolith acetic acid. Recently, it was found that sulfonated amorphous

arbon when dispersed over silica materials leads to sulfonatedarbon/silica composites having more stability, activity and selec-ivity.


Nakajima et al. [176] prepared sulfonated amorphous car-on/silica composites for the selective dimerization of �-ethylstyrene. Partial carbonization and sulfonation of d-glucose

mpregnated SBA-15 resulted in the formation of a carbon/SBA-15

4.

composite where SO3H-bearing carbon with large surface area wasincorporated into the mesopores of SBA-15. Bulky SO3H-bearingcarbon material prepared simply by the partial carbonization andsulfonation of d-glucose does not catalyze the dimerization of�-methylstyrene at all because of the small surface area, whilethe carbon/SBA-15 composite exhibits remarkable catalytic perfor-mance (conversion and selectivity) for the production of dimericpentene derivates from �-methylstyrene. The selective productionof unsaturated dimers over the carbon/SBA-15 composite can beattributed to blocking of the intramolecular Friedel–Crafts alkyl-ation on SO3H-bearing carbon with large surface area.

Sulfonated carbon–silica composites with surface areas of over600 m2/g and pore sizes of 1.5–2.2 nm were prepared by incom-pletely carbonizing sucrose dispersed on MCM-48 and sulfonatingthe obtained carbon/MCM-48 composites [177]. The catalytic activ-ities of these composites were studied in the esterification ofacetic acid with n-butyl alcohol. The pore sizes and catalytic activ-ities of the sulfonated carbon-silica composites were adjustableby changing the amount of sucrose loadings and the compos-ites exhibited enhanced hydrothermal stability and amphiphilicproperty. When the sucrose loading was close to the monolayerdispersion capacity of sucrose on MCM-48 (1.1 g sucrose/gMCM-48), the resulting sulfonated carbon-silica composites exhibitedsurface areas of 700–724 m2/g and n-butyl acetate yields of90.4–98.7%.

Degradation of cellulose into high yield of glucose has also beenreported in the presence of sulfonated silica/carbon nanocompos-ites [178]. The high catalytic performance was attributed to (i) thepresence of strong, accessible Brønsted acid sites and (ii) the hybridsurface structure constituted by interpenetrated silica and carboncomponents facilitating the adsorption of �-1,4 glucan on the solidcatalyst. Wang et al. reported sulfonated ordered mesoporous car-bon acid catalysts having an acid density of 1.93 mmol H+ g−1 andimpressive catalytic activity [179].

Graphene has excellent mechanical properties, a large surfacearea and a distinctive two-dimensional structure, [180,181] provid-ing an ideal platform to anchor a large amount of acidic functionalgroups with accessible active sites. Ji et al. prepared sulfonatedgraphene as a water-tolerant solid acid catalyst and evaluated itscatalytic activity for hydrolysis of ethyl acetate. It has been shownthat microstructure of the graphene sheets was not destroyed bythe sulfonate reaction and the reactants can easily access the activesites on both sides of the two dimensional graphene sheets. Thoughthe two-dimensional structure may cause diffusion hindrance dur-ing the reaction, the reduced graphene sheets are small enough(about 5 �m × 1 nm in size) to be well dispersed under stirringconditions [182].

Rayoo et al. prepared sulfonated mesoporous SiO2-TiO2-SO3Hcatalyst by simple chelation of a benzene disulfonate compoundto the Ti ion and its catalytic activity was evaluated for the ester-ification reactions of acetic acid with ethanol. The remarkablecatalytic activity of the developed catalyst could be attributed tothe enhanced acidic strength of the catecholic sulfonic acid due tothe presence of a neighbouring electron withdrawing phenyl group


as well as the increased acid density inside the large pores by twoacid groups in one molecule of catecholic acid [183].

Some recent sulfonated carbon based solid acid catalysts andtheir applications are presented below:


ARTICLE ING ModelCATTOD-9037; No. of Pages 18

P. Gupta, S. Paul / Catalysis To

RCHO Ac2O ROAc

OAc+

CSC-Sta rSolv ent- free,

60 oCR-XH Ac2O R-XAcCSC-Star

X = NH, O, S

Solvent-free ,

60 oC

bfFmsabw

h[fitblmdbgf[ookaa

tocsp

cOoa

the prepared carbonaceous materials. The presence of these groupspromote the adsorption of cellulose and water molecules through

Scheme 35.

Lin and co-workers [184] reported a nanocage carbon bearingenzene sulfonic acid catalyst and evaluated its catalytic activityor cross-aldol condensation of ketones and aromatic aldehydes.irst, the carbon nanocage material was synthesized with cage typeesoporous silica as inorganic template and sucrose as the carbon

ource and then the carbon nanocage material was treated with anqueous solution of sulfophenyl radicals which are easily generatedy reacting 4-aminobenzenesulfonic acid with isoamyl nitrite inater.

A sulfonated carbon catalyst with mesoporous structure andigh surface area was successfully prepared Kitano and co-workers185]. The catalyst exhibited high catalytic performance for esteri-cation of acetic acid and benzylation of toluene. It has been shownhat the catalytic activity was independent of specific surface areaut dependent on acid density and the samples carbonized at

ower temperatures can incorporate large amounts of hydrophilicolecules such as ethanol into the carbon bulk due to the high

ensity of hydrophilic functional groups bound to the flexible car-on sheets. This incorporation provides good access to the –SO3Hroups [185] in the carbon material resulting in high catalytic per-ormance despite the relatively low specific surface area. Liang et al.186] reported novel carbon solid acid synthesized by the treatmentf 2-hydroxyethylsulfonic acid and starch and the catalytic activityf the catalyst was investigated for acetalization of aldehydes andetones. Xu and co-workers [187] reported sucrose char sulfoniccid for one-pot three component Mannich reaction of ketones,romatic aldehydes and amines in ethanol.

Recently, a solid acid was prepared from glucose-starch mix-ure [188] and its catalytic activity was evaluated for esterificationf oleic acid with methanol. Moreover, carbon/mesoporous silicaomposite [189] functionalized with sulfonic groups was synthe-ized by vapour phase sulfonation and used for the esterification ofalmitic acid with methanol.

We have reported sulfonated carbon/silica composites forhemoselective protection of aldehydes as 1,1-diacetates and for N,


and S acylations [190a] (Scheme 35) and for the one-pot synthesisf Hantzsch 1,4-dihydropyridines, 2,4,5-trisubstituted imidazolesnd 2-arylbenzimidazoles [190b] (Scheme 36).

O

NH4OPh

Ph

O

O

N

NH

CSC-SEthanol,

R H

O

Ph

PhR

N

NH

CSC-Star80 oCWater,

NH2

NH2R

Scheme 3

PRESSday xxx (2014) xxx–xxx 13

We have also reported [190c] amorphous carbon/silica com-posite functionalized lewis acids for one pot synthesis of1,2,4,5 tetrasubstituted imidazoles, 3,4-dihydropyrimidin-2(1H)-ones, Michael addition of indole to �,�-unsaturated ketones(Scheme 37) and ionic liquid coated sulfonated carbon/silica com-posites [190d] for organic syntheses in water (Scheme 38).

Lignin is the second-most abundant natural organic materialafter cellulose, and the richest aromatic organic biopolymer, hashigh carbon content and is used as a precursor for activated carbon.Liang et al. [191] prepared solid acid from lignin and its catalyticactivity was examined for the esterification of acetic acid withethanol and hydration of 2,3-dimethyl-2-butene as probe reac-tions. It has been reported that the catalyst showed much higheractivities than Amberlyst 15 ion-exchange resin and sulfonatedcarbon for esterification. However, compared with Amberlyst 15ion-exchange resin or sulfonated carbon, the lignin-based solidacid catalyst has low concentration of sulfonic acid groups, so thehigh catalytic activities over the lignin-based catalyst should bedirectly related to the contribution of the abundant macroporosity.The abundant macroporosity has an advantage for mass transferachieving good accessibility for reactants in solution to sulfonic acidgroups. On the other hand, the lignin-based solid acid catalyst hadthe lowest activities for the hydration of 2,3-dimethyl-2-butenethan the other solid acid catalysts. The sulfonated carbon cata-lyst exhibited the highest activity for hydration attributed to itshydrophobic nature.

Pua et al. [192] prepared a solid acid catalyst from Kraft ligninand used it to synthesize biodiesel from high-acid value Jatrophaoil. The higher conversion rates were due to the high density ofthe acid (–SO3H) sites from sulfonation in the pores of activatedcarbon by treatment with phosphoric acid and pyrolysis. More-over, sulfonated ordered nanoporous carbon (CMK-5-SO3H) [193]has been used for the synthesis of perimidines by Alinezhad et al.(Scheme 39).

A cellulose-derived carbonaceous solid acid catalyst [194]that has superparamagnetism was synthesized by incompletehydrothermal carbonization of cellulose followed by Fe3O4 graftingand –SO3H group functionalization. The as-prepared superpara-magnetic carbon catalyst contained –SO3H, –COOH and phenolic–OH groups and exhibited good catalytic activity for the hydrol-ysis of cellulose in either an ionic liquid phase or aqueous phase.The catalyst was more efficient than other solid catalysts such asresins, sulfonated activated carbons, heteropolyacids and magneticsulfonated silica materials in either ionic liquid or water which wasattributed to the presence of phenolic –OH or –COOH groups in


hydrogen bonding resulting in efficient hydrolysis of cellulose into�-1,4-glucan and glucose. A new approach for the synthesis of

CSC-Star

60 oCSolvent-free,NH

RCO2EtOEt EtO2C

NH4OAc OH

Ac,tar

80 oC

6.




NH4OAc

Ethanol, 80 oC

N

N

Ph

PhR2

R1

CSC-St ar- SO3AlCl280 oCCH3CN,

R3NH2,

NH

CSC-Star- SO3AlCl2

Toluene, 110 oC

NH

Ar2

Ar1 O

R1

R2O

H2N NH2

O

O

O

O

O

NH

NH

O

R HO

Ph

Ph

O

O

CSC-Star- SO3AlCl2

Scheme 37.

CSC- Star- Glu-IL2Water, R.T.

X= CN, COOE t

R1 R2

O CNX NC R1

X R2

R3NH2

CSC-Star-Glu-I L2wate rNaBH4,

R

NHR3

MW, 60 oC

CSC-Star- Glu -IL2Water, 1 00 oC

NH

ArR2

O

Ar CH CHR1 =

NH

)(

eme 3

saucg(t

Sch

pirooxindoles from isatin, malononitrile, and 1,3-dicarbonyls tofford a wide range of spiro[4H-pyran-3,3′-oxindole]derivativessing glycerol-based carbon-sulfonic acid was reported by Rao ando-workers [195] (Scheme 40). The catalyst was prepared from bio-


lycerol (a by product of biodiesel) and also from glycerol pitchwaste from fat splitting industry) by in situ partial carboniza-ion and sulfonation in a one-pot operation. In another approach,

NH2 NH2 HN NH

R1 R2

CMK-5-SO3H

EtOHR1R2CO+

R1=Aryl, AlkylR2=H, Alkyl

Scheme 39.

NH

O

O

CN

CN O

O

Carbon-SO3H

EtOH, reflux

O

NH2

O

NH O CN

+

Scheme 40.

1 R2

8.

Gangadhar et al. [196] used glycerol based carbon-sulfonic acidcatalyst for acetylation reactions.

Lou and co-workers [197] developed a solid acid catalyst by sul-fonation of incompletely carbonized bagasse and used it for thesynthesis of biodiesel. It was shown that the catalytic and texturalproperties of the bagasse-derived catalyst were significantly influ-enced by the preparation conditions especially carbonization andsulfonation temperatures. Under the optimal preparation condi-tions (648 K carbonization for 0.5 h and 423 K sulfonation for 15 h),the resulting catalyst had the highest density of –SO3H groups andshowed the highest catalytic activities for esterification and trans-esterification reactions.

The Fe3O4@C core–shell magnetic nanoparticles with an aver-age size of about 190 nm were synthesized via a one-potsolvothermal process using ferrocene as a single reactant [198].The sulfonic acid-functionalized Fe3O4@C magnetic nanoparticleswere obtained by grafting the sulfonic groups on the surface ofFe3O4@C nanoparticles to produce magnetically recyclable solidacid catalysts and their catalytic activity was examined through thecondensation reaction of benzaldehyde and ethylene glycol. It wasshown that the mesoporous carbon layer covered on the surface ofFe3O4 cores cannot only stabilize the Fe3O4 MNPs against aggrega-tion and prevent oxidation of the Fe3O4 MNPs but can also be coor-dinated or grafted with –SO3H groups. Also, the porous structure


and large surface area of the catalyst could be responsible for graft-ing –SO3H groups and making reactants come into contact withacid sites with high efficiency. Recently sawdust, a biomass waste,was converted into a magnetic porous carbonaceous (MPC) solid




OH

OH

O OO

Acid cataly st

363 K+

O OHOH OH

OHO

OAcid cataly st

423 K, DMS O

O O

HO

HO

O OH

HOHO

HO

Acid cataly st

353 K, H2O

O

HOOH

HO

OH

HO

O

HO OHOH

HOHO

+

eme 4

acstca

otcfhtwcotchwwsttmsmtocbasanwaah

4

mBrtstt

OH OH

Sch

cid catalyst [199] by an integrated fast pyrolysis–sulfonation pro-ess (Scheme 41) and the resultant magnetic solid acid having highurface area of 296.4 m2/g was used for three acid-catalyzed reac-ions: esterification, dehydration, and hydrolysis. The favourableatalytic performance in all three reactions was attributed to thecid’s high strength with 2.57 mmol g−1 of total acid sites.

The important factor that determines the catalytic performancef these amorphous carbon bearing –SO3H catalysts (CSA) ishe carbonization temperature of the starting material e.g. onlyomplex polymer containing aromatic compounds are obtainedrom the carbonized matter at low temperatures. On the otherand, soluble sulfonated species are produced from sulfonatinghe incompletely carbonized matter [168,200]. Furthermore,hen carbonized at moderate temperatures (400–450 ◦C), these

atalysts possess three –OH groups, three –SO3H groups andne –COOH group against the single functional group commono conventional solid acid catalysts. This distinguishing featureontributes to their greater catalytic performance. Interestingly,igh carbonization temperatures (>450 ◦C) enhances carbon net-ork development without the –COOH and phenolic –OH groupshich in turn, increases the cross-linking between the carbon

heets and reduces the amounts of the –SO3H groups bondedo the carbon sheets. CSA catalysts carbonized at ≥550 ◦C havehe ability to absorb the hydrophilic molecules from the reacting

edium and bonding between the –SO3H groups and the carbonheets positions the former where the absorbed or incorporatedolecules have no direct access to the Brønsted acid sites. Hence,

he absorbed hydrophilic molecules hinder the sufficient numberf the –SO3H groups from the reacting species which leads to pooratalytic activity. This phenomenon was reported for all the CSAearing –SO3H catalyzed reactions [168,200,201]. Higher activitynd lower amounts of catalysts required (compared with any otherolid acid catalyst), stability, and reusability are the promisingttributes of these CSA catalysts. But because of their organicature these catalysts are susceptible to poisoning in polar mediahile the conventional regeneration technique (calcination) is not

pplicable on them and one strategy currently being explored tovoid or eliminate this limitation is the use of enhanced surfaceydrophobization.

. Evaluation of acidity of solid acids

In 2009, Iglesia et al. [202] reported a rigorous method to esti-ate the deprotonation energy (DPE) and acid strength for solid

rønsted acids with uncertain structure using rate constants foreactions involving cationic transition states. The rates and selec-


ivities of chemical reactions catalyzed by acid sites within porousolids depend on the stabilities of ion-pairs at the transition stateshat mediate the kinetically-relevant elementary steps withinheir respective catalytic sequences. The rates and selectivities for

1.

alkanol dehydration, homologation, isomerisation of alkenes andcycloalkenes on polyoxometalate and zeolitic Brønsted acids showthat chemical reactions sense acid strength as a result of differencesin the amount and localization of cationic charges in the relevantprecursors and in the ion-pairs at transition states. Acid strengthrigorously defined in terms of deprotonation energies determinesthe extent to which electrostatic interactions stabilize both pre-cursors and transition states and its catalytic consequences aregreatest when uncharged precursors lead to ion-pairs at transitionstates. Such sensitivity to acid strength is generally unrelated tothe facile or demanding nature of a particular chemical reactionwhich reflects instead the chemical stability of gaseous analogsof the cationic transition states. Solvation by confinement withinmicroporous voids is mediated by van der Waals forces which sup-plement the electrostatic stabilization of cationic transition states.The effects of confinement on rates and selectivities depend on dif-ferences in size between molecular precursors and their respectivetransition states, because size determines their respective abilityto contact the walls within confining voids. These studies exploitthe use of polyoxometalate and zeolitic acids because their knownand stable structures allow rigorous benchmarking of theory andexperiments in a manner that confirms mechanistic interpretationsof reactivity and the relevance of the electrostatic componentsof deprotonation energies as theoretical proxies for acid strengthand for its catalytic consequences. These studies and insightsalso suggest a reactivity-based ranking of solids rigorously basedon acid strength and provide useful protocols to assess the acidstrength of materials with uncertain or non-uniform structuresand to infer, in some cases, the nature of their active sites.

5. Future prospects of solid acids

Consequently, the era of catalysis research which was char-acterized primarily by trial-and-error is becoming history [203].Techniques such as quantum mechanics calculations, density func-tional theory simulation, solid-state nuclear magnetic resonance,in situ fluorescence microscopy and computational- real-timetechnology are being experimented to decipher the in-depths ofheterogeneous catalysis and surface science [204,205]. Achievingthese fundamental insights into the mechanisms of catalysis viabreakthroughs in theoretical insights and computational methodswill enhance predicting catalysts performance under real reactionconditions. These important tools will in turn be utilized in thedesign of novel (solid acid) catalysts and the control of catalytic pro-cesses [168]. Determining the active sites of surface reactions, thebarrier(s) encountered in such reactions and the rate at which they


occur even within picoseconds would be facilitated. These mightinvolve combining such techniques and utilizing probe moleculesaugmented with multifarious nuclei such as 1H, 13C and 31P forinvestigating surface acidities of the solid acid catalysts [206].


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. Conclusions

Compared with liquid acid catalysts, solid acid catalysts haveistinct advantages in recycling, separation, and environmentalriendliness. Besides specific surface area, pore size and pore vol-me, the active site concentration and acidic type are importantactors for solid acid performance. Solid acid catalysts should have

large number of acid sites, good affinity for the reactant substratesnd good thermal stability. Catalyst composition, porosity, and sta-ility in the presence of water are other important properties forolid acids.

eferences

[1] P.T. Anastas, J.C. Warner (Eds.), Green Chemistry: Theory and Practice, OxfordUniversity Press, Oxford, 1998.

[2] P.T. Anastas, T.C. Williamson (Eds.), Green Chemistry: Frontiers in ChemicalSynthesis and Processes, Oxford University Press, Oxford, 1998.

[3] P.T. Anastas, M.M. Kirchhoff, Acc. Chem. Res. 35 (2002) 686.[4] P.T. Anastas, L.G. Heine, T.C. Williamson (Eds.), Green Chemical Syntheses and

Processes, American Chemical Society, Washington DC, 2000.[5] P.T. Anastas, C.A. Farris (Eds.), Benign by Design: Alternative Synthetic Design

for Pollution Prevention, American Chemical Society, Washington DC, 1994.[6] J.H. Clark, D.J. Macquarrie, Handbook of Green Chemistry and Technology,

Blackwell, Abingdon, 2002.[7] A.S. Matlack, Introduction to Green Chemistry, Marcel Dekker, New York,

2001.[8] M. Lancaster, Green Chemistry:, An Introductory Text, Royal Society of Chem-

istry, Cambridge, 2002.[9] J.H. Clark (Ed.), The Chemistry of Waste Minimization, Blackie, London, 1995.

[10] C.G. Brundtland, Our Common Future, The World Commission on Environ-mental Development, Oxford University Press, Oxford, 1987.

[11] R.A. Sheldon, C. R. Acad. Sci. Paris, IIc, Chimie Chem. 3 (2000) 541.[12] P.T. Anastas, M.M. Kirchhoff, T.C. Williamson, App. Catal. A: Gen. 221 (2001)

3.[13] K. Tanabe, W. Hölderich, Appl. Catal. A: Gen. 181 (1999) 399.[14] R.A. Sheldon, R.S. Downing, Appl. Catal. A: Gen. 189 (1999) 163.[15] R.A. Sheldon, H.V. Bekkum (Eds.), Fine Chemicals through Heterogeneous

Catalysis, Wiley-VCH, Weinheim, 2001.[16] T. Cseri, S. Bekassy, F. Figeuras, E. Cseke, L.C. Demenorval, R. Dunarte, Appl.

Catal. A: Gen. 132 (1995) 141.[17] (a) J.H. Clark, D.J. Macquarrie, J. Chem. Soc. Dalton Trans. (2000) 101;

(b) P. Laszlo, Preparative Chemistry using Supported Reagents, AcademicPress, London, 1987;(c) P.T. Tanev, T.J. Pinnavaia, Science 267 (1995) 865.

[18] J.H. Clark, K. Martin, A.J. Teasdale, S.J. Barlow, Chem. Commun. (1995) 2037.[19] E.D. Matveeva, M.V. Shuvalov, N.S. Zefirov, Russ. Chem. Bull., Int. Ed. 60 (2011)

242.[20] M.R. Saidi, Y. Pourshojaei, F. Aryanasab, Synth. Commun. 39 (2009) 1109.[21] K. Wilson, D.J. Adams, G. Rothenberg, J.H. Clark, J. Mol. Catal. A: Chem. 159

(2000) 309.[22] B. Sadeghi, B.F. Mirjalili, M.M. Hashemi, J. Iranian Chem. Soc. 5 (2008) 694.[23] A. Lambert, G. Carr, J.H. Clark, D.J. Macquarrie, New J. Chem. 24 (2000) 485.[24] F.M. Moghaddam, A.A.R. Rad, H.Z. Boinee, Synth. Commun. 34 (2004) 2071.[25] A. Keivanloo, M. Bakherad, B. Bahramian, S. Baratnia, Tetrahedron Lett. 52

(2011) 1498.[26] (a) R. Gupta, M. Gupta, S. Paul, R. Gupta, Can. J. Chem. 85 (2007) 197;

(b) K. Niknam, A. Hasaninejad, Madihe Arman, Chin. Chem. Lett. 21 (2010)399;(c) K. Niknam, M.A. Zolfigol, D. Saberia, H. Molaeea, J. Chin. Chem. Soc. 56(2009) 1257.

[27] A.K. Chakraborti, R. Gulhane, Chem. Commun. 9 (2003) 1896.[28] V.T. Kamble, V.S. Jamode, N.S. Joshi, A.V. Biradar, R.Y. Deshmukh, Tetrahedron

Lett. 47 (2006) 5573.[29] A. Misra, P. Tiwari, G. Agnihotri, Synthesis (2005) 260.[30] G. Agnihotri, A.K. Misra, Tetrahedron Lett. 47 (2006) 3653.[31] T.V. Kamble, R.K. Kadam, S.N. Joshi, B.D. Muley, Catal. Commun. 8 (2007) 498.[32] M. Maheswara, V. Siddaiah, G.L.V. Damu, C.V. Rao, ARKIVOC II (2006) 201.[33] L. Nagarapu, V. Paparaju, G. Pathuri, S. Kantevari, R.R. Pakkiru, R. Kamalla, J.

Mol. Catal. A: Chem. 267 (2007) 53.[34] S. Kantevari, S.V.N. Vuppalapati, D.O. Biradar, L. Nagarapu, J. Mol. Catal. A:

Chem. 266 (2007) 109.[35] S. Kantevari, R. Bantu, L. Nagarapu, J. Mol. Catal. A: Chem. 269 (2007) 53.[36] H.R. Shaterian, H. Yarahmadi, M. Ghashang, Tetrahedron 64 (2008) 1263.[37] A.K. Chakraborti, S.V. Chankeshwara, Org. Biomol. Chem. 4 (2006) 2769.[38] M. Nasar-Esfahani, M. Montazerozohori, T. Gholampour, Chin. J. Chem. 29

(2011) 123.


[39] D. Ramesh, S. Rajaram, M. Narasimhulu, T.S. Reddy, K.C. Mahesh, G. Manasa,Y. Venkateswarlu, Chin. J. Chem. 29 (2011) 2471.

[40] A. Corma, C. Opin, Solid State Mat. Sci. 2 (1997) 63.[41] J.M. Riego, Z. Sedin, J.M. Zaldivar, N.C. Marziano, C. Tortato, Tetrahedron Lett.

37 (1996) 513.

PRESSday xxx (2014) xxx–xxx

[42] G.A. Olah, R. Molhotra, S.C. Narang, J. Org. Chem. 43 (1987) 4628.[43] M.A. Zolfigol, Tetrahedron 57 (2001) 9509.[44] P. Salehi, M. Dabiri, M.A. Zolfigol, M.A. Bodaghi, J. Braz. Chem. Soc. 15 (2004)

773.[45] B.F. Mirjatili, M.A. Zolfigol, A. Bamoniri, Bull. Korean Chem. Soc. 25 (2004) 865.[46] B.F. Mirjalili, M.A. Zolfigol, A. Bamoniri, Molecules 7 (2002) 751.[47] B.F. Mirjalili, M.A. Zolfigol, A. Bamoniri, A. Zarei, J. Chin. Chem. Soc. 51 (2004)

509.[48] M.A. Zolfigol, A. Bamoniri, Synlett (2002) 1621.[49] (a) M.A. Zolfigol, J.M. Baltork, B.F. Mirjalili, A. Bamoniri, Synlett (2003) 1877;

(b) P. Salehi, M.A. Zolfigol, F. Shirini, M. Baghbanzadeh, Curr. Org. Chem. 10(2006) 2171.

[50] Z. Zhang, S. Sui, F. Wang, Q. Wang, C.U. Pittman Jr., Energies 6 (2013) 4531.[51] (a) K. Venkateswarlu, B. Ravikanth, Chem. Pharm. Bull. 56 (2008) 366;

(b) J.E. Castanheiro, L. Guerreiro, I.M. Fonseca, A.M. Ramos, J. Vital, Stud. Surf.Sci. Catal. 174 (2008) 1319.

[52] B. Karimi, M. Khalkali, J. Mol. Catal. A: Chem. 232 (2005) 113.[53] A. Karam, J.C. Alonso, T.I. Gerganova, P. Ferreira, N. Bion, J. Barrault, F. Jérôme,

Chem. Commun. (2009) 7000.[54] P.L. Dhepe, M. Ohashi, S. Inagaki, M. Ichikawa, A. Fukuoka, Catal. Lett. 102

(2005) 163.[55] S.-Y. Chen, T. Yokoi, C.-Y. Tang, L.-Y. Jang, T. Tatsumi, J.C.C. Chan, S. Cheng,

Green Chem. 13 (2011) 2920.[56] G.H. Mahdavinia, M.M. Ghanbari, H. Sepehrian, F. Kooti, J. Iranian Chem. Res.

3 (2010) 117.[57] H. Naeimi, Z.S. Nazifi, J. Nanopart. Res. 15 (2013) 2026.[58] D. Lai, L. Deng, J. Li, B. Liao, Q. Guo, Y. Fu, ChemSusChem. 4 (2011) 55.[59] H.N. Lim, M.A. Yarmo, N.M. Huang, P.S. Khiew, W.S. Chiu, J. Phys. Sci. 20 (2009)

23.[60] E.-P. Ng, S.N.M. Subaria, O. Marieb, R.R. Muktic, J.-C. Juand, Appl. Catal. A: Gen.

450 (2013) 34.[61] F. Liu, J. Sun, L. Zhu, X. Meng, C. Qi, F.-S. Xiao, J. Mater. Chem. 22 (2012) 5495.[62] (a) M. Hajjami, F. Ghorbani, F. Bakhti, App. Catal. A: Gen. 470 (2014) 303;

(b) K. Niknam, D. Saberi, M.N. Sefat, Tetrahedron Lett. 50 (2009) 4058;(c) K. Niknam, D. Saberi, M. Mohagheghnejad, Molecules 14 (2009) 1915;(d) K. Niknam, D. Saberi, M. Sadegheyan, A. Deris, Tetrahedron Lett. 51 (2010)692;(e) K. Niknam, D. Saberi, M. Nouri Sefat, Tetrahedron Lett. 51 (2010) 2959;(f) K. Niknam, D. Saberi, M. Baghernejad, Chin. Chem. Lett. 20 (2009) 1444;(g) K. Niknam, R.M. Mohammadizadeh, S. Mirzaee, D. Saberi, Chin. J. Chem.28 (2010) 663;(h) K. Niknam, M.R. Mohammadizadeh, S. Mirzaee, Chin. J. Chem. 29 (2011)1417;(i) K. Niknam, F. Panahi, D. Saberi, M. Mohagheghnejad, J. Heterocyclic Chem.47 (2010) 292;(j) K. Niknam, D. Saberi, M. Baghernejad, Phosphorus, Sulfur Silicon 185 (2010)875;(k) K. Niknam, D. Saberi, H. Molaeea, M.A. Zolfigol, Can. J. Chem. 88 (2010)164.

[63] S.M. Ghaem Ahmadi-Ana, M. Baghernejad, K. Niknam, Chin. J. Chem. 30 (2012)517.

[64] (a) K. Niknam, D. Saberi, Appl. Catal. A: Gen. 366 (2009) 220;(b) F. Rohandeh, D. Saberi, K. Niknam, Iranian J. Catal. 1 (2011) 71;(c) S. Ghasemi, M. Baghernejad, K. Niknam, Iranian J. Catal. 3 (2013) 165;(d) S. Tayebi, M. Baghernejad, D. Saberi, K. Niknam, Chin. J. Catal. 32 (2011)1477;(e) Z. Tavakoli, M. Bagherneghad, K. Niknam, J. Heterocyclic Chem. 49 (2012)634;(f) N. Iravani, N.S. Mohammadzade, K. Niknam, Chin. Chem. Lett. 22 (2011)1151.

[65] (a) K. Niknam, D. Saberi, Tetrahedron Lett. 50 (2009) 5210;(b) M.-S. Shakeri, H. Tajik, K. Niknam, J. Chem. Sci. 124 (2012) 1025;(c) F. Rashedian, D. Saberib, K. Niknam, J. Chin. Chem. Soc. 57 (2010) 998;(d) K. Niknam, N. Jafarpour, E. Niknam, Chin. Chem. Lett. 22 (2011) 69;(e) K. Niknam, A. Deris, F. Naeimi, F. Majleci, Tetrahedron Lett. 52 (2011) 4642;(f) S. Tayebi, K. Niknam, Iran. J. Catal. 2 (2012) 69;(g) T. Rahi, M. Baghernejad, K. Niknam, Chin. Chem. Lett. 23 (2012) 1103;(h) K. Niknam, A. Jamali, M. Tajaddod, A. Deris, Chin. J. Catal. 33 (2012) 1312;(i) M.N. Sefat, A. Deris, K. Niknam, Chin. J. Chem. 29 (2011) 2361;(j) T. Rahi, M. Baghernejad, K. Niknam, Chin. J. Catal. 33 (2012) 1095.

[66] P. Gupta, V. Kumar, S. Paul, J. Braz. Chem. Soc. 21 (2010) 349.[67] I.V. Kozhevnikov, Chem. Rev. 98 (1998) 171.[68] A. Sivasamy, K.Y. Cheah, P. Fornasiero, F. Kemausuor, S. Zinoviev, S. Miertus,

ChemSusChem. 2 (2009) 278.[69] S. Zhang, Y.G. Zu, Y.J. Fu, M. Luo, D.Y. Zhang, T. Efferth, Bioresour. Technol. 101

(2010) 931.[70] K. Narasimharao, D.R. Brown, A.F. Lee, A.D. Newman, P.F. Siril, S.J. Tavener, J.

Catal. 248 (2007) 226.[71] A. Zieba, L. Matachowski, J. Gurgul, E. Bielanska, A. Drelinkiewicz, J. Mol. Catal.

A: Chem. 316 (2010) 30.[72] E. Rafiee, H. Mahdavi, M. Joshaghani, Mol. Divers 15 (2011) 125.


[73] A.A. Jafari, H. Mahmoudi, B.F. Mirjalili, J. Iranian Chem. Soc. 8 (2011) 851.[74] K.D. Parghi, J.R. Satam, R.V. Jayaram, Green Chem. Lett. Rev. 4 (2011) 143.[75] F.F. Bamoharram, M.M. Heravi, J. Ebrahimi, A. Ahmadpour, M. Zebarjad, Chin.

J. Catal. 32 (2011) 782.[76] K. Qiao, H. Hagiwara, C. Yokoyama, J. Mol. Catal. A: Chem. 246 (2006) 65.


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[77] A. Chrobok, S. Baj, W. Pudło, A. Jarzebski, Appl. Catal. A: Gen. 366 (2009) 22.[78] R. Sugimura, K. Qiao, D. Tomida, C. Yokoyama, Catal. Commun. 8 (2007) 770.[79] A.S. Amarasekara, O.S. Owereh, Catal. Commun. 11 (2010) 1072.[80] Q. Zhang, J. Luo, Y. Wei, Green Chem. 12 (2010) 2246.[81] K.B. Sihpuria, A.L. Daniel-da-Silva, T. Trindade, J.A.P. Coutinho, Green Chem.

13 (2011) 340.[82] Q. Zhang, H. Su, J. Luo, Y. Wei, Green Chem. 14 (2012) 201.[83] P. Wang, A. Kong, W. Wang, H.Y. Zhu, Y. Shan, Catal. Lett. 135 (2010) 159.[84] K. Qiao, H. Hagiwara, C. Yokoyama, J. Mol. Catal. A: Chem. 246 (2006) 65.[85] L. Han, H.-J. Choi, S.-J. Choi, B. Liu, D.-W. Park, Green Chem. 13 (2011) 1023.[86] (a) C. Fehér, E. Kriván, J. Hancsók, R. Skoda-Földes, Green Chem. 14 (2012)

403;(b) M. Baghernejad, K. Niknam, Int. J. Chem. 4 (2012) 52;(c) M.N. Sefat, D. Saberi, K. Niknam, Catal. Lett. 141 (2011) 1713;(d) H. Tajik, K. Niknam, S. Karimian, Iranian J. Catal. 3 (2013) 107;(e) K. Niknam, A. Piran, Green Sustain. Chem. 3 (2013) 1.

[87] D.W. Breck, Zeolite Molecular Sieves, John Wiley, New York, 1974.[88] J. Liu, D. Yin, D. Yin, Z. Fub, Q. Li, G. Lu, J. Mol. Catal. A: Chem. 209 (2004) 171.[89] Y. Kubota, S. Inagaki, K. Takechi, Catal. Today 226 (2014) 109.[90] A. Chica, ISRN Chem. Eng. 2013 (2013) 1.[91] N. Wijayati, H.D. Pranowo, Jumina, Triyono, Indo. J. Chem. 13 (2013) 59.[92] A. Solinas, M. Taddei, Synthesis (2007) 2409.[93] (a) B. Tamami, K.P. Borujeny, Tetrahedron Lett. 45 (2004) 715;

(b) K.P. Borujeny, B. Tamami, Catal. Commun. 8 (2007) 1191;(c) K.P. Borujeny, A.R. Massah, React. Funct. Polym. 66 (2006) 1126.

[94] (a) S. Kobayashi, S. Nagayama, J. Am. Chem. Soc. 120 (1998) 2985;(b) S. Kobayashi, I. Hachiva, J. Org. Chem. 59 (1994) 3590;(c) R. Alleti, W.S. Oh, M. Perambuduru, C.V. Ramana, V.P. Reddy, TetrahedronLett. 49 (2008) 3466.

[95] (a) A. Akela, A. Moet, Functionalized Polymers and Their Applications, 11,Wiley, New York, 1990;(b) D.C. Neckers, D.A. Kooistra, G.W. Green, J. Am. Chem. Soc. 94 (1972) 9284;(c) E.C. Blossey, L.M. Turner, D.C. Neckers, Tetrahedron Lett. 26 (1973) 1823.

[96] (a) S.-H. Lee, B.S. Lee, Bull. Korean Chem. Soc. 30 (2009) 551;(b) S. Nagayama, S. Kobayashi, Angew. Chem. Int. Ed. 39 (2000) 567;(c) H.-J. Yoon, S.-M. Lee, J.-H. Kim, H.-J. Cho, J.-W. Choi, S.-H. Lee, Y.-S. Lee,Tetrahedron Lett. 49 (2008) 3165.

[97] (a) R. Ran, D. Fu, J. Shen, Q. Wang, J. Polym. Sci. Part A: Polym. Chem. 31 (1993)2915;(b) E.C. Blossey, L.M. Turner, D.C. Neckers, J. Org. Chem. 40 (1975) 959.

[98] (a) A.P. Deshmukh, K.J. Padiya, M.M. Salunkhe, J. Chem. Res. (S) (1999) 568;(b) B. Tamami, A. Nasrolahi, K.P. Borujeni, J. Serb. Chem. Soc. 75 (2010) 423.

[99] A. Rahmatpour, J. Aalaie, Heteroatom Chem. 22 (2010) 85.100] A. Rahmatpour, J. Aalaie, Heteroatom Chem. 22 (2011) 51.101] Z. Wang, B. Gao, J. Mol. Catal. A: Chem. 330 (2010) 35.102] B. Tamami, K.P. Borujeny, Iranian Polym. J. 12 (2003) 507.103] K.V. Boroujeni, Synth. Commun. 41 (2011) 277.104] M.L. Granados, A.C. Alba-Rubio, I. Sádaba, R. Mariscal, I. Mateos-Aparicio, A.

Heras, Green Chem. 13 (2011) 3203.105] T. Okayasu, K. Saito, H. Nishide, M.T.W. Hearn, Green Chem. 12 (2010) 1981.106] R. Sugimura, K. Qiao, D. Tomida, C. Yokoyama, Catal. Commun. 8 (2007) 770.107] M.M. Lakouraj, M. Mokhtary, Monatsh Chem. 140 (2009) 53.108] S. Kobayashi, M. Sugira, H. Kitagaw, W.W.-L. Lam, Chem. Rev. 102 (2002) 2227.109] B.S. Lee, S. Mahajan, K.D. Janda, Tetrahedron 61 (2005) 3081.110] S.-H. Lee, B.S. Lee, Bull. Korean Chem. Soc. 30 (2009) 551.111] S.-H. Lee, S.T. Kadam, Appl. Organometal. Chem. 25 (2011) 608.112] A. Dutta, A.K. Patra, S. Dutta, B. Saha, A. Bhaumik, J. Mater. Chem. 22 (2012)

14094.113] S. Ahmad, M. Ali, Appl. Catal. A: Gen. 331 (2007) 149.114] S. Ahmad, M. Ali, R. Jafar, S. Ebrahim, Chem. Pharm. Bull. 55 (2007) 957.115] J.V. Madhav, Y.T. Reddy, P.N. Reddy, J. Mol. Catal. A: Chem. 304 (2009) 85.116] S. Ahmad, R. Abbas, B. Zahra, Catal. Commun. 9 (2009) 13.117] J. Safari, S.H. Banitaba, S.D. Khalili, J. Mol. Catal. A: Chem. 335 (2011) 46.118] B.V.S. Reddy, A. Venkateswarlu, Ch. Madan, A. Vinu, Tetrahedron Lett. 52

(2011) 1891.119] (a) A. Rahmatpour, React. Funct. Polym. 71 (2011) 80;

(b) H.R. Shaterian, F. Rigi, M. Arman, Chem. Sci. Trans. 1 (2012) 155–161;(c) A. Shaabani, A. Maleki, Appl. Catal. A 331 (2007) 149–151.

120] P.-L. Boey, S. Ganesan, G.P. Maniam, M. Khairuddean, S.-E. Lee, Appl. Catal. A.Gen. 433–434 (2012) 12.

121] N. Özbay, N. Oktar, N.A. Tapan, Fuel 87 (2008) 1789.122] P.K. Pääkkönen, A.O.I. Krause, Appl. Catal. A: Gen. 245 (2003) 289.123] Y. Feng, B. He, Y. Cao, J. Li, M. Liu, F. Yan, Bioresour. Technol. 101 (2010) 1518.124] C. Tagusagawa, A. Takagaki, S. Hayashi, K. Domen, J. Am. Chem. Soc. 130 (2008)

7230.125] C. Tagusagawa, A. Takagaki, K. Takanabe, K. Ebitani, S. Hayashi, K. Domen, J.

Catal. 270 (2010) 206.126] A. Takagaki, C. Tagusagawa, K. Domen, Chem. Commun. 42 (2008) 5363.127] Y.C. Li, S.R. Yan, L.P. Qian, W.M. Yang, Z.K. Xie, Q.L. Chen, B. Yue, H.Y. He, J.

Catal. 241 (2006) 173.128] K. Tanabe, S. Okazaki, Appl. Catal. A: Gen. 133 (1995) 191.


129] K. Tanabe, W.F. Holderich, Appl. Catal. A: Gen. 181 (1999) 399.130] A.S. Dias, S. Lima, D. Carriazo, V. Rives, M. Pillinger, A.A. Valente, J. Catal. 244

(2006) 230.131] X.J. Guo, W.H. Hou, W.P. Ding, Y.N. Fan, Q.J. Yan, Y. Chen, Micropor. Mesopor.

Mater 80 (2005) 269.

PRESSday xxx (2014) xxx–xxx 17

[132] I. Nowak, M. Ziolek, Chem. Rev. 99 (1999) 3603.[133] K. Tanabe, Catal. Today 78 (2003) 65.[134] C. Tagusagawa, A. Takagaki, K. Takanabe, K. Ebitani, S. Hayashi, K. Domen, J.

Phys. Chem. C 113 (2009) 17421.[135] M.A. Bizeto, A.L. Shiguiharab, V. Constantino, J. Mater. Chem. 19 (2009) 2512.[136] F.Q. Zhang, Y. Meng, D. Gu, Y. Yan, C.Z. Yu, B. Tu, D. Zhao, J. Am. Chem. Soc.

127 (2005) 13508.[137] Y. Meng, D. Gu, F.Q. Zhang, Y.F. Shi, H.F. Yang, Z. Li, C.Z. Yu, B. Tu, D. Zhao,

Angew. Chem. Int. Ed. 44 (2005) 7053.[138] Y. Meng, D. Gu, F.Q. Zhang, Y.F. Shi, L. Cheng, D. Feng, Z. Wu, Z. Chen, Y. Wan,

A. Stein, D. Zhao, Chem. Mater. 18 (2006) 4447.[139] Y. Wan, D. Zhao, Chem. Rev. 107 (2007) 2821.[140] R. Xing, N. Liu, Y.M. Liu, H.H. Wu, Y.W. Jiang, L. Chen, M.Y. He, P. Wu, Adv.

Funct. Mater. 17 (2007) 2455.[141] F. Chen, X. Meng, F.-S. Xiao, Catal. Surv. Asia 15 (2011) 37.[142] M. Kidwai, A. Jahan, J. Iranian Chem. Soc. 8 (2011) 462.[143] A.O. Barros, A.T. Faísca, E.R. Lachter, R.S.V. Nascimento, R.A.S.S. Gil, J. Braz.

Chem. Soc. 22 (2011) 359.[144] Z.-J. Yang, Y.-F. Li, Q.-B. Wua, N. Ren, Y.-H. Zhang, Z.-P. Liu, Y. Tang, J. Catal.

280 (2011) 247.[145] A.V. Narsaiah, A.R. Reddy, B.V.S. Reddy, J.S. Yadav, The Open Catal. J. 4 (2011)

43.[146] Y. Du, L. Shao, L. Luo, S. Shi, C. Qi, Turk. J. Chem. DOI:10.3906/kim-1302-70

(2014).[147] S. Sebti, R. Tahir, R. Nazih, S. Boulaajaj, Appl. Catal. A: Gen. 218 (2003) 21.[148] R. Tahir, K. Banert, A. Solhy, S. Sebti, J. Mol. Catal. A: Chem. 246 (2005) 39.[149] A. Solhy, J.H. Clark, R. Tahir, S. Sebti, M. Larzek, Green Chem. 8 (2006) 871.[150] R.V. Yarapathi, S.M. Reddy, S. Tammishetti, React. Funct. Polym. 64 (2005)

157.[151] Z. Zehui, Z.(K.) Zongbao, Chin. J. Catal. 32 (2011) 70.[152] J. Deng, L.-P. Mo, F.-Y. Zhao, L.-L. Hou, L. Yang, Z.-H. Zhang, Green Chem. 13

(2011) 2576.[153] K. Tanabe, T. Yamaguchi, Catal. Today 20 (1994) 185.[154] G.D. Yadav, J.J. Nair, Micropor. Mesopor. Mater 33 (1999) 1.[155] J.H. Clark, D.J. Nightingale, P.M. Price, G.L. Monks, J.F. White, MEL Catal. Doc-

ument (2000) 6130.[156] J.H. Clark, G.L. Monks, D.J. Nightingale, P.M. Price, J.F. White, J. Catal. 193 (2000)

348.[157] S. Wang, J.A. Guin, Chem. Commun. (2000) 2499.[158] Y. Huang, B. Zhao, Y. Xie, Appl. Catal. A: Gen. 173 (1998) 27.[159] T. Lei, J.S. Xu, Y. Tang, W.M. Hua, Z. Gao, Appl. Catal. A: Gen. 192 (2000) 181.[160] H. Matsuhashi, M. Tanaka, H. Nakamura, K. Arata, Appl. Catal. A: Gen. 201

(2001) 1.[161] J.M. Grau, C.R. Vera, J.M. Parera, Appl. Catal. A: Gen. 172 (1998) 311.[162] M.H. Al-Hazmi, A.W. Apblett, Catal. Sci. Technol. 1 (2011) 621.[163] S.A. EL-Hakam, S.M. Hassan, A.I. Ahmed, S.M. EL Dafrawy, J. Am. Sci. 7 (2011)

682.[164] Y. Liao, X. Huang, X. Liao, B. Shi, J. Mol. Catal. A: Chem. 347 (2011) 46.[165] X. Qi, H. Guo, L. Li, Ind. Eng. Chem. Res. 50 (2011) 7985.[166] A. Wang, X. Liu, Z. Su, H. Jing, Catal. Sci. Technol. 4 (2014) 71.[167] A. Sinhamahapatra, P. Pal, A. Tarafdar, H.C. Bajaj, A.B. Panda, ChemCatChem.

5 (2013) 331.[168] M. Hara, T. Yoshida, A. Takagaki, T. Takata, J.N. Kondo, S. Hayashi, K. Domen,

Angew. Chem. Int. Ed. 43 (2004) 2955.[169] M. Okamura, A. Takagaki, M. Toda, J.N. Kondo, K. Domen, T. Tatsumi, M. Hara,

S. Hayashi, Chem. Mater. 18 (2006) 3039.[170] M. Toda, A. Takagaki, M. Okamura, J.N. Kondo, S. Hayashi, K. Domen, M. Hara,

Nature 438 (2005) 178.[171] A. Takagaki, M. Toda, M. Okamura, J.N. Kodo, S. Hayashi, K. Domen, M. Hara,

Catal. Today 116 (2006) 157.[172] X. Wang, R. Liu, M.M. Waje, Z. Chen, Y. Yan, K.N. Bozhilov, P. Feng, Chem.

Mater. 19 (2007) 2395.[173] R. Xing, Y. Liu, Y. Wang, L. Chen, H. Wu, Y. Jiang, M. He, P. Wu, Micropor.

Mesopor. Mater 105 (2007) 41.[174] Y. Wang, F. Su, C.D. Wood, J.Y. Lee, X.S. Zhao, Ind. Eng. Chem. Res. 47 (2008)

2294.[175] X. Tian, F. Su, X.S. Zhao, Green Chem. 10 (2008) 951.[176] K. Nakajima, M. Okamura, J.N. Kondo, K. Domen, T. Tatsumi, S. Hayashi, M.

Hara, Chem. Mater. 21 (2009) 186, references cited therein.[177] Y. Liu, J. Chen, J. Yao, Y. Lu, L. Zhang, X. Liu, Chem. Eng. J. 148 (2009) 201,

references cited therein.[178] S. Van de Vyver, L. Peng, J. Geboers, H. Schepers, F. de Clippel, C.J. Gommes, B.

Goderis, P.A. Jacobs, B.F. Sels, Green Chem. 12 (2010) 1560.[179] X.Q. Wang, R. Liu, M.M. Waje, Z.W. Chen, Y.S. Yan, K.N. Bozhilov, P.Y. Feng,

Chem. Mater 19 (2007) 2395.[180] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V.

Grigorieva, A.A. Firsov, Science 306 (2004) 666.[181] M.J. Allen, V.C. Tung, R.B. Kaner, Chem. Rev. 110 (2010) 132.[182] J. Ji, G. Zhang, H. Chen, S. Wang, G. Zhang, F. Zhang, X. Fan, Chem. Sci. 2 (2010)

484.[183] H.I. Ryoo, L.Y. Hong, S.H. Jung, D.-P. Kim, J. Mater. Chem. 20 (2010) 6419.


[184] P. Lin, B. Li, J. Li, H. Wang, X. Bian, X. Wang, Catal. Lett. 141 (2011) 459.[185] M. Kitano, K. Arai, A. Kodama, T. Kousaka, K. Nakajima, S. Hayashi, M. Hara,

Catal. Lett. 131 (2009) 242.[186] X. Liang, C. Li, C. Qi, J. Mater. Sci. 46 (2011) 5345.[187] Q. Xu, Z. Yang, D. Yin, J. Wang, Front. Chem. Eng. China 3 (2009) 201.


























































































































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8 P. Gupta, S. Paul / Cataly

[188] G. Chen, B. Fang, Bioresour. Technol. 102 (2011) 2635.[189] F. Lin, Z. Kun, L. Xiaohong, W. Haihong, W. Peng, Chin. J. Catal. 33 (2012) 114.[190] (a) P. Gupta, S. Paul, Green Chem. 13 (2011) 2365;

(b) P. Gupta, S. Paul, Curr. Catal. 3 (2014) 53;(c) P. Gupta, S. Paul, J. Mol. Catal. A: Chem. 352 (2012) 75;(d) P. Gupta, M. Kour, S. Paul, J.H. Clark, RSC Adv. 4 (2014) 7461.

[191] F. Liang, Y. Song, C. Huang, J. Zhang, B. Chen, Catal. Commun. 40 (2013) 93.[192] F.-l. Pua, Z. Fang, S. Zakaria, F. Guo, C.-h. Chia, Biotechnol. Biofuels 4 (2011)

56.[193] H. Alinezhad, M. Zare, J. Chil. Chem. Soc. 58 (3) (2013) 1840.[194] H. Guo, Y. Lian, L. Yan, X. Qi, R.L. Smith Jr., Green Chem. 15 (2013) 2167.[195] B.M. Rao, G.N. Reddy, T.V. Reddy, B.L.A.P. Devi, R.B.N. Prasad, J.S. Yadav, B.V.S.

Reddy, Tetrahedron Lett. 54 (2013) 2466.[196] K.N. Gangadhar, M. Vijay, R.B.N. Prasad, B.L.A.P. Devi, Green Sustain. Chem. 3


(2013) 122.[197] W.-Y. Lou, Q. Guo, W.-J. Chen, M.-H. Zong, H. Wu, T.J. Smith, Chem. Sustain.

Chem. 5 (2012) 1533.[198] F.-C. Zheng, Q.-W. Chen, L. Hu, N. Yana, X.-K. Konga, Dalton Trans. 43 (2014)

1220.

PRESSday xxx (2014) xxx–xxx

[199] W.-J. Liu, K. Tian, H. Jiang, H.-Q. Yu, Sci. Rep. 3 (2013) 1, Article number: 2419.[200] K. Nakajima, M. Hara, ACS Catal. 2 (2012) 1296.[201] M. Hara, Energy Environ. Sci. 3 (2010) 601.[202] J. Macht, R.T. Carr, E. Iglesia, J. Catal. 264 (2009) 54.[203] C. Reddy, V. Reddy, R. Oshel, J.G. Verkade, Energy Fuels 20 (2006) 1310.[204] C.M. Garcia, S. Teixeira, L.L. Marciniuk, U. Schuchardt, Bioresourc. Technol. 99

(2008) 6608.[205] (a) Dutch National Research School Combination Catalysis Controlled by

Chemical Design, Future perspectives in catalysis. (NRSC-Catalysis), Eind-hoven (Netherlands) April 2009;(b) S. Mitchell, N.-L. Michels, G. Majano, J. Pérez-Ramírez, Curr. Opin. Chem.Eng. 2 (2013) 304;(c) A. Holewinski, H. Xin, E. Nikolla, S. Linic, Curr. Opin. Chem. Eng. 2 (2013)312;


(c) L.F. Gladden, Curr. Opin. Chem. Eng. 2 (2013) 331;(d) N. Al-Rifai, E. Cao, V. Dua, A. Gavriilidis, Curr. Opin. Chem. Eng. 2 (2013)338.

[206] V. Dal Santo, F. Liguori, C. Pirovano, M. Guidotti, Molecules 15 (2010)3829.



























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Solid acids: Green alternatives for acid catalysis

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