CHEMISTRY UPPER 6ORGANIC CHEMISTRY

CHAPTER 7 : CARBOXYLIC ACID& ITS DERIVATIVES

7.1 Nomenclature

� Organic acid containing one or more carboxyl (COOH) groups as functioning group

� Carboxylic acid has the general formula of CnH2n+1COOH or sometimes CnH2nO2.

� The naming of carboxylic acid end with –oic acid.

NameMethanoic

acid

Ethanoic

acid

Propanoic

acid

Butanoic

acid

Pentanoic

acid

Hexanoic

acid

7.1.1 Naming carboxylic acid

1. Find the longest chain that attached to –COOH and name them accordingly. The C in COOH is C1.

2. Identify the group that attached to the parent chain and name them accordingly

3. Give the numbering of the group that attached accordingly

Structure HCOOH CH3COOH C2H5COOH C3H7COOH C4H9COOH C5H11COOH

2-methylbutanoic acid6-chloro-

4,4-dimethylhexanoic

acid

2-ethyl-3-

methylpentanoic acid

3-hydroxy-3-

methylpentanoic acid

3-methylbutanoic

acid

3-ethyl-3-

methylpentanoic

acid

2,3,4-

trimetylpentanoic

acid

Pentandioic acid

3,5-dibromobenzoic acid 2-phenylbutanoic acidPropanedioic acid

or malonic acid

But-2-enedioic acid

CH2CCH2COOH

CH3

CH2CH3

H3C CH3CHCHCHCOOH

CH3

CH3

CH3HOOCCH2CH2CH2COOH

� Practice : Draw all isomers for carboxylic acid with formula C3H7COOH

CH3CH2CH2C

O

OH

6.2 Physical properties

(A) Boiling point – The trend of the boiling points of may be caused by many factors

a) Factors of the number of carbon atom

HCOOH CH3COOH C2H5COOH C3H7COOH

Explanation :

Boiling point increase

When going down to homologous series, the boiling point increase. This is due to the increase in relative molecular mass, which increase the weak Van Der Waals forces causing boiling point increase.increase the weak Van Der Waals forces causing boiling point increase.

Boiling point of different functioning group

Compoundpropanol

(C3H7OH)CH3COOH Butane (C4H10)

Chloroethane

(C2H5Cl)

RMM 60 60 58 64.5

Boiling

point (oC)78 117 4.4 21

point ( C)

Explanation : Ethanoic acid has the highest boiling point among these organic compound as it form dimer among itself using 2 hydrogen bonds. Propanolwhich has same molecular mass, contain only 1 hydrogen bond, has a lower boiling point. Chloroethane has higher boiling point compare to butane as it is a polar molecules which form permanent dipole while butane is a non-polar molecules which form induced dipole.

� Solubility of Carboxylic Acid

HCOOH CH3COOH C2H5COOH C3H7COOH C4H9COOH

Solubility decrease

Explanation :methanoic, ethanoic and propanoic acid are completely miscible in water as they can form hydrogen bond with water. However, the LONGER the water as they can form hydrogen bond with water. However, the LONGER the ALKYL GROUPS ATTACHED, molecule become MORE HYDROPHOBIC. As a result, HYDROGEN BOND BECOME LESS SIGNIFICANT and cause the solubility decrease.

(C) Acidity of carboxylic acid

� Carboxylic acid is considerably weak acid since it has a small pKa

value. It undergoes partial dissociation

aaa KpKRCOOH

OHRCOOK lg

][

]][[ 3−==

+−

Name Methanoic acid Ethanoic acid Propanoic acid

Structure HCOOH CH3COOH C2H5COOH

pKa 3.75 4.76 4.90

Name Benzoic acid 2-chloro-ethanoic acid 2-methyl ethanoic acid

Structure C6H5COOH CH2(Cl)COOH CH2(CH3) COOH

pKa 4.19 4.42 4.86

� Carboxylic acid is generally a stronger weak acid than alcohol, since the charge delocatisation at carboxylate ion makes the ion formed become more stable as it formed resonance structure due to mesomeric effect, hence increase the stability of carboxylate ionwhich result the equilibrium favour to right position (favour to position of donate proton)position of donate proton)

� Similar to alcohol, carboxylic attached to an alkyl has lower acidity compare to carboxylic acid attached to a phenyl. This is due to alkyl is an electron donating group, while a phenyl is an electron withdrawing group

Carboxylic acid Explanation

Carboxylic acid dissociate in water according to the equation

R-COOH + H2O R-COO- + H3O+

Alkyl group, which is an electron donating group, donate electron to O

and caused the electron density of O in R–OH increase. As a result, O is

more readily to accept proton.

Acidity decrease in the order, where

Methanoic acid > Ethanoic acid > Propanoic acid

This is due to, longer the alkyl chain, stronger the electron donating

effect, equilibrium favours more to left.

Benzoic acid

Benzoic acid dissociate in water according to the equation

C6H5–COOH + H2O C6H5–COO- + H3O+

The phenyl group is an electron-withdrawing group, which withdrawn the

electron density from partially negative charge, δ−, from O making O

less readily to accept proton. As a result, O is more readily to donate

proton which makes equilibrium favour more to right.

p-methylbenzoic acid

Since CH3 is an electron donating group to benzene ring, it will increase

the electron density in benzene ring, hence increase the polarity of -O-H

bond in the benzene ring. As a result, H is harder to dissociate, hence

caused the equilibrium to shift slightly to the left, decreasing the acidity

of benzoic acid

Effect of the distance

of electron

withdrawing group

toward acidity of

butanoic acid

Due to inductive effects operate through π bonds and are dependent on distance, the

effect of halogen substitution decreases as the substituent moves farther from the

carboxyl. Thus, 2-chlorobutanoic acid has pKa = 2.86, 3-chlorobutanoic acid has pKa =

4.05, and 4-chlorobutanoic acid has pKa = 4.52.

Effect of the number

of substituent toward

acidity of ethanoic

acid

-Cl act as electron withdrawing group in carboxylic acid. Note that as the number of -Cl

increased, the acidity increased. This can be explained in term of the increment of

negative inductive effect caused by -Cl, which further stabilise the conjugate base

formed. As a result, equilibrium shift to right, increased the acidity.

7.3 Chemical Properties of Carboxylic acid

7.3.1 Preparation of carboxylic acid

Name of

reaction

Reagent used

and conditionEquation

Oxidation of

10 alcohol

Acidified KMnO4

or acidified

K2Cr2O7 + heat Propan-1-ol propanoic acid

Oxidation of Acidified KMnO4

or acidified aldehyde

or acidified

K2Cr2O7 + heat Propanal propanoic acid

Hydrolysis of

nitrile

Dilute sulphuric

acid H2SO4 +

H2O under reflux2-methylbutylnitrile 2-methylbutanoic acid

Hydrolysis of

ester

Dilute HCl /

NaOH with heat

Name of

reaction

Reagent

used and

condition

Equation

Properties

of an acid

Alkali,

NaOH or

Na2O

7.3.2 Chemical reaction of carboxylic acid

of an acid

-----------

Reaction

with alkali,

metal and

metal

carbonate

Sodium, Na

Sodium

carbonate,

Na2CO3

Name of

reaction

Reagent used

and conditionEquation

Esterification

Alcohol

catalysed by

concentrated

sulphuric acid

Formation of

acyl chloride

Phosphorous

pentachloride(P

Cl5)

@acyl chloride @

Thionyl chloride

(SOCl2)

Reduction –

Formation of

alcohol

Lithium

aluminium

hydride ;

LiAlH4 with dry

ether

(1) Reaction of acid-base : Formation of salts

A. Reaction with base (metal hydroxide and metal oxide)

� Like all acid, when carboxylic acid reacts with base, it will form salt and water

Carboxylic Acid Base Salt Water

CH3COOH NaOH

CH CH COOH K O

CH3COO–Na+ H2O

CH3CH2COO–K+ H OCH3CH2COOH K2O

CH3CH2CH2COOH Mg(OH)2

CH3CH2COO–K+ H2O

Mg(CH3CH2CH2COO)2 H2O

B. Reaction with metal

� When acid react with metal, a colourless gas liberated. This gas will give “pop” sound when burning splinter is put close to the gas liberated, indicating ………… gas is released.

Carboxylic Acid Metal SaltHydroge

n

CH3COOH Zn Zn(CH3COO)2 H2

hydrogen

CH3CH2COOH Mg Mg(CH3CH2COO)2 H2

C. Reaction with metal carbonate

� When acid react with metal carbonate solution, an effervescence is observed and a colourless released and gas turned lime water chalky, indicating ………..……… gas is released.

Carboxylic Acid Metal carbonate SaltCarbon

Water

carbon dioxide

Carboxylic Acid Metal carbonate SaltCarbon

dioxideWater

CH3CH(CH3)COOH K2CO3

CH3CH2COOH ZnCO3

CO2 H2O

Zn(CH3CH2COO)2

CH(CH3)2COO–K+

CO2 H2O

(2) Esterification – Formation of ester

� When alcohol reacts with carboxylic acid catalysed by concentrated sulphuric acid, ester and water is formed. The –H is donated by alcohol while –OH is given off by carboxylic acid

carboxylic acid alcohol ester

Carboxylic Acid

Carboxylate ion

Alcohol

Alkyl

Name of ester :

Alkyl carboxylate

Carboxylic Acid Alcohol Ester Water

CH3COOH CH3CH2OH

CH3CH(CH3)COOH CH3CH2CH2OH

H2O

H2O

CH3C(CH3)2COOH CH3CH(CH3)OH H2O

H2O

(3)Formation of acyl chloride

� When carboxylic acid is reacted with a chlorine-rich compound such as phosphorous pentachloride (PCl5) or thionyl chloride (SOCl­2), an acylchloride is formed. A white fume of hydrogen chloride is given off as side product.

� The reaction take place is a nucleophilic substitution reaction.

Carboxylic acidChlorine

CompoundAcyl chloride

Side

product

Hydrogen

chloride

CH3CH2COOH PCl5

CH3CH(CH3)COOH SOCl2

CH3CH(CH3)CH2COOH HCl

PCl5

CH3CH2COCl + POCl3 + HCl

CH3CH(CH3)COCl + SO2 + HCl

CH3CH(CH3)CH2COCl + H2O

+ POCl3 + HCl

(4) Reduction of carboxylic acid : Formation of alcohol

� Using strong reducing agent such as lithium tetrahydridoluminate(LiAlH4), carboxylic acid is readily to reduce to become alcohol.

� Reagent : Lithium tetrahydridoaluminate (LiAlH4) under dry ether

CH3CH2COOH + LiAlH4

CH3CH(CH3)COOH + LiAlH4

→etherdry

→etherdry

CH3CH2CH2OH + H2O

CH3CH(CH3)CH2OH + H2O

CH3C(CH3)2COOH + LiAlH4

+ LiAlH4

→etherdry

C(CH3)3CH2OH + H2O

→etherdry

7.3.3 Simple test for carboxylic acidDifferentiate Chemical test Observation & Equation

Carboxylic

acid with

other

Sodium

carbonate,

Na2CO3

Positive test : Carboxylic acid

Effervescence occurs. Gas released turn lime

water chalky indicating carbon dioxide is released.

Eq. : R–COOH + Na2CO3 �

R–COO-Na+ + CO2 + H2O

Positive test : Carboxylic acid

Dark red solution is obtained when FeCl3 is added

to carboxylic acid. other

organic

compound Iron (III)

chloride, FeCl3

to carboxylic acid.

Equation :

CH3COO- + FeCl3 � Fe(CH3COO)3 + 3 Cl-

red solution

When boiled, the red solution turns to brown

precipitate.

Fe(CH3COO)3 + 2 H2O �

Fe(CH3COO)(OH)2 + 2 CH3COOH

brown precipitate

7.4 Methanoic acid (Common name : formic acid)

� Methanoic acid is the first member of carboxylic acid homologous series. Not only it shows the similar properties of carboxylic acid as proposed earlier, it also possessed other special properties.

� This special properties is due to the of having 2 functioning group at the same molecule where

Functioning Functioning as

as aldehyde carboxylic acid

� Methanoic acid is a strong reducing agent, unlike other carboxylic acid. It is easily oxidised to form carbon dioxide as shown in the following reaction (can also be its salt like HCOONa)

Reaction with Observation, Equation and explanation

Silver nitrate,

AgNO3

Observation : White precipitate is 1st formed and eventually

turn to silver

Equation : HCOONa + AgNO3 �

HCOOAg (white ppt) + NaNO3

2 HCOOAg � 2 Ag (silver) + CO2

Tollen’s Test

Due to the presence of aldehyde as functioning group, it give

positive test to

Tollen reagent (silver complex)

Observation : a silver mirror is observedTollen’s Test

Observation : a silver mirror is observed

Equation : HCOOH + Ag2O �

2 Ag (silver mirror) + CO2 + H2O

Mercury (II)

chloride,

HgCl2

Methanoic acid reduce mercury (II) chloride to mercury (I)

chloride (white ppt)

Equation : HCOOH + 2 HgCl2 � Hg2Cl2 + CO2 + 2 HCl

Under excess methanoic acid, a black precipitate of mercury

is observed

Equation : HCOOH + Hg2Cl2 � CO2 + 2 HCl + 2 Hg

Reaction with Observation, Equation and explanation

Dehydration :

reaction with

conc.

sulphuric

acid, H2SO4

When heated with conc. H2SO4, methanoic acid dehydrated

and produce carbon monoxide and water

Equation : HCOOH CO + H2O

Acidified

potassium

As discussed earlier, when methanoic acid dissolved in

KMnO4 / H+, the purple colour of potassium manganate (VII) is

→ 42SOH.conc

potassium

manganate

(VII).

KMnO4 / H+

KMnO4 / H+, the purple colour of potassium manganate (VII) is

decolourised while carbon dioxide and water is formed

Equation : HCOOH + KMnO4 / H+ � CO2 + H2O

Phosphorous

pentachloride

, PCl5

Unlike other carboxylic acid, when react with phosphorous

pentachloride, it will not form acyl chloride

Equation : HCOOH + PCl5 � CO + 2 HCl + POCl3

7.5 Ethanedioic acid, H2C2O4 (also known as oxalic acid)

� The structure of ethanedioic acid can be described as

� It dissolve in alcohol and water but not in organic solvent such as propanone or ether.

� It can be prepare by the following method :

Step 1 : heating sodium methanoate Step 2 : add with sulphuric acid

2 HCOONa Na C O + HNa2C2O4 + H2SO4→

∆

→∆2 HCOONa Na2C2O4 + H2

Na2C2O4 + H2SO4

H2C2O4 + Na2SO4

→∆

→∆

� Reaction with ethanedioic acid

Reaction with Observation, Equation and explanation

Acidified

potassium

manganate (VII),

KMnO4 / H+

The purple colour of potassium manganate (VII) is reduced to Mn2+

which is pink colour according to the equation

Equation : 5 C2O42- + 2 MnO4

- + 16 H+ � 2 Mn2+ + 8 H2O +

10 CO2

Concentrated

sulphuric acid,

H2SO4

Similar to methanoic acid, dehydration occur when added to conc.

H2SO4

Equation : H2C2O4 + conc. H2SO4 � CO2 + CO + H2O

Calcium chloride,

CaCl2

White precipitate is observed when reacted

Equation : Ca2+ + C2O42- � CaC2O4 (white precipitate)

7.6 Uses of Caboxylic acid

� Methanoic acid and ethanoic acid is used in rubber industries to coagulate latex

� Ethanoic acid is used as preservative and additive in food industries

� Ethanoic acid is used to manufacture ethanoic anhydride

Ethanoic anhydride is used to manufacture aspirin

� Benzoic acid is used as preservative. It is also used as an antibacterial and antifungal agent

� Calcium propanoate (react propanoic with calcium hydroxide) is used as preservative in bread to prevent the growth of mold

� Dicarboxylic acid is used mainly in manufacturing synthetic polymer such as nylon

7.7 Carboxylic Acid’s Derivatives

� In this Chapter, we’re looking into organic compounds derived from carboxylic acid. Examples of these compounds are

→acyl chlorides → esters → amides

7.7.1 Physical properties of carboxylic acid derivatives

� The boiling point of a few organic compounds are shown below

Name Molecular structure Molecular mass Boil point (0C)

Ethanoyl chloride CH-3COCl 78 51

Ethyl methanoate CH3COOCH3 74 57

Butanal CH CH CH COH 72 76Butanal CH3CH2CH2COH 72 76

Butanone CH3COCH2CH3 72 80

Propanamide CH3CH2CONH2 73 213

Propanamide has the highest boiling point among these organic compound as it contain 2 hydrogen bonds. Butanal and butanone are polar molecule which are held by permanent dipole – permanent dipole, while ethanoyl chloride and ethyl methanoate is non-polar which are held by temporary dipole – induced dipole.

7.8 Acyl chloride

� Acyl chloride has the general formula of CnH2n+1COCl.

� The ending of alkyl group attached to COCl = ~noyl chloride

� Acyl chlorides are colourless liquids with pungent smell. They are very reactive compound

� CH3COCl

� CH3CH2COCl

� CH3CH(CH3)COCl

C H COCl

Ethanoyl chloride

Propanoyl chloride

2-methylpropanoyl chloride

Benzoyl chloride� C6H5COCl

7.8.1 Chemical properties of acyl chlorides

� Most of the reaction of acyl chlorides are acylation reaction, where the –Clis substitute out easily.

� This is due to the negative inductive effect (–I) of the oxygen atom, which cause the carbon atom become more positively partial charged. As a result, C–Cl carries a much higher partially positive charge and become more reactive for nucleophilic attack

Benzoyl chloride

Name of

reaction

Reagent

used and

condition

Equation

Hydrolysis Water

propanoyl chloride water propanoic acid

Esterification Alcoholpropanoyl chloride ethanol

ethyl propanoate

Formation of

amide

Ammonia of

amine

propanoyl chloride ammonia propylamide

(A) Hydrolysis of acyl chloride

� Acyl chloride undergoes hydrolysis when react with water to form carboxylic acid. A white fume of hydrogen chloride is released as side product of the reaction.

� Hydrolysis occur vigorously as the –Cl is readily to leave the group. Examples of reaction

Acyl chloride Water Carboxylic acid HCl

CH COCl + H O HClCH COOHCH3COCl + H2O HCl

CH3CH(CH3)COCl + H2O HCl

+ H2O HCl

CH3COOH

CH3CH(CH3)COOH

(B)Formation of ester

� Acyl choride react with alcohol / phenol at room temperature to form ester. Unlike carboxylic acid, which required an acidic medium, acyl chloride does not require an acidic medium.

� Similar to the hydrolysis of acyl chloride, a white fume of hydrogen chloride is released.

Acyl chloride Alcohol Ester HCl

CH3COCl CH3CH2OH HClCH3COOCH2CH3

� When phenol react with benzoyl chloride, NaOH is used.

CH3CH2CH2COCl CH3CH2CH2OH HCl

CH3C(CH3)2COCl CH3OH HCl

CH3CH2CH2COOCH2CH2CH3

CH3C(CH3)2COOCH3

HCl

(C) Formation of amide

� Acyl chloride form amides when reacted with ammonia, primary and secondary amine

Acyl chlorideAmmonia /

amineAmide HCl

CH3CH2COCl NH3 HClCH3CH2CONH2

CH3COCl CH3CH2NH2 HCl

CH3CH2CH2COCl CH3NH(CH3) HCl

CH3CONHCH2CH3

CH3CH2CH2CON(CH3)2

7.9 Ester

� Esters are the functional isomerism of carboxylic acid. Similar to carboxylic acid, it has the general formula of CnH2nO2. In naming ester, the alkyl attached to alcohol is named where the carboxylic acid is named as its anion. Examples

Methyl propanoate

Ethyl butanoate

� Lower esters are colourless liquid with pleasant fruity odour. Larger esters are colourless solid.

� Small ester such as methyl methanoate or ethyl methanoate is soluble in water. Most of the esters are insoluble in water but soluble in organic solvent.

Propyl benzoate

Phenyl benzoate

7.9.1 Preparation of ester

Name of

reaction

Reagent used

and conditionEquation

Esterification

by

carboxylic

acid with

alcohol

Alcohol

catalysed by

concentrated

sulphuric acid

Esterification

by acyl

chloride with

alcohol

Alcoholpropanoyl chloride ethanol

ethyl propanoate

7.9.2 Chemical reaction of ester

Name of

reaction

Reagent used

and conditionEquation

Hydrolysis

Diluted acidic

solution

Hydrolysis

of ester

Sodium

hydroxide

(NaOH)

Name of

reaction

Reagent used

and conditionEquation

Reaction

with

ammonia

Concentrated

NH3

ethyl propanoate ammonia

propylamide ethanol

Reduction

of ester

Lithium

tetrahydrido-

aluminate

(LiAlH4)

ethyl propanoate

propan-1-ol ethanol

(A) Hydrolysis of ester

� Hydrolysis of ester is a reverse reaction of esterification. When ester is dissolved in diluted acidic solution, it will form back carboxylic acid and ester.

Ester Water Carboxylic acid Alcohol

+ H2O/

H+

CH3CH2CH2COOH

CH3CH2CH2OH

+ H2O/

H+

+ H2O/

H+

CH3CH(CH3)CH2COOH

CH3CH2CH2OH

CH3CH2COOH

CH3CH(OH)CH3

� When ester is hydrolysed under alkaline condition, metal salt is formed together with alcohol

� Example ; when ethyl propanoate is hydrolysed under alkaline condition.

� When sodium propanoate is react using acid such as sulphuric acid, the carboxylic acid formed back.the carboxylic acid formed back.

(B)Formation of amide : reaction with ammonia

� Ammonia is a weaker nucleophile compare to hydroxide ion. So, to effectively react with ester, concentrated ammonia is mixed with ester and heated. The products are an amide and alcohol

Ester Ammonia Amide Alcohol

+ NH3 CH3CH2CONH2CH3CH2OH

+ NH3

+ NH3

CH3OH

CH3CH2CONH2

(C) Reduction of ester

� When reduced using strong reducing agent such as LiAlH4, ester will formed alcohol as products

Ester LiAlH4 Alcohol Alcohol

LiAlH4 /

H+ CH3CH2CH2OH CH3CH2OH

LiAlH4 /

H+

LiAlH4 /

H+

CH2OH CH3OH

CH3CH2CH2OH

7.9.3 Natural ester (Lipid) – Fats and Oils

� Lipids are organic substance found in living organisms, which is insoluble in water.

� Members of lipid include fats and oils, steroids, waxes and some vitamins.

� Fatty acids are common name for long-chain carboxylic acid obtained from fats and oils

� They are natural esters formed from propan-1,2,3-triol (known as glycerol) and long chain fatty acid.

+ 3 CH3(CH2)14COOH

� There are 2 types of fatty acid which are known as saturated fatty acid and unsaturated fatty acid.

� Saturated fatty acid – all C–C are singly bonded to each other in the long carbon chain

� Unsaturated fatty acid – contain at least 1 C=C within the long carbon chain. If there’s only one C=C in the long carbon chain, it is known as monounsaturated fat. If there’s more than one C=C, they are known as polyunsaturated fat.

� In natural product of fats and oils contain mixture of saturated fatty acid and unsaturated fatty acid

Polyunsaturated Monounsaturated Fats / oil Saturated fat

Polyunsaturated

fat

Monounsaturated

fat

Palm oil 51% 10% 39%

Sunflower oil 11% 69% 20%

Olive oil 14% 9% 77%

Butter fat 66% 4% 30%

Lard 41% 12% 47%

Manufacture of soap

� An important use of soap is in soap making. Soaps are sodium (Na) or potassium (K) salts of long chain of fatty acids. Hydrolysis of fats / oils in aqueous NaOH ( known as saponification) form glycerol& sodium carboxylatesalt (soap).

� The cleansing action of soap is due to the hydrophobic part of soap which dissolves in grease easily and dirt are removed easily using the attraction forces between cation and the negative head of soap.

Application of ester in industries

� Used as food additive in food processing industries (taste enhancer, flavouring � Used as food additive in food processing industries (taste enhancer, flavouring and preservatives)

� Solvent for drugs, antibiotics and cosmetic.

� Use to produce cosmetic, perfume / cologne and air-freshener.

� Polystyrene cement – use to bind to another type of surface in the cement

� Polyester (terylene) – synthetic fibres in textiles industries.

� Polystyrene (alkyd resin) – used in pain and surface coating

� Unsaturated polyester are readily copolymerised to give thermosetting products. They are used in the manufacture of glass fiber products for reinforcement in boat and cars.

7.10 Amides

� Amides are organic compound with the general formula of CnH2n+1CONH2. Amides are formed by replacing hydroxyl (–OH) with amine (–NH2) group.

� Naming of amide end with suffix “amide”. Examples of amides are

ethanamide

propanamidepropanamide

butanamide

benzamide

20 amide

30 amide

N-propylethanamide

N-phenylpropanamide

30 amide

N-ethyl-N-methylbutanamide

N,N-dimethylbenzamide

7.11 Preparation of amide

Name of

reaction

Reagent

used and

condition

Equation

Reaction

with amine

Acyl chloride

with

ammoniapropanoyl chloride ammonia propylamide

Acyl chloride

with amineEthanoyl chloride propylamine

Heating

ammonium

salt with

ester

Ammonium

salt with

ester

ammonia ethanamide

Name of

reaction

Reagent used

and conditionEquation

Hydrolysis

of amide

Diluted HCl

under reflux ethanamide ethanoic acid

Dehydration

of amide

Distilled over

phosphorous

pentoxide,

P2O5 Propanamide propanitrile

Reaction

with nitrous

acid, HNO2

Nitrous acid,

HNO2

Propanamide nitrous acid

propanoic acid

Name of

reaction

Reagent

used and

condition

Equation

Hoffmann

degradation

Bromine in

sodium

hydroxide,

NaOH

propanamide

ethylamine

Reduction

of amide

Lithium

tetrahydrido-

aluminate,

LiAlH4

propanamide

propylamine

(A) Hydrolysis of amide

� Amide slowly hydrolysed by refluxing with dilute acid / alkali solution. In both cases, the intermediate product is ammonium salt of carboxylic acid

Step 1 : Formation of ammonium salt

Step 2 : Formation of carboxylic acid

Under acidic

medium

Step 2 : Formation of carboxylic acid

Overall :

Under alkaline

medium

(way of

Step 1 : Formation of ammonium salt

Step 2 : Formation of carboxylate salt

(way of

distinguish

between amine

and amide)Overall :

(B)Dehydration of amide

� When amides are distilled over P2O5, phosphorous pentoxide, nitriles are formed. So P2O5 act as dehydrating agent. The H2 from NH2 and O from C=O are withdrawn out and formed water.

� The nitrile formed can be later used to synthesis amine and carboxylic acid using suitable reagent

Amide Reagent Nitrile Reagent Compound

→ 52OP → 4LiAlH→ 52OP → 4LiAlH

→ 52OP →+H,OH2

→ 52OP → 4LiAlH

(C) Reaction with nitrous acid, HNO2

� Nitrous acid, HNO2, can be prepared by treating sodium nitrite, NaNO2, with dilute HCl in cold

NaNO2 (aq) + HCl (aq) HNO2 + NaCl

� When nitrous acid, HNO2, react with amide, carboxylic acid, nitrogen and water is produced

→cold

Amide Nitrous acid Carboxylic acid Side product

+ H2OHNO2

HNO2

HNO2

+ H2O+ N2

+ H2O+ N2

+ H2O+ N2

(D) Hoffmann Degradation : Way of shortening chain.

� The terms degradation mean reduce the number of carbon, an opposite of forming nitrile to increase no of carbon in an organic compound.

� The reagents used for Hoffmann degradation are bromine solution in sodium hydroxide (Br2 in NaOH)

Amide

Bromine in

sodium

hydroxide

Amine Side products

hydroxide

Br2 + 4 NaOH

Br2 + 4 NaOH

Br2 + 4 NaOH

CH3CH2NH2

+ Na2CO3

+ 2 NaBr+ 2 H2O

CH3CH2CH2NH2

+ Na2CO3

+ 2 NaBr+ 2 H2O

+ Na2CO3

+ 2 NaBr+ 2 H2O

(E)Reduction of amide

� Amide can be reduced to become an amine using strong reducing agent such as LiAlH4 (lithium tetrahydridoaluminate) under dry ether. The number of carbon after reduction remains the same

AmideStrong reducing

agentAmine

Side

products

LiAlH4 CH3CH2CH2NH2 + H2O

LiAlH4

LiAlH4

3 2 2 2 2

CH3CH2CH2CH2NH2 + H2O

+ H2O

RCOOH + H2O � RCOO- + H3O+

Acidity increase from CH3COOH < CH2ClCOOH < CHCl2COOH

Cl is electorn withdrawing group / caused negative inductive effect / Greater

number of Cl will increase the inductive effect, causing more acidic [1]

[H3O+] = pH = 1.9100.00014.0][ 3 ×=×

+OHorcKa

pKa = - lg Ka ; pKa = 1.3

alkene / C=C

hydroxyl group / -OHhydroxyl group / -OH

Aldehyde / -CHO

O CH2

CCO- CH2 OH

KMnO4 / H+ cold , dilute

oxidation

Chlorine gas under UV

NaOH reflux

C C

H

OH

H

HO

X

Effervescences occur, which turn lime water chalkyEffervescences occur, which turn lime water chalky

CH3COOH + NaHCO3 � CH3COO-Na+ + H2O + CO3

Y

Silver mirror is observed

CH2(OH)CHO + 2Ag+ + 3OH-� CH2(OH)COO- + 2H2O + 2 Ag

Acidic trend increase from 1 < 2 < 3 [1]

This is due to, when number of Cl increase, the negative inductive effect

increase gradually[1], which increase the acidityincrease gradually[1], which increase the acidity

Acid 2 is stronger than Acid 4 [1]

This is due to, inductive effect is stronger if Cl is closer to the π-bond of

COOH group [1]

[H3O+] =

pH = 3.5010.01026.1][ 5

3 ××=×−+

OHorcK a

ester

Dilute HCl under reflux

CH3OH catalysed by H2SO4 under reflux

CH2(Br)CH(Br)CH2(Br)

COOHCOCOOH

890g of triglyceride produces 3 × 298 = 894 g of biodiesel [1]

∴ 500kg produces 500 × 894/890 = 502 kg biodiesel [1]

C17H35CO2CH3 + 27 ½ O2 → 19 CO2 + 19 H2O

Mass of CO produced = 10 × 44 × 19/298 Mass of CO2 produced = 10 × 44 × 19/298

= 28 kg.

• economic argument (NOT just “cheaper”) – e.g. oil will become increasingly more

expensive as it runs out

• ref to CO2 cycle (e.g. no net increase in CO2, i.e. “carbon neutral”) or less global

warming (due to a smaller carbon “footprint”)

• renewable/sustainable

• the effect of biofuel cultivation on world food prices