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CHEMISTRY –CLASS XII

UNIT XII-ALDEHYDES, KETONES AND CARBOXYLIC ACIDS

PART-III

[Carboxylic acids: Nomenclature, preparation , physical properties, chemical properties and uses ]

PREPARED BY

K C HUBBALLI,

PGT CHEMISTRY

JNV UTTARA KANNADA

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Outline

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CARBOXYLIC ACIDS

Review of previous session

What are carboxylic acids?

Nomenclature of carboxylic acids

Structure of the carboxyl group

Methods of preparation of carboxylic acids

Physical properties of carboxylic acids

Chemical properties of carboxylic acids

Uses of carboxylic acids

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Review of the previous session

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  • Let us recall the important reactions of aldehydes and ketones such as
  • nucleophilic addition reactions,
  • reduction,
  • oxidation,
  • Aldol and cross aldol condensation,
  • Canizzaro reaction etc.
  • Also we have covered the important uses of aldehydes and ketones
  • In this session we are discussing about another class of carbonyl compounds, carboxylic acids, most of which are naturally occurring carbon compounds

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What are carboxylic acids?

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Carbon compounds containing a carboxyl functional group –COOH are called carboxylic acids

In carboxylic acids the carbonyl carbon is bonded to oxygen atom of hydroxyl group

Higher members are also called as fatty acids, occur in natural fats and oils as esters of glycerol.

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Nomenclature of carboxylic acids

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Common names of carboxylic acid are obtained from the Latin or Greek names of their natural sources

IUPAC names of carboxylic acids are given by replacing ending ‘e’ of the corresponding alkane by suffix ‘oic acid’

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Nomenclature of carboxylic acids……..

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Structure of the carboxyl group

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Methods of preparation of carboxylic acids

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1. From primary alcohols and aldehydes

2. From alkyl benzenes

3. From nitriles and amides

4. From Grignard reagent

5. From acyl halides and anhydrides

6. From esters

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Methods of preparation of carboxylic acids……

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  1. From primary alcohols

and aldehydes

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Methods of preparation of carboxylic acids……

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2. From alkyl benzenes

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Methods of preparation of carboxylic acids……

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3.a) From

nitriles

b) From

amides

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Methods of preparation of carboxylic acids……

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4. From Grignard

reagent

5. a) From acyl

halides

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Methods of preparation of carboxylic acids……

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b) From anhydrides

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Methods of preparation of carboxylic acids……

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6. From esters

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Physical properties of carboxylic acids

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Boiling point : Carboxylic acids > alcohols > aldehydes, ketones

Reason: This is due to more extensive intermolecular

hydrogen bonding between acid molecules.

The hydrogen bonds are not broken even in

the vapour phase. In fact, most of the

carboxylic acids are existing as dimer in the

vapour phase.

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Physical properties of carboxylic acids

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Solubility: Lower members are miscible in water due to

formation of hydrogen bonds with water

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ChProperties of carboxylic acids

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  1. Reactions involving cleavage of O-H bond

Acidity:Reactions with metals and alkalies

Effect of substituents on the acidity of

carboxylic acids

B) Reactions involving cleavage of C-OH bond

i) Formation of anhydride

ii) Esterification

iii) Reactions with PCl3 PCl5 and SOCl2

iv) Reaction with ammonia

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ChProperties of carboxylic acids

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C) Reactions involving –COOH group

i) Reduction

ii) Decarboxylation

  1. Substitution reactions in the Hydrocarbon part

i) Halogenation

ii) Ring substitution

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Chemical properties of carboxylic acids……….

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  1. Reactions involving cleavage of O-H bond

Acidity:Reactions with metals and alkalies

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Chemical properties of carboxylic acids……….

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  1. Reactions involving cleavage of O-H bond

Acidity:Reactions with metals and alkalies

Reason: Resonance stabilization of carboxylate anion

Carboxylic acids are more acidic than alcohols and phenols, why?

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Chemical properties of carboxylic acids……….

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  1. Reactions involving cleavage of O-H bond

Effect of substituents on the acidity of

carboxylic acids

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Chemical properties of carboxylic acids……….

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  1. Reactions involving cleavage of O-H bond

Effect of substituents on the acidity of carboxylic acids

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Chemical properties of carboxylic acids……….

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  1. Reactions involving cleavage of O-H bond

Effect of substituents on the acidity of carboxylic acids

Direct attachment of phenyl or vinyl group increases the acidity contrary to the decrease expected due to resonance effect

This is because of sp2

hybridized carbon

attached to carboxyl group.

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Chemical properties of carboxylic acids……….

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  1. Reactions involving cleavage of O-H bond

Effect of substituents on the acidity of carboxylic acids

EWG increases the

acidity of aromatic acids

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Chemical properties of carboxylic acids…….

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B) Reactions involving cleavage of C-OH bond

i) Formation of anhydride

ii) Esterification

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Chemical properties of carboxylic acids…….

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Mechanism of esterification

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Chemical properties of carboxylic acids…….

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B) Reactions involving cleavage of C-OH bond

iii) Reactions with PCl3 PCl5 and SOCl2

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Chemical properties of carboxylic acids…….

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B) Reactions involving cleavage of C-OH bond

iv) Reaction with ammonia

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Chemical properties of carboxylic acids…….

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B) Reactions involving cleavage of C-OH bond

iv) Reaction with ammonia

Synthesis of phthalimide

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Chemical properties of carboxylic acids…….

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C) Reactions involving –COOH group

i) Reduction

ii) Decarboxylation

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Chemical properties of carboxylic acids…….

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  1. Substitution reactions in the Hydrocarbon part

i) Halogenation: Hell –Volhard –Zelinsky reaction

ii) Ring substitution

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Uses of carboxylic acids

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1.Methanoic acid - rubber, textile,dyeing,leather and

electroplating industries

2. Ethanoic acid- solvent, food preservative

3. Benzoic acid- food preservative and perfume

4. Fatty acid- soaps and detergent

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Summary

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  • In this session we have studied
  • nomenclature,
  • preparation methods
  • important reactions of carboxylic acids
  • Also we have covered the important uses of carboxylic acids

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