6.1.3 Carboxylic Acids and Esters

Functional group of a carboxylic acid

-COOH (C=O and C-OH)

Naming carboxylic acids

-oic acid

Solubility of carboxylic acids in water

Yes. Acid group can form hydrogen bonds with water molecules.

Intermolecular forces in carboxylic acids

Hydrogen bonds in solid state - very strong.

Esters formation

Formed from carboxylic acids and alcohols.

General formula of esters

RCOOR' (C=O, C-O-C)

Reaction of ethanoic acid with propan-1-ol

CH3COOH + CH3CH2CH2OH → CH3COOCH2CH2CH3 + H2O

Naming esters

Start with the alcohol group that has replaced the hydrogen, then acid part e.g. propyl (from alcohol) ethanoate (from carboxylic acid).

Characteristic physical properties of esters

Volatile, pleasant fruity smells e.g. apple, pear drops.

Uses of esters

Flavourings, perfumes (both for longer chains), solvents (short chains), plasticisers.

Distinguishing carboxylic acids from other -OH containing compounds

Add NaHCO3, acids will produce sodium salt, water and carbon dioxide.

Reaction of ethanoic acid with NaOH

CH3COOH + NaOH → H2O + CH3COO-Na+

Reaction of ethanoic acid with Na2CO3

2CH3COOH + Na2CO3 → 2CH3COO-Na+ + H2O + CO2

Reaction of ethanoic acid with calcium oxide

2CH3COOH + CaO → (CH3COO)2Ca + H2O

Catalyst for the formation of esters

Concentrated strong acid e.g. H2SO4.

Catalyst for the hydrolysis of esters

Dilute strong acid e.g. H2SO4.

Alternative method of hydrolysis

Base hydrolysis.

Advantages of base hydrolysis

Reaction goes to completion due to neutralisation by base - more product in the mixture than acid catalysed hydrolysis.

Neutralisation

Reaction goes to completion due to neutralisation by base - more product in the mixture than acid.

Carboxylic acid derivatives

Molecules that have the acyl group as part of their structure, formed from carboxylic acids.

Acyl chlorides

RCOCl

Acid anhydrides

RCOOCR / (RCO)2O

Formation of acyl chloride

React a carboxylic acid with SOCl2.

Products of acylation with ammonia

An amide.

Reaction of ethanoyl chloride and ammonia

CH3COCl + 2NH3 → CH3CONH2 + NH4Cl.

Products of acylation with primary amine

N-substituted amide.

Reaction of ethanoyl chloride and methylamine

CH3COCl + CH3NH2 → CH3CONHCH3 + CH3NH3Cl.

Products of acylation with alcohol

An ester.

Reaction of ethanoyl chloride and ethanol

CH3COCl + CH3CH2OH → CH3COOCH2CH3 + HCl.

Products of acylation with water

Carboxylic acid (hydrolysis produces an ester linkage).

Name of reaction with water as nucleophile

Hydrolysis.

Reaction of ethanoyl chloride and water

CH3COCl + H2O → CH3COOH + HCl.