Acyl Chlorides & Esters (Edexcel International A Level Chemistry): Revision Note

Acyl Chlorides & Esters

Acyl groups Acyl groups can be built into many molecules using acyl chlorides or acid anhydrides (known as acylating agents) Acyl chlorides are derivatives of carboxylic acids by substitution of the -OH group by a chlorine atom Acyl chlorides are named by identifying the parent hydrocarbon chain and adding the suffix -oyl chloride They can also be named by removing the -oic acid from the carboxylic acid and adding -oyl chloride

• Acid anhydrides are also derivatives of carboxylic acids formed by substitution of the -OH group by an alkanoate

  • Acid anhydrides are named by identifying the parent hydrocarbon chain and adding the suffix -oic anhydride

  • They can also be named by removing the -oic acid from the carboxylic acid and adding -oic anyhydride

Ethanoic acid derivatives

• Acyl chlorides are reactive organic compounds that undergo many reactions such as nucleophilic addition-elimination reactions

• In nucleophilic addition-elimination reactions, the nucleophilic addition of a small molecule across the C=O bond takes place followed by elimination of a small molecule

• Examples of these nucleophilic addition-elimination reactions include:

  • Hydrolysis

  • Reaction with alcohols to form esters

  • Reaction with ammonia and primary amines to form amides

Hydrolysis

• The hydrolysis of acyl chlorides results in the formation of a carboxylic acid and HCl molecule

• This is a nucleophilic addition-elimination reaction

  • A water molecule adds across the C=O bond

  • A hydrochloric acid (HCl) molecule is eliminated

• An example is the hydrolysis of propanoyl chloride to form propanoic acid and HCl

Acyl chlorides are hydrolysed to carboxylic acids

Formation of esters

• Acyl chlorides can react with alcohols to form esters

• The esterification of acyl chlorides is also a nucleophilic addition-elimination reaction

  • The alcohol adds across the C=O bond

  • A HCl molecule is eliminated

Acyl chlorides undergo esterification with alcohols to form esters

Formation of amides

• Acyl chlorides can form amides with primary amines and concentrated ammonia

• The nitrogen atom in ammonia and primary amine has a lone pair of electrons which can be used to attack the carbonyl carbon atom in the acyl chlorides

• The product is an amide (when reacted with ammonia) or N-substituted amide (when reacted with primary amines)

• This is also an example of a nucleophilic addition-elimination reaction as

  • The amine or ammonia molecule adds across the C=O bond

  • A HCl molecule is eliminated

Acyl chlorides undergo reactions with ammonia and primary amines to form amides