Ethanoic acid derivatives

Answer:

• 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?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

• Acyl chlorides undergo?nucleophilic?addition-elimination?reactions such as?hydrolysis, esterification?reactions to form esters, and?condensation?reactions to form?amides
• The general mechanism of these nucleophilic addition-elimination reactions involve two steps:
  • Step 1 -?Addition of a?nucleophile?across the C=O bond
  • Step 2 -?Elimination of a?small molecule?such as HCl?or H2O

   

Mechanism of hydrolysis of acyl chlorides

• In the?hydrolysis?of acyl chlorides, the water molecule acts as a?nucleophile
  • Step 1 - Nucleophilic addition;?the lone pair on the oxygen atoms carry out an?initial attack?on the carbonyl carbon
  • Step 2 - Elimination;?this is followed by the elimination of a hydrochloric acid (HCl) molecule

   

Reaction mechanism of the hydrolysis of acyl chlorides

Formation of esters: reaction mechanism

• In the?esterification?reaction of acyl chlorides, the alcohols act as a?nucleophile
  • Step 1 - Nucleophilic addition;?the lone pair on the oxygen atoms carry out an?initial?attack on the carbonyl carbon
  • Step 2 - Elimination;?this is again followed by the elimination of an HCl?molecule

   

Reaction mechanism of the esterification of acyl chlorides with alcohols

Formation of amides: reaction mechanism

• The nitrogen atom in?ammonia?and?primary amines?act as a?nucleophile
  • Step 1 - Nucleophilic addition;?the lone pair on the nitrogen atoms carry out an?initial?attack on the carbonyl carbon
  • Step 2 - Elimination;?this is followed by the elimination of an HCl?molecule
  • Step 3 - Acid-Base reaction;?the HCl?formed would immediately react with excess ammonia to give ammonium chloride in an acid-base reaction

   

Reaction mechanism of the formation of amides from acyl chlorides with ammonia

Reaction mechanism of the formation of amides from acyl chlorides with primary amines