• Acyl chlorides undergo?addition-elimination?reactions such as?hydrolysis, esterification?reactions to form esters, and?condensation?reactions to form?amides
• The general mechanism of these 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
  • The lone pair on the oxygen atoms carry out an?initial attack?on the carbonyl carbon
  • 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 or phenols act as a?nucleophile
  • The lone pair on the oxygen atoms carry out an?initial?attack on the carbonyl carbon
  • This is again followed by the elimination of an HCl molecule
• With phenols, the reaction requires?heat?to proceed and needs to be carried out in the presence of a?base
• The base?deprotonates?the phenol to form a?phenoxide?ion which is a?better nucleophile?than the phenol molecule
  • The?phenoxide ion?carries out an?initial attack?on the carbonyl carbon
  • A small molecule of NaCl is eliminated

Reaction mechanism of the esterification of acyl chlorides with alcohols

Reaction mechanism of the esterification of acyl chlorides with phenols

Formation of amides: reaction mechanism

• The nitrogen atom in?ammonia?and?primary/secondary amines?act as a?nucleophile
  • The lone pair on the nitrogen atoms carry out an?initial?attack on the carbonyl carbon
  • This is followed by the elimination of an HCl molecule
• Both reactions of acyl chlorides with ammonia and amines are?vigorous?however there are also differences
  • With?ammonia?- The product is a?non-substituted amide?and?white fumes?of HCl are formed
  • With?amines -?The product is a?substituted amide?and the HCl formed reacts with the?unreacted amine?to form a?white organic ammonium salt

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

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