Acyl chlorides are named by removing the -oic acid suffix from the parent carboxylic acid and replacing it with the suffix -oyl chloride.

For example, the acyl chloride of ethanoic acid is ethanoyl chloride.

A carboxylic acid derivative is a compound that can be hydrolysed to form the parent carboxylic acid.

Examples of carboxylic acid derivatives include esters, acyl chlorides, acid anhydrides, and amides.

Acyl chlorides are also called acid chlorides.

This mechanism is addition-elimination.

Acyl chlorides react with alcohols to form esters and hydrogen chloride as a by-product.

For example, the reaction between ethanoyl chloride and ethanol produces ethyl ethanoate and HCl:

CH₃COCl + C₂H₅OH ➔ CH₃COOC₂H₅ + HCl

Acyl chlorides react with phenols to form phenyl esters and hydrogen chloride as a by-product.

For example, the reaction between ethanoyl chloride and phenol produces phenyl ethanoate and HCl:

CH₃COCl + C₆H₅OH ➔ CH₃COOC₆H₅ + HCl

Acyl chlorides undergo hydrolysis with water to form carboxylic acids. This is a vigorous reaction that produces steamy hydrogen chloride fumes.

For example, the reaction between ethanoyl chloride and water produces ethanoic acid and HCl:

CH₃COCl + H₂O ➔ CH₃COOH + HCl

Acyl chlorides react with ammonia to form primary amides and ammonium chloride as a by-product.

For example, the reaction between ethanoyl chloride and ammonia produces ethanamide and NH₄Cl:

CH₃COCl + 2NH₃ ➔ CH₃CONH₂ + NH₄Cl.

Acyl chlorides react with primary amines to form secondary amides and an ammonium salt as a by-product.

For example, the reaction between ethanoyl chloride and methylamine produces N-methylethanamide and CH₃NH₃Cl:

CH₃COCl + 2CH₃NH₂ ➔ CH₃CONHCH₃ + CH₃NH₃Cl.

Acyl chlorides are made directly from the reaction of their parent carboxylic acid with either:

1. Thionyl chloride (SOCl₂).
2. Phosphorus(V) chloride (PCl₅).
3. Phosphorus(III) chloride (PCl₃) and heat.

For example, the equation for the preparation of ethanoyl chloride from ethanoic acid using SOCl₂ is:

CH₃COOH + SOCl₂ ➔ CH₃COCl + SO₂ + HCl

The ease of hydrolysis increases in the order: aryl chlorides < alkyl chlorides < acyl chlorides.

Acyl chlorides hydrolyse most readily because the carbon bonded to the chlorine is strongly electron deficient, being attached to two electronegative atoms (i.e. oxygen and chlorine). This makes it readily attacked by a nucleophile like water.

Alkyl chlorides require strong alkaline conditions to hydrolyse, as the carbon bonded to chlorine is less electron deficient.

Aryl chlorides don't undergo hydrolysis because the carbon-chlorine bond has some double bond character due to the overlap of a lone pair of electrons on the chlorine atom with benzene's delocalised ring of π-electrons. This makes the C-Cl bond very strong and resistant to cleavage.