Topic 25 of 34
An acyl chloride reacts readily with water, alcohols, phenols and amines
Its polar carbonyl and leaving chloride make it more reactive than an alkyl or aryl chloride.
A-Level 9476 (2026-2027)
An acyl chloride reacts readily with water, alcohols, phenols and amines
Its polar carbonyl and leaving chloride make it more reactive than an alkyl or aryl chloride.
| Reagent | Organic product | Representative equation |
|---|---|---|
| Water | Carboxylic acid; rapid hydrolysis under ordinary conditions. | CH3COCl + H2O → CH3COOH + HCl. |
| Alcohol | Ester. | CH3COCl + C2H5OH → CH3COOC2H5 + HCl. |
| Phenol or phenoxide | Phenyl ester; base can increase nucleophilicity and remove acid. | C6H5COCl + C6H5OH → C6H5COOC6H5 + HCl. |
| Primary amine | N-substituted amide; excess amine or another base removes HCl. | R'COCl + 2RNH2 → R'CONHR + RNH3+Cl-. |
Phenyl benzoate is C6H5COOC6H5, formed from benzoyl chloride and phenol/phenoxide. The phenyl group after the ester oxygen comes from phenol; the benzoyl portion comes from the acid chloride. Phenol does not esterify readily by the ordinary carboxylic-acid/alcohol method, so the acyl-chloride route is a useful distinction.
In an acyl chloride, nucleophilic attack occurs at the strongly δ+ carbonyl carbon; addition can be followed by loss of chloride. Hydrolysis is consequently much easier than in an alkyl chloride, which requires substitution at a saturated carbon and usually heating with an aqueous nucleophile. An aryl chloride such as chlorobenzene is still more resistant under those ordinary conditions because delocalisation strengthens C-Cl and the ring hinders the usual substitution pathways.
Worked example
Distinguish three chlorides by water and hydrolysis
Compare ethanoyl chloride, chloroethane and chlorobenzene with water under ordinary conditions, then with heated aqueous NaOH.
- Ethanoyl chloride hydrolyses readily with water, releasing HCl and forming ethanoic acid.
- Chloroethane does not show the same immediate vigorous hydrolysis but reacts on heating with aqueous hydroxide to give ethanol and chloride.
- Chlorobenzene resists the ordinary heated aqueous-hydroxide substitution conditions used for halogenoalkanes.
Ease of hydrolysis: acyl chloride > comparable alkyl chloride > aryl chloride under the stated conditions. This comparison concerns the bonding environment, not simply the presence of chlorine.