Alcohols & Acyl Chlorides (Cambridge (CIE) A Level Chemistry): Revision Note

Reaction of Alcohols With Acyl Chlorides

• Acyl chlorides are reactive organic compounds with a -COCl functional group

• The carbonyl carbon is electron-deficient and has a partial positive charge

• It is therefore susceptible to nucleophilic attack

• The carbon-chlorine bond breaks and white fumes of hydrogen chloride, HCl, are formed

Reaction with alcohols and phenols

• Acyl chlorides react with alcohols and phenols to form esters via an addition–elimination mechanism

• The -OH group acts as a nucleophile and attacks the carbonyl carbon to substitute the chlorine atom

• Forming esters from acyl chlorides rather than carboxylic acids is more effective because:

  • Acyl chlorides are more reactive (so they produce the ester faster)

  • Acyl chloride reactions go to completion (so more of the ester is produced)

Reaction with alcohols

• The reaction of acyl chlorides with alcohols is vigorous and white fumes of HCl gas are formed

Esterification of an aliphatic alcohol using an acyl chloride

Acyl chlorides react vigorously with alcohols to form esters

Reaction with phenols

• Acyl chlorides react with phenols at room temperature, more slowly than with alcohols

• Adding a base such as NaOH forms the more nucleophilic phenoxide ion and speeds the reaction up

  • The base is needed to deprotonate the phenol and form a phenoxide ion

  • The phenoxide ion is a better nucleophile than the original phenol molecule and will be able to attack the carbonyl carbon

Esterification of phenol using an acyl chloride

• The overall equation is:

ethanoyl chloride + phenol + sodium hydroxide → phenyl ethanoate + sodium chloride + water

CH₃COCl + C₆H₅OH + NaOH → CH₃COOC₆H₅ + NaCl + H₂O

• A base is needed to form a phenoxide ion which is a better nucleophile than phenol

• This means that nucleophilic attack on the carbonyl carbon can more readily occur