Acylation is the addition of an acyl group, RCO, to a molecule. Acyl chlorides and acid anhydrides acylate four types of nucleophile. Using ethanoyl chloride:Water gives a carboxylic acid:
CH3COCl + H2O → CH3COOH + HCl
Alcohols give an ester:
CH3COCl + CH3CH2OH → CH3COOCH2CH3 + HCl
Ammonia gives a primary amide. The HCl formed reacts with a second ammonia molecule, so two moles are needed:
CH3COCl + 2NH3 → CH3CONH2 + NH4Cl
Primary amines give an N-substituted amide, and the second amine molecule forms a salt:
CH3COCl + 2CH3NH2 → CH3CONHCH3 + CH3NH3+Cl−
The products are ethanoic acid, ethyl ethanoate, ethanamide and N-methylethanamide. The prefix N- shows that the methyl group is on the nitrogen.With an acid anhydride the organic products are the same, but the by-product is a carboxylic acid, e.g. (CH3CO)2O + CH3CH2OH → CH3COOCH2CH3 + CH3COOH.Worked example: predict the product of propanoyl chloride and ethylamine. The acyl group CH3CH2CO joins the nitrogen, which keeps one H and its ethyl group: CH3CH2CONHCH2CH3, N-ethylpropanamide. Making esters this way is faster than esterification and is not reversible.
Alcohols give an ester:
Ammonia gives a primary amide. The HCl formed reacts with a second ammonia molecule, so two moles are needed:
Primary amines give an N-substituted amide, and the second amine molecule forms a salt:
The products are ethanoic acid, ethyl ethanoate, ethanamide and N-methylethanamide. The prefix N- shows that the methyl group is on the nitrogen.With an acid anhydride the organic products are the same, but the by-product is a carboxylic acid, e.g. (CH3CO)2O + CH3CH2OH → CH3COOCH2CH3 + CH3COOH.Worked example: predict the product of propanoyl chloride and ethylamine. The acyl group CH3CH2CO joins the nitrogen, which keeps one H and its ethyl group: CH3CH2CONHCH2CH3, N-ethylpropanamide. Making esters this way is faster than esterification and is not reversible.