90 Reactions
90.1 Acid Chloride Formation
Carboxylic acids are converted to acid chlorides by a range of reagents: SOCl 2 , PCl 5 or
PCl 3 are the usual reagents. Other products are HCl & SO 2 , HCl & POCl 3 and H 3 PO 3
respectively. The conditions must be dry, as water will hydrolyse the acid chloride in a
vigorous reaction. Hydrolysis forms the original carboxylic acid.
CH 3 COOH + SOCl 2 →CH 3 COCl + HCl + SO 2
C 6 H 5 COOH + PCl 5 →C 6 H 5 COCl + HCl + POCl 3
3 CH 3 CH 2 COOH + PCl 3 →3 CH 3 CH 2 COCl + H 3 PO 3
90.2 Esterification
Alcohols will react with acid chlorides or carboxylic acids to form esters. This reaction is
catalyzed by acidic or basic conditions. See alcohol notes.
C 6 H 5 COCl + CH 3 CH 2 OH→C 6 H 5 COOCH 2 CH 3 + HCl
With carboxylic acids, the condensation reaction is an unfavourable equilibrium, promoted
by using non-aqueous solvent (if any) and a dehydrating agent such as sulfuric acid (non-
nucleophilic), catalyzing the reaction).
CH 3 COOH + CH 3 CH 2 CH 2 OH = CH 3 COOCH 2 CH 2 CH 3 + H 2 O
Figure 184 Ethanoic Acid reacts with Propanol to form Propyl Ethanoate
Reversing the reaction is simply a matter of refluxing the ester with plenty of aqueous acid.
This hydrolysis produces the carboxylic acid and the alcohol.
C 6 H 5 COOCH 3 + H2O→C 6 H 5 COOH + CH 3 OH