Anhydrocarboxylate and anhydrosulphite derivatives of α-thiocarboxylic acids: Synthesis, purification and characterisation

The syntheses of anhydrosulphite and anhydrocarboxylate derivatives of α-thioglycollic and α-thiolactic acids by reaction of thionyl chloride and phosgene with both the parent acids and their copper salts have been examined. The preferred method, involving direct reaction with the acid, produced reasonable (30–65% depending on acid structure) yields of the required compounds. Successful synthesis of the anhydrocarboxylate of α-thioisobutyric acid involved the simultaneous addition of phosgene and pyridine to the acid solution in order to promote formation and cyclisation of the intermediate. Characterisation of the purified products was carried out by infrared and mass spectrometry together with gas evolution techniques.