Studies of the reactions of the anhydrosulphites of α-hydroxy-carboxylic acids. Part III. Purification and polymerisation of glycollic acid anhydrosulphite

Abstract

The synthesis of glycollic acid anhydrosulphite from cupric glycollate has been examined and chloroacetyl chloride shown to be the main impurity. A reliable method of purification, by use of silver oxide, has been devised. The ring-opening reactions of the anhydrosulphite with amines and alcohols have been examined and found to resemble the corresponding reactions of lactic acid anhydrosulphite. Polymerisation of the anhydrosulphite proceeds by two competing processes; one involves thermal decomposition to the α-lactone which then takes part in a chain-propagation process, whereas the other proceeds by direct attack of the hydroxyl-terminated chain on the anhydrosulphite ring. The latter process is analogous to the ring-opening reaction with alcohols. Supporting kinetic results are presented and compared with those for anhydrosulphites previously studied.