Condensation polymerization of N‐dithiocarbonyl alkoxyearbonyl amino acids. Part V. Studies on reaction mechanism

N‐Dithiocarbonyl ethoxycarbonyl amino acids (DTE‐amino acids) (I) are easily converted to high molecular polypeptides by heating in dioxane. To elucidate the reaction mechanism, the formation of by‐products or intermediates in the polymerization of DTE‐glycine and ‐alanine were studied. Thiazolid‐2.5‐dione (IV) and 2‐thio‐oxazolid‐ 5 ‐one (III) were isolated as by‐products. (III) is unstable and changes to polypeptide and (IV). The IR‐absorption of a isothiocyanate group is observed keeping (I) and (III) in KBr disks at room temperature and in the initial stage of the polymerization of (I). These results suggest the following predominant mechanism for the formation of poly‐peptides proceeding via the isothiocyanate carboxylic acid (II): magnified image