It is “2-imino-4-thiazolidinones” and not thiohydantoins as the reaction product of 1,3-disubstituted thioureas and chloroacetylchloride

The products obtained by the reaction of 1,3-disubstituted thioureas with chloroacetylchloride are actually 2-imino-4-thiazolidinone derivatives and not thiohydantoins as previously reported (M. Kidwai, R. Venkataraman and B. Dave, Green. Chem., 2001, 3, 278). A highly efficient method for the preparation of 2-imino-4-thiazolidinones has been achieved from both symmetrical and unsymmetrical thioureas in the absence of base. The reaction gives a regioselective product for unsymmetrical thiourea which is dependent on the pKa's of the amines. For unsymmetrical thiourea, regioselective 2-imino-4-thiazolidinone formation takes place with the amine attached to the thiourea having lower pKa as part of the imino component and the amine having higher pKa contributes to the other heterocyclic nitrogen.