New mechanism for the reaction of amines with zinc dithiocarbamates

This article reports a detailed reinvestigation of the reaction of bis(dial kyldithiocarbamato)zinc(II) (ZDAC) with amines. The reaction of primary ami nes with bis(dimethyldithiocarbamato)zinc(II) (ZDMC) results in the formati on of a 1,1,3-trisubstituted thiourea, a 1,3-disubstituted thiourea, dimeth ylammonium dimethyldithiocarbamate (DMADC), ZnS, and H2S. The ratio of form ation between the two thiourea products strongly depends on the reaction co nditions chosen. A new mechanism is proposed, which involves the formation of an amine-dithiocarbamic intermediate, from which the two most important products, a 1,1,3-trisubstituted and a 1,3-disubstituted thiourea, are form ed. Also, direct transformation of the 1,1,3-trisubstituted thiourea into t he 1,3-disubstituted thiourea via nucleophilic attack of the primary amine onto the thiocarboxy of the 1,1,3-trisubstituted thiourea was found to occu r, catalyzed by ZnCl2. The reaction of primary amines with ZDACs is catalyz ed by elemental sulfur, which has been attributed to sulfur insertion in th e zinc-ligand ring of the ZDAC, resulting in a higher reactivity of the ZDA C complex. Finally, when ZDACs are reacted with a secondary amine, no thiou rea products are formed and only a mixture of zinc dithiocarbamates is obta ined. (C) 2000 John Wiley & Sons, Inc.