Studies on some 1,2,4-dithiazolium salts

Abstract

3-Alkylthio-l,2,4-dithiazolium salts are most conveniently made by alkylation of the Corresponding 1,2,4-dithiazole-3-thiones by dimethyl sulfate. These salts readily undergo nucleophilic attack by amines in position 3, with loss of a methylthio group. Hydrogen peroxide oxidation, or chlorination, of the thiones gives the corresponding dithiazole-)-ones.Canadian Journal of Chemistry, 48,2142Chemistry, 48, (1970 T o provide suitable examples of the 1,2,4-dithiazolium cation (1) for study, we have investigated some of their preparations and reactions. One suitable approach t o this system appeared to be from the readily accessible (1, 2) 3H-1,2,4-dithiazole-3-thiones (2), since it was expected that they might react similarly t o the 3H-1,2-dithiole-3-thiones, which can be converted by several methods (3-9, into examples of the 1,2-dithiolium cation.The first reaction studied was the alkylation of the thiones (2), to provide a convenient syntliesis of the 3-alkylthio-l,2,4-dithiazolium cations (3a-i). The preparation of one of these (3a) using methyl iodide as the alkylating agent has been reported (1). Also, use of triethyloxonium fluoroborate (6) provides examples of the 3-ethylthio cation (36). However, the first of these methods is unsatisfactory in that the 3-methylthio-1,2,4-dithiazolium iodide (3a) is insufficiently soluble t o provide a convenient study of its properties. The latter method is also inconvenient in that it requires prior synthesis of triethyloxonium fluoroborate.A much more convenient method utilized dimethyl sulfate at 80". The thiones, 2a-g, were readily alkylated and treatment of the reaction solutions with perchloric acid afforded the 3-methylthio salts, 3c-i, as their perchlorates in good yields. These were stable, bright colored, and readily soluble in acetic acid or nitromethane, permitting study of their properties. The reactions of these salts with ainines are similar to the reaction of various 1,Zdithiolium salts with amines (7-9). 3H-1,2,4-Dithiazole-3-tliiones (2) are reported to undergo nucleophilic attack by primary amines (1) at position 5 of the ring, with the eventual formation of thioamides. However, nucleophilic attack on the 3-alkylthio salts 3 by primary amines occurs at position 3, with subsequent elimination of methanethiol. The 3-arylimino products 4 appear t o be rather reactive, and in two cases, the imines 4a, b, formed by reaction of aniline with the salts 312, d respectively, could not be isolated, although a preparation of the imine 4a has been reported recently (10) by another method. Instead, in these experiments, further addition products 5 with the amine were isolated. Only in the reaction of the salt (3d) with p-toluidine was the imine 4c isolated.further additions probably occurred at position 5 rather than at position 3 to give the compounds 5a, b or tautomers rather than the isomeric compounds 6 since nucleophilic attack of ainine to the isoelectronic dithiazolethiones 2 takes place at position 5. This structure is also indicated by nuclear magnetic reso...