ELECTROCHEMICAL STUDIES OF SOME DITHIADIAZOLYLIUM CATIONS - EVIDENCE FOR THE DITHIADIAZOLIDE ANION, [PHCNSSN]-

A series of para-substituted aryldithiadiazolylium salts [p-XC6H4CNSSN][Y] (X = H, Me, CF3, MeO, MeS, NO2, F, Cl, Br, CN or CNSSN+; Y = Cl or AsF6) and [p-XC6H4CNSNS][AsF6] (X = H, Me, CF3, MeO, MeS, NO2, F, Cl, Br or CNSNS+) has been prepared. An electrochemical study of both 1,2,3,5- and 1,3,2,4-dithiadiazolylium derivatives, as the hexafluoroarsenate(V) salts, showed reversible redox behaviour, forming the corresponding dithiadiazolyl radicals. The half-wave reduction potentials, E1/2(red), for the two isomeric dithiadiazolylium cations showed linear free-energy relationships between E1/2(red) and the Hammett value, sigma(p), for the substituent group X; the sigma(p) values for CNSSN+ and CNSNS+ rings have been calculated at +0.537 +/- 0.005 and +0.57 +/- 0.02 respectively. A second reduction process was also observed for both 1,2,3,5- and 1,3,2,4-dithiadiazolylium cations, indicative of the formation of the dithiadiazolide anion, [p-XC6H4CNSSN)-; a preparative-scale reduction of (PhCNSSN)2 using sodium amalgam and 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) provided a yellow air-sensitive solid, [Na(18-crown-6)][PhCNSSN].