Reactions of single-electron oxidation and reduction of sulfides of the azulene series

Single-electron oxidation in acetonitrile and reduction in DMF of sulfides of 3-RS-1,4-dimethyl-7-ethylazulenes (R = Me, Et, Ph, p-MeC6H4, p-MeOC6H4, N-1-phenyltetrazolyl) leads to stable radical cations and radical anions, r espectively. The found reduction potentials of sulfides of the azulene seri es are close to those of natural and synthetic bioantioxidants. In the radi cal cations the unpaired electron is essentially delocalized over the cyclo pentadienyl fragment of the molecule, and the sulfide group in large measur e defines the distribution of spin density. In the radical anion spin densi ty is delocalized in the tropylium cycle, and the influence of the sulfide group is insignificant. Electrochemical oxidation of unsubstituted 1,4-dime thyl-7-ethylazulene results in the formation of a dimeric radical cation.