THE DIMETHYLHYDROXYSULFURANYL RADICAL

By use of pulse radiolysis the one-electron reduction potentials, E(0) (DMS(.+)/DMS) and E(0)((DMS)(2)(.+)/2DMS) (dimethyl sulfide, DMS) were determined to be 1.66 +/- 0.03 and 1.40 +/- 0.02 V vs NHE, respective ly. DMS(.+) was found to be in equilibrium with DMSOH(.) with a pK(a) = 10.2. The conditional equilibrium constant for the reaction DMSOH(.) + DMS reversible arrow (DMS)2(.+) + OH- was found strongly dependent on both ionic strength and DMS concentration. In the thermodynamic lim it this equilibrium constant is approximate to 1.3. The dimerization r eaction DMS(.+) + DMS reversible arrow (DMS)2(.+) was shown to have it s equilibrium constant between 10(4) and 5 x 10(4) M(-1). DMSOH(.) rea cts with O-2 with a rate constant of 2 x 10(8) M(-1) s(-1), independen t of pH (11-14). From this and other observations, we estimate the pK( a) for deprotonation of DMSOH(.) to exceed 17. From spectral and kinet ic data, the maximum lifetime of the radical (DMS)(2)OH. was predicted to be 10 ns. The stability of DMS-X(.) (X = OH, I, Br, Cl) in aqueous solution was shown to correlate with the one-electron reduction poten tial of X(.). Comparison of gaseous and aqueous behavior of DMS-OH. re veals that aqueous solvation strongly stabilizes the S-O bond against dissociation into DMS and OH.. The Gibbs free energy of solvation of D MSOH(.) was calculated to be -12 +/- 3 kcal/mol, an unusually large va lue for a neutral species.