OXIDATION OF ALKYL SULFIDES BY AQUEOUS PEROXYMONOSULFATE

The kinetics and mechanism of the oxidation of the alkyl sulfides dimethyl sulfide (DMS) and diethyl sulfide (DES) by peroxymonosulfate (HSO5-) in aqueous solution were studied as a function of pH, temperature, and ionic strength. The rate law was found to be -d[R2S]/dt = k1[R2S][HSO5-] + k2[R2S][SO5(2-)], where k1(DMS) = 0.13 +/- 0.09 M-1 s-1, k2(DMS) = 29.8 +/- 0.08 M-1 s-1, k1(DES) = 0.29 +/- 0.01 M-1 s-1, and k2(DES) = 11.1 +/- 1.0 M-1 s-1 (25-degrees-C; ionic strength, 0.2 M). The activation parameters for DMS and DES, respectively, are DELTA-H double-ended dagger k1 = 51.3 +/- 0.5 and 40.7 +/- 5.9 kJ mol-1, DELTA-S double-ended dagger k1 = -87.0 +/- 0.1 and -119 +/- 20 J K-1 mol-1, DELTA-H double-ended dagger k2 = 43.5 +/- 1.9 and 18.5 +/- 3.3 kJ mol-1, and DELTA-S double-ended dagger k2 = -70 +/- 7 and -164 +/- 18 J K-1 mol-1. Dimethyl sulfoxide, dimethyl sulfone, diethyl sulfoxide, and diethyl sulfone were identified as reaction products. A comparison of the relative rates of oxidation of DMS and DES by HSO5-, H2O2, and O3 shows that HSO5- may be a more important aqueous sink for the alkyl sulfides than H2O2. O3 is, however, likely to be the dominant aqueous oxidant under conditions that could be expected in remote marine clouds.