Abstract:
Rates and products of the oxidation of diphenyl sulfide, phenyl
methyl sulfide, p-chlorophenyl methyl sulfide and diphenyl sulfoxide
have been determined. Oxidants included t-Bu02H alone, t-Bu02H plus
molybdenum or vanadium catalysts and the molybdenum peroxo complex
Mo0(02)2*HMPT. Reactions were chiefly carried out in ethanol at
temperatures ranging from 20° to 65°C.
Oxidation of diphenyl sulfide by t-Bu02H in absolute ethanol at
65°C followed second-order kinetics with k2 = 5.61 x 10 G M~1s"1, and
yielded only diphenyl sulfoxide. The Mo(C0)g-catalyzed reaction gave
both the sulfoxide and the sulfone with consecutive third-order kinetics.
Rate = k3[Mo][t-Bu02H][Ph2S] + k^[Mo][t-Bu02H][Ph2S0], where
log k3 = 12.62 - 18500/RT, and log k^ = 10.73 - 17400/RT.
In the absence of diphenyl sulfide, diphenyl sulfoxide did not
react with t-Bu02H plus molybdenum catalysts, but was oxidized by
t-Bu02H-V0(acac)2.
The uncatalyzed oxidation of phenyl methyl sulfide by t-Bu02H in
absolute ethanol at 65°C gave a second-order rate constant,
k = 3.48 x 10~"5 M^s""1. With added Mo(C0)g, the product was mainly
phenyl methyl sulfoxide; Rate = k3[Mo][t-Bu02H][PhSCH3] where
log k3 = 22.0 - 44500/RT. Both diphenyl sulfide and diphenyl sulfoxide react readily with the
molybdenum peroxy complex, Mo0(02)2'HMPT in absolute ethanol at 35°C,
yielding diphenyl sulfone.
The observed features are mainly in agreement with the literature
on metal ion-catalyzed oxidations of organic compounds by hydroperoxides.
These indicate the formation of an active catalyst and the complexation
of t-Bu02H with the catalyst. However, the relatively large difference
between the activation energies for diphenyl sulfide and phenyl methyl
sulfide, and the non-reactivity of diphenyl sulfoxide suggest the
involvement of sulfide in the production of an active species.
