Mechanism of selective oxidation of organic sulfides with oxo(salen)chromium(V) complexes

The selective oxidation of organic sulfides to sulfoxides by oxo(salen)chro mium(V) complexes in acetonitrile is overall second-order, first-order each in the oxidant and the substrate. The rate constant, k(2), values of sever al para-substituted phenyl methyl sulfides correlate linearly with Hammett sigma constants and the rho values are in the range of -1.3 to -2.7 with di fferent substituted oxo(salen)chromium(v) complexes. The reactivity of diff erent alkyl sulfides is in accordance with Taft's steric substituent consta nt, E-s. A mechanism involving direct oxygen atom transfer from the oxidant to the substrate rather than electron transfer is envisaged. Correlation a nalyses show the presence of an inverse relationship between reactivity and selectivity in the reaction of various sulfides with a given oxo(salen)chr omium(v) complex and vice versa. Mathematical treatment of the results show s that this redox system falls under strong reactivity-selectivity principl e (RSP).