Kinetics and mechanism of (salen)Mn^III‐catalysed oxidation of organic sulfides with sodium hypochlorite

Abstract

The oxidation of organic sulfides with several substituted oxo(salen)manganese(V) complexes was investigated in 90% acetonitrile–10% water and the reaction is second‐order overall, first‐order each in sulfide and complex. Electron‐releasing substituents in sulfides and electron‐withdrawing substituents in oxo(salen)manganese(V) complexes accelerate the rate of oxidation. The second‐order rate constants for the oxidation of p‐substituted phenyl methyl sulfides follow a linear Hammett relationship with ρ = −1.85. However, correlation between log k2 and 2σ is excellent with ρ = 0.48 for the oxidation of thioanisole by substituted oxomanganese(V) complexes. The rate of oxidation of alkyl phenyl sulfides and dialkyl sulfides with oxo complexes was also examined and the reactions show a moderate steric effect. Substituent, acid and solvent effect studies reveal the operation of an SN2 mechanism. Copyright © 2003 John Wiley & Sons, Ltd.

Mechanism of oxidation of aryl methyl sulfoxides with sodium hypochlorite catalyzed by (salen)MnIII complexes

“…This demonstrates [29,30] that PyO is not binding with oxo(salen)manganese(V) complex and has no catalytic effect during the oxidation process. Similar results have been obtained in the epoxidation of olefins [18] and oxidation of aryl methyl sulfides [7,15] by oxo(salen)manganese(V) complexes. Kinetic studies at different concentrations of trichloroacetic acid and solvent compositions have been carried out and the rate data are collected in Table 2.…”

“…2, r = 0.999, s = 0.012). It is interesting to compare the present results with those observed for the oxidation of organic sulfides (Table 4) [15,16]. The electronic effect is more pronounced with sulfoxide oxidation and the ρ-value is uniformly higher with sulfoxides.…”

“…The effect of substituents at the 7,7 -positions of salen ligand of oxo(salen)manganese(V) complexes on the reaction rate was studied using 2a, 2e and 2f for the oxidation of phenyl methyl sulfoxide. The rate data in Table 1 show that the presence of methyl or phenyl group at the 7,7 -positions slightly reduces the rate, as in the case of sulfide oxidation [15].…”

“…When a clear brown solution of (salen)Mn III is treated with equimolar quantities of sodium hypochlorite, it immediately turns dark brown, indicating the formation of oxomanganese(V) species [15] (λ max ∼ 530 nm). The dark brown solution, on standing, faded to the original light brown within 2-3 h. When the same experiment was carried out in the presence of methyl phenyl sulfoxide (MPSO), the dark brown colour is discharged to original light brown within 40-50 min and methyl phenyl sulfone was isolated in 74% yield (Eq.…”

“…As the isolation of pure oxo(salen)manganese(V) complexes is difficult [7][8][9][10]15,18], they were generated in situ for the studies reported here.…”