Kinetics and mechanism of (salen)Mn^III–catalysed hydrogen peroxide oxidation of alkyl aryl sulphides

Abstract

The kinetics of (salen)MnIII complexes catalysed oxidation of aryl methyl and alkyl phenyl sulphides with hydrogen peroxide have been investigated at 25°C in 80% acetonitrile – 20% water spectrophotometrically. The reaction follows first‐order kinetics in (salen)MnIII complex and zero‐order kinetics in hydrogen peroxide. The order of the reaction with respect to sulphide is fractional and saturation in reaction rate occurs at higher sulphide concentrations. The pseudo first‐order rate constants have been analysed as per Michaelis–Menten kinetics to obtain the values of k2, the oxidant‐substrate complex decomposition rate constant, and K, the oxidant‐substrate complex formation constant. The effects of nitrogenous bases, free radical inhibitor and changes in solvent composition have also been studied. A suitable mechanism, supported by electronic‐oxidant and electronic‐substrate effect studies, involving a manganese(III)‐hydroperoxide complex as reactive species has been proposed. Copyright © 2007 John Wiley & Sons, Ltd.

Kinetic study of the manganese‐based catalytic hydrogen peroxide oxidation of a persistent azo‐dye

“…24 However, simpler pseudo-first-order kinetics has been used successfully in the literature to account for the observed experimental rates. 21,22 The use of catalysts developed for the detergent industry 23,25 combined with hydrogen peroxide to remove dyes from wastewater is useful and worth studying. The present investigation has been undertaken with this in mind and also because of the environmental impact of azo-dyes.…”

“…20 These manganese based catalysts have high selectivity and activity towards organic compounds that can be easily transformed to, for example, epoxides, ketones and alcohols. Other relevant catalysts include those using manganese complexes of N,N -ethylenebis(salicylideneaminato) for the removal of sulphides 21 and dyes. 22 Manganese complexes containing tripodal ligands based on tris(2-aminoethyl)amine have also been used in oxidation with hydrogen peroxide as applied to cleaning and disinfection processes.…”

Chemoselective Sulfide and Sulfoxide Oxidations by CpMo(CO)3Cl/HOOR: a DFT Mechanistic Study

“…In these studies, sulfide oxidation is considered to obey the concerted Sharpless mechanism, consisting of an external nucleophilic attack of the sulfur atom (from the outer coordination sphere) onto an electrophilically activated peroxygen, followed by heterolytic cleavage of the O−O bond to form sulfoxide. Owing to the nucleophilic character of the attack, the reactivity increases with the electron richness of the sulfides. , Some rare examples of inner-sphere (intramolecular) mechanisms of sulfide oxidation have also been reported: e.g., in Ti and Mn systems. The proposed mechanism involves the coordination of the sulfide to the metal center, followed by the nucleophilic attack of the coordinated sulfide onto the coordinated peroxide.…”

Selective H2O2 oxidation of organic sulfides to sulfoxides catalyzed by cobalt(III)–salen ion

“…The reaction constant, ρ, value lies between -0.8 to -1.0 for Co(III)-salen catalyzed oxidation. The reported ρ value is -0.85 for the kinetics of Mn(III)-salen complexes catalyzed oxidation of aryl methyl sulfides with hydrogen peroxide [52]. The ρ values obtained for the Cr(III)-salen catalyzed oxidation of sulfides ranges between -1.5 to -1.8 [2g,2i,53].…”