Kinetics and mechanism of oxidation of aryl methyl sulfoxides with (salen)MnIII/H2O2 catalytic system

✍ Scribed by Arunachalam Chellamani; Paramasivan Sengu; Naina Mohamed Ismail Alhaji

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 413 KB
• Volume: 317
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/j.molcata.2009.11.002

✦ Synopsis

The kinetics of (salen)Mn III complexes-catalysed oxidation of aryl methyl sulfoxides with hydrogen peroxide in 80% acetonitrile-20% water solvent mixture at 25 • C has been followed spectrophotometrically. The reaction is first-order in (salen)Mn III , zero-order in hydrogen peroxide and fractional-order in sulfoxide. Also, it has been found that nitrogenous bases affect the oxidation, while free-radical inhibitor does not. However, an increase in the water content of the solvent mixture causes an increase in the rate of reaction. Stoichiometry between H 2 O 2 and sulfoxide has been found to be 1:1 and the product analysis confirms the formation of sulfone and the regeneration of (salen)Mn III complex. These observations have been well analyzed in favor of a Michaelis-Menten type mechanism, involving a manganese(III)-hydroperoxide complex as the reactive species. Using the derived rate law, the oxidant-substrate complex formation constant, K and the oxidant-substrate complex decomposition rate constant, k 2 have been evaluated. The proposed mechanism has been well supported by electronicoxidant and electronic-substrate effect studies.