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

The oxidation of organic sulfoxides to sulfones with sodium hypochlorite catalyzed by (salen)Mn-III complexes in 90% acetonitrile-10% water (v/v) follows an overall second-order kinetics, first-order each in the oxo complex and the substrate. The less nucleophilic sulfoxides are more sensitive to substitutent effect (rho=-2.57) compared to the corresponding sulfides (rho=-1.85). A positive rho-value (rho=0.50) is observed in the oxidation of phenyl methyl sulfoxide by substituted oxo(salen)manganese(V) complexes. Substituent, acid and solvent effect studies reveal the operation of a common S(N)2 mechanism. Correlation analyses establish that there is an inverse relationship between reactivity and selectivity in both the sulfoxide and complex series. A valid reactivity-selectivity principle (RSP) is observed in this redox system. (c) 2005 Elsevier B.V. All rights reserved.