Mechanistic study on the oxidation of (phenylthio)acetic acids by oxo(salen)manganese(V) complexes and the reactivity–selectivity principle
✍ Scribed by Arunachalam Chellamani; Paramasivan Sengu
- Publisher
- Elsevier Science
- Year
- 2008
- Tongue
- English
- Weight
- 427 KB
- Volume
- 283
- Category
- Article
- ISSN
- 1381-1169
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✦ Synopsis
A systematic study on the kinetics and mechanism of oxidation of several (para-substituted phenylthio)acetic acids with various substituted oxo(salen)manganese(V) complexes in acetonitrile at 20 • C is presented. The kinetic data indicate that the reaction is second-order overall, firstorder each in (phenylthio)acetic acid and oxo(salen)manganese(V) complex. Rate studies with substituted (phenylthio)acetic acids give an excellent Hammett correlation with σ + /σ -constants and the ρ-values are in the range of -0.82 to -1.17 for different oxo(salen)manganese(V) complexes. The log k 2 values observed in the oxidation of each (phenylthio)acetic acid by substituted oxo(salen)manganese(V) complexes correlate with 2σ, giving ρ-values from 0.26 to 0.56. A mechanism involving single electron transfer from the sulfur center of the substrate to the oxo complex in the rate-controlling step is envisaged. Kinetic data were obtained over a temperature range of 15-35 • C and the activation parameters evaluated. Correlation analyses show the presence of an inverse relationship between reactivity and selectivity in the reactions of various (phenylthio)acetic acids with a given oxo(salen)manganese(V) complex and also in various oxo(salen)manganese(V) complexes with a given (phenylthio)acetic acid. Mathematical treatment of the results shows the operation of a valid reactivity-selectivity principle in this redox system.