Kinetics and mechanism of thioether oxidation with H2O2 in the presence of Ti(IV)-substituted heteropolytungstates

✍ Scribed by Oxana A. Kholdeeva; Lyubov A. Kovaleva; Raisa I. Maksimovskaya; Gennadii M. Maksimov

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 184 KB
• Volume: 158
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/s1381-1169(00)00069-8

✦ Synopsis

Ž . Ž . Kinetics of thioether oxidation with concentrated 86% and diluted 35% aqueous H O in the presence of catalytic 2 2 Ž . Äw x 4 Ž . amounts of Bu N PW O Ti OH dimeric heteropolytungstate 1 has been studied in acetonitrile. With 86% H O the 4 7 11 39 2 2 2

reaction was found to be first order in the oxidant, 0.5 order in the catalyst and practically independent on the sulfide concentration and its nature, whereas with 35% H O the reaction was first order in both the catalyst and substrate, the order 2 2 in the oxidant being changed from first to zero with increasing H O concentration. Both 31 P NMR and kinetic data are 2 2 Ž . consistent with mechanism, including fast dissociation of 1 to the monomer 2 , the equilibrium formation of active Ž . hydroperoxo complex PW TiOOH B from 2, and interaction of B with thioether. The rate-limiting steps are the formation 11 of B and the interaction of B with sulfide at low and high H O concentrations, respectively. The kinetic study of 2 Ž . stoichiometric reaction between B, generated in situ from inactive side-on peroxo complex PW TiO A , and thioethers 11 2

Ž . showed first order dependence on both B and sulfide concentration, thus indicating that no binding of thioether to Ti IV occurs. The lack of Hammett-type correlation and specific products obtained in oxidation of benzyl phenyl sulfide allowed to rule out electrophilic oxygen transfer and suggest a mechanism that involves the formation of a thioether cation radical intermediate.