Linear free energy relationship in complex reaction: Tungsten(VI) catalyzed perborate oxidation of S-Phenylmercaptoacetic acids

✍ Scribed by C. Karunakaran; V. Ramachandran; P. N. Palanisamy

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 137 KB
• Volume: 31
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/(sici)1097-4601(1999)31:9<675::aid-kin8>3.0.co;2-h

✦ Synopsis

Tungsten(VI) catalyzes perborate oxidation of S-phenylmercaptoacetic acid. The catalyzed oxidation is first order with respect to the oxidant, independent of [H ϩ ], and displays Michaelis-Menten dependence on [PhSCH 2 COOH] and [W(VI)]. The reaction requires time for equilibration between the oxidant and the catalyst. Oxodiperoxotungsten(VI) (WO(O 2 ) 2 ) is the probable oxidizing species, and decomposition of PhSCH 2 COOHϪWO(O 2 ) 2 complex is rate limiting. At low [PhSCH 2 COOH] and fixed [W(VI)], the oxidation follows a second order rate law. Operation of the linear free energy relationship in the oxidation has been tested with a few electron withdrawing and a few electron donating substituents. At high temperature, electron-withdrawing groups decelerate and electron releasing groups accelerate the oxidation, the variation in rate with the substituent is in conformity with the Hammett equation. But at low temperature, electron donating substituents fail to accelerate the oxidation. The results are rationalized.