| Summary: | Department of Chemistry, Gurukul Kangri University, Hardwar-249 404, Uttarakhand, India E~mail : rduitkaushik@yahoo.co.in Manuscript received 17 August 2009, revised 30 December 2009, accepted 14 January 2010 The kinetics of the periodate oxidation of 2,4-xylidine (XYL) in acetone-water medium has been followed by monitoring the Increase In the absorbance of reaction intermediate, C 4 , and the main reaction product 3,5-dimethyl-1,2-benzoquinone. Results under pseudo-first order conditions, [IO 4 - ] >> [XYL], are in agreement with the rate law : d(C]/dt = kK 3 K 4 Kw[Mn II ] [S] [IO 4 - ] 0 [H + ]/{K 2 K w + (K w + K b K 2 J[H + ] + K b [H + ] 2 } where kK 3 K 4 is the empirical composite rate constant, K w is ionic product of water, K 2 is acid dissociation constant of H 4 IO 6 - and K b is base dissociation constant of XYL. In agreement with the rate law the 1/k cat versus [H + ] profile passes through the minimum. Free radical scavengers do not affect the reaction rate. The values of thermodynamic parameters are : E a = 4.9 kcal mol -1 , A = 8.7 x 10 3 dml 3 mol -1 s -1 Δ S # = -47.2 cal mol -1 K -1 , Δ G # = 18.9 kcal mol -1 and Δ H # = 4.3 kcal mol -1 .
|
|---|