Manganese(catalyzed oxidation of 2,4-xylidine by periodate - A kinetic-mechanisc study

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, C₄, and the main reaction product 3,5-dimethyl-1,2-benzoquinone. Results under pseudo-first order conditions, [IO₄^-] >> [XYL], are in agreement with the rate law :

d(C]/dt = kK₃K₄Kw[Mn^II ] [S] [IO₄^-]₀ [H⁺]/{K₂K_w + (K_w + K_bK₂J[H⁺] + K_b[H⁺]₂}

where kK₃K₄ is the empirical composite rate constant, K_w is ionic product of water, K₂ is acid dissociation constant of H₄IO₆^- 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 10³ dml³ mol^-1 s^-1; ΔS# = -47.2 cal mol^-1 K^-1, ΔG^# = 18.9 kcal mol^-1 and ΔH^# = 4.3 kcal mol^-1.