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MnII Catalyzed Oxidation of 2,5-Xylidine by Periodate Ion – A Kinetic and Mechanistic Study

Jaspal Singh, RD Kaushik, Om Singh, Richa Saini and Ekata Kumari

The kinetics of the periodate oxidation of 2, 5-Xylidine (2,5-XYL) in acetone-water medium has been followed by monitoring the increase in the absorbance of reaction intermediate, C4, and the main reaction product is 2, 5-dimethyl–1, 4–benzoquinone. Results under pseudo first order conditions, [IO4-] >> [2,5-XYL], are in agreement with the rate law:d[C]/dt = kK3K4Kw [MnII] [2,5-XYL]0 [IO4-]0 [H+] /{K2 Kw + (Kw + Kb K2 )[H+] + Kb [H+]2}. Where kK3K4 is the empirical composite rate constant, Kw is ionic product of water, K2 is acid dissociation constant of H4IO6- and Kb is base dissociation constant of 2,5-XYL. In agreement with the rate law the 1/kcat versus [H+] profile passes through the minimum. Free radical scavengers do not affect the reaction rate. The values of thermodynamic parameters are: ΔE = 5.69 kJ mol-1, A = 6.52 × 106 dm3 mol-1 s-1; ΔS# = –104.44 J mol-1K-1, ΔG# = 35.56 kJ mol-1 and ΔH# = 3.16 kJ mol-1.