Studies on Manganese (II) Catalyzed Oxidation of N-Methylaniline by Periodate Ion

Author(s): R. D. Kaushik, Manmeet Kaur, Rajdeep Malik and Anuj Kumar

The kinetics of the periodate oxidation of N-methylaniline (NMA) in acetone-water medium has been followed by monitoring the increase in the absorbance of reaction intermediate, C4, and the main reaction product is p-benzoquinone. Results under pseudo first order conditions, [IO4 -] >> [NMA], are in agreement with the rate law:

d[C]/dt = kK3K4Kw[MnII] [S] [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 –, Kb is base dissociation constant of NMA i.e. Substrate [S] and [IO4 –]0 represents the concentration of periodate that has been taken in excess in most of the kinetic runs. 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. Thermodynamic parameters evaluated are: Ea = 5.2 kcal mol-1, A = 4.79 × 109 dm3 mol-1 s-1; ΔS# = – 16.3 cal mol-1, ΔG# = 9.7 kcal mol-1 and ΔH# = 4.6 kcal mol-1.

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