Kinetics and Mechanism of MnII Catalyzed Periodate Oxidation of O-Anisidine

Author(s): Jaspal Singh, Rajdeep Malik, Om Singh, Sushma and R. D. Kaushik

The kinetics of the periodate oxidation of o-anisidine (ANIS) in acetone-water medium has been followed by monitoring the increase in the absorbance of reaction intermediate, C4, and the main reaction product is methoxy-1, 4-benzoquinone. Results under pseudo first order conditions, [IO4 - ] < < [ANIS], are in agreement with the rate law: d[C]/dt = kK3K4Kw [MnII] [ANIS]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 ANIS. 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: ∆E = 9.95 kJ mol-1, A = 1.18 × 108 dm3 mol-1 s-1; ∆S# = – 99.18 J mol-1 K-1, ∆G# = 38.62 kJ mol-1 and ∆H# = 7.33 kJ mol-1.

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