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MnII Catalyzed Periodate Oxidation of N, N-Diethyl-m-Toluidine : A Kinetic and Mechanistic Study

600-610

One mol of N, N-diethyl-m-toluidine (DET) reacts with two moles of periodate during the initial part of reaction. The main reaction product is 4-methyl-1, 2-benzoquinone. The kinetics of the MnII catalyzed periodate oxidation of DET in acetone-water medium has been followed by monitoring the increase in the absorbance of reaction intermediate. The reaction is first order in reactants and catalyst each. A decrease in dielectric constant of the medium results in decrease in the rate of reaction. Free radical scavengers do not affect the reaction rate. The values of thermodynamic parameters are: ∆E = 24.85 kJ mol-1, A = 1.25 × 1010 dm3 mol-1 s-1; ∆S# = – 142.97 J mol-1 K-1, ∆G# = 67.53 kJ mol-1 and ∆H# = 22.41 kJ mol-1. Under pseudo first order conditions, [IO4 - ] >> [DET], the rate law is given by – 1/kcat = (K2 / kK3K4 [H+ ]) + {(Kw+ KbK2) / kK3K4Kw} + Kb[H+ ] / kK3K4Kw 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 DET. In agreement with the rate law the 1/kcat versus [H+ ] plot passes through the minimum. Detailed molecular mechanism is given.