Kinetics and Mechanism of Periodate Oxidation of N,N-Diethyl-m-toluidine in Acetone-Water Medium

Abstract

Main reaction product of the periodate oxidation of N,N-diethyl-m-toluidine (DET) in acetonewater medium is methyl-1,4-benzoquinone. It was isolated and characterized. The kinetics of the reaction has been followed by monitoring the increase in the absorbance of reaction intermediate, C. The reaction followed second order behaviour, being first order in each reactant. Results under pseudo first order conditions, [IO₄^–] >> [DET], are in agreement with the rate law: d[C]/dt = kKK_w [S] [IO₄^–]₀[H⁺]/{K₂K_w + (K_w + K_bK₂)[H⁺] + Kb[H⁺]₂}, where kK 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 DET and [IO₄^–]0 represents the concentration of periodate that has been taken in excess. In agreement with the rate law the 1/k₂ versus [H⁺] profile passes through the minimum. Increase in ionic strength increases the rate of reaction. Further, the rate of reaction increases with increase in dielectric constant of the medium. Free radical scavengers do not affect the reaction rate. Thermodynamic parameters evaluated are: DE = 23.2 kJ mol^-1, A = 2208.6 dm³ mol^-1 s^-1; DS# = -190.0 J mol^-1 K^-1, DG# = 79.5 kJ mol^-1 and DH# = 20.92 kJ mol^-1.