Kinetics and Mechanism of Oxidation of m-Anisidine by Periodate Ion

Abstract

The kinetics of the oxidation of m-anisidine (MMA) by periodate ion 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. The rate of reaction decreases with decrease in dielectric constant of the medium. Free radical scavengers do not affect the reaction rate. The stoichiometry has been found to be 1 mol MMA:2 mol of periodate. Thermodynamic parameters evaluated are: E_a = 8.8 kcal mol^-1, A = 3.4.2 × 10⁴ dm³ mol^-1 s^-1; ΔS^# = - 39.9 kcal mol^-1, ΔG^# = 20.8 kcal mol^-1 and ΔH^# = 8.2 kcal mol^-1. Results under pseudo first order conditions, [m-anisidine] >> [IO₄ ^–], are in agreement with the rate law:

d[C]/dt = kKK_w [S]₀[IO₄ ^–][H⁺] /{K₂ K_w + (K_w + K_b K₂) [H⁺] + K_b [H⁺]²}

where kK is the empirical composite rate constant, K_w is ionic product of water, K₂ is acid dissociation constant of H₄IO₆^–, K_b is base dissociation constant of MMA and [S]₀ represents the concentration of MMA that has been taken in excess. In agreement with the rate law the 1/k₂ versus [H⁺] profile passes through the minimum. Main reaction product isolated and characterized is methoxy-1,4-benzoquinone.