Kinetics and Mechanism of Periodate Oxidation of N,N-Dimethylaniline and N,N-Diethylaniline

Abstract

The reaction was found to be second order being first order in each reactant i.e., N,Ndimethylaniline (DMA) or N,N-diethylaniline (DEA) and the oxidant, periodate. The kinetics of the reaction has been followed by monitoring the increase in the absorbance of reaction intermediate, C. The rate law in accordance with the results under pseudo first order conditions, [IO₄^–] >> [DMA or DEA], is given by: d[C]/dt = kKK_w [S] [IO₄^–]₀ [H⁺]/{K₂K_w + (K_w + K_bK₂) [H⁺] + K_b[H⁺]₂}, where kK = empirical composite rate constant, Kw is ionic product of water, K₂ is acid dissociation constant of H₄IO₆^–, Kb is base dissociation constant of aniline taken and [IIO₄^–]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 (where k₂ is second order rate constant). The rate of reaction remains unaffected by free radical scavengers and increases with increase in dielectric constant of the medium. Thermodynamic parameters evaluated are: E_a = 13.2 kcal mol^-1, A = 5.89 × 10⁹ dm³ mol^-1 s^-1; DS# = -16.2 cal mol^-1 K^-1, DG# = 17.6 kcal mol^-1 and DH# = 12.6 kcal mol^-1 for DEA oxidation and E_a = 16.1 kcal mol^-1, A = 1.06 × 10¹² dm³ mol^-1 s^-1; DS# = -6.32 cal mol^-1 K^-1, DG# = 17.4 kcal mol^-1 and DH# = 15.5 kcal mol^-1 for DMA oxidation. Main reaction products of the periodate oxidation of DEA are O-ethylquinoneoxime and p-nitro-sophenetole while these are O-methylquinoneoxime and p-nitrosoanisole for DMA oxidation.