Ru(III)-catalysed oxidation of some amines by chloramine-T in hydrochloric acid medium: Mechanistic aspects and kinetic modeling

Abstract

The kinetics of oxidation of five amines viz., ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), aminoethylpiperazine (AEP) and isophoronediamine (IPDA) by sodium N-chloro- p-toluenesulfonamide or chloramine-T (CAT) in the presence of HCl and Ru(III) chloride was studied at 303 K. The five reactions followed identical kinetics and the experimental rate law is rate = k [ CAT ] 0 [ amine ] 0 x [ H + ] y [ Ru ( III ) ] z , where x, y and z are fractions. A variation of the ionic strength or dielectric constant of the medium and the addition of halide ions and p-toluenesulfonamide had no significant effect on the rate of the reaction. The solvent isotope effect has been studied in D 2O medium. The activation parameters have been evaluated from the Arrhenius plots. Under comparable experimental conditions, the rate of oxidation of amines increases in the order: AEP > TETA > DETA > EDA > IPDA. An isokinetic relationship is observed with β = 377 K, indicating enthalpy as a controlling factor. Oxidation products were identified. C H 3 C 6 H 4 S O 2 N + H 2 Cl of the oxidant has been postulated as the reactive oxidizing species. Further, the kinetics of Ru(III)-catalysed oxidation of these amines have been compared with unanalyzed reactions (in the absence of Ru(III) catalyst) and found that the catalysed reactions are 2–3-fold faster. The catalytic constant ( K C) was also calculated for each amine at different temperatures from the plots of log K C against 1/ T, values of activation parameters with respect to the catalyst have been evaluated. The observed results have also been explained by a plausible mechanism and the related rate law has been deduced.