The oxidation kinetics of reduction intermediate product of methyl red with hydrogen peroxide

The reduction of methyl red and oxidation of intermediate product of its reduction in the presence of molecular oxygen and hydrogen peroxide in 0.2 mol L−1 HAc–NaAc buffer (pH 4.4) were studied at carbon paste electrode by voltammetry. The pseudo-reversible reduction of methyl red in red quinonoid form in a 2e−, 2H+ addition ended to the colorless corresponding hydrazo compound without any following reaction. When dissolved oxygen or hydrogen peroxide were present, the intermediate product of methyl red reduction was oxidized to re-form the original. The apparent rate constant kf of the oxidation reaction of intermediate product by hydrogen peroxide was 744 mol−1 L s−1.