The kinetics of oxidation of Toluidine blue (hereafter referred to as TB+) by nitrite ion have been studied in aqueous acidic medium under the pseudo-first order condition of excess [NO2 -] at 25 ±1°C, [H+] = 1 x 10-2 mol dm-3 and ionic strength, I = 0.50 mol dm-3 (NaCl). The stoichiometry of the reaction was observed to be 3:1 mole ratio of toluidine blue to nitrite ions. The redox reaction follows second order kinetics at constant hydrogen ion concentration and the rate also shows first order dependence on hydrogen ion concentration. The overall reaction conforms to the rate law: d[TB+] dt = a [TB+ ][NO2 - ][H+ ] Where a = 40.76 dm6 mol-2 s-1 A plausible mechanism has been proposed for this reaction.
