Reduction of 3, 7-Bis(dimethylamino)Phenazothionium Chloride by Benzenethiol inAqueous Nitric Acid Medium: A MechanisticApproach

摘要

The kinetics of the reduction of 3,7-bis(dimethylamino)phenazothionium chloride (MB~(+)) by benzenethiol in aqueous solution has been investigated in the acid range 0.3≤[H~(+) ≤ 0.9 mole dm~(-3), ionic strength 0.4 ≤ μ ≤ 1.0 mole dm~(-3) (NaNO_(3)) and temperature, T = 29oC. The reaction is first order in both [oxidant] and [reductant] and display an inverse order acid dependence with an overall reaction that conforms to the rate law:(-d)/dt [MB~(+)] = (Kk4[H~(+)]-1 + k6)([MB~(+)][ C_(6)H_(5)SH])at [H~(+)] = 0.3 mole dm~(-3) and μ = 1.0 mole dm-3 (NaNO_(3)). The rate of the reaction increased with increase in the ionic strength of the reaction medium and also with the decrease in dielectric constant. Added HCOO- and Cl- enhanced the rate of the reaction. Spectroscopic investigation did not reveal the formation of any stable reaction intermediate. Test for free radical was positive and a plausible mechanism consistent with these observations has been proposed.