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The kinetics and mechanism of the uncatalyzed and Ru(III)-catalyzed oxidation of methylene violet (3-amino-7-diethylamino-5-phenyl phenazinium chloride) (MV + ) by acidic chlorite is reported. With excess concentrations of other reactants, both uncatalyzed and catalyzed reactions had pseudo-first-order kinetics with respect to MV + . The uncatalyzed reaction had first-order dependence on chlorite and H + concentrations, but the catalyzed reaction had first-order dependence on both chlorite and catalyst, and a fractional order with respect to [H + ]. The rate coefficient of the uncatalyzed reaction is (5.72 ± 0.19) M −2 s −1 , while the catalytic constant for the catalyzed reaction is (22.4 ± 0.3) × 10 3 M −1 s −1 . The basic stoichiometric equation is as follows: 2MV + + 7ClO 2 − + 2H + = 2P + CH 3 COOH + 4ClO 2 + 3Cl − , where P + = 3-amino-7-ethylamino-5-phenyl phenazinium-10-N-oxide. Stoichiometry is dependent on the initial concentration of chlorite present. Consistent with the experimental results, pertinent mechanisms are proposed. The proposed 15-step mechanism is simulated using literature; experimental and estimated rate coefficients and the simulated plots agreed well with the experimental curves.

Safranine-O, a dye of the phenazinium class, was found to exhibit intricate kinetics during its reaction with bromate at low pH conditions. Under conditions of excess concentrations of acid and bromate, safranine-O (SA + ) initially depleted very slowly (k = (3.9 ± 0.3) × 10 −4 M −3 s −1 ) but after an induction time, the reaction occurred swiftly. Bromide exhibited a dual role in the reaction mechanism, both as an autocatalyst and as an inhibitor. The added bromide increased the initial rate of depletion of SA + , but delayed the transition to rapid reaction. The overall stiochiometric reaction was found to be 6SA + + 4 BrO 3 − = 6SP + 3N 2 O + 3H 2 O + 6H + + 4Br − , where SP is 3-amino-7-oxo-2,8-dimethyl-5-phenylphenazine. The fast kinetics of the reaction between aqueous bromine and safranine-O (k = (2.2 ± 0.1) × 10 3 M −1 s −1 ) are also reported in this paper A 17-step mechanism, consistent with the overall reaction dynamics and supported by simulations, is proposed and the role of various bromo and oxybromo species is also discussed.

Methylene violet (MV(+)), a phenazine class of dye during oxidation by the bromate ion under acidic conditions, exhibited complex nonlinear behavior. The intricate kinetics of reaction of methylene violet [3-amino-7-(diethyleamino)-5-phenyl phenazium chloride, MV(+)] with acidic bromate was investigated using the stopped flow technique. Under excess acid and bromate concentration conditions, MV(+) exhibited a very slow reaction initially but a very rapid reaction after an induction time. The reaction had first-order dependence on both H(+) and BrO(3)(-) ions. The overall stoichiometric reaction is 2 MV(+) + 2 BrO(3)(-) + H(2)O --> 2 MP + 2 HON(CH(2)CH(3))(2) + N(2)O + 2 H(+) + 2 Br(-) where MP is the 3,7-dioxo-5-phenyl phenazine. The active roles of various bromo and oxybromo species in the mechanism are discussed. The rapid kinetics of the direct reaction of bromine with MV(+) is also reported. A 19-step mechanism, consistent with the experimental data and validated by simulations using Simkine-2, is proposed.

ABSTRACT. 'Simkine3', a Delphi based software is developed to simulate the kinetic schemes of complex reaction mechanisms involving multiple sequential and competitive elementary steps for homogeneous and heterogeneous chemical reactions. Simkine3 is designed to translate the user specified mechanism into chemical first-order differential equations (ODEs) and optimise the estimated rate constants in such a way that simulated curves match the experimental kinetic profiles. TLSoda which uses backward differentiation method is utilised to solve resulting ODEs and Downhill Simplex method is used to optimise the estimated rate constants in a robotic way. An online help file is developed using HelpScrible Demo to guide the users of Simkine3. The versatility of the software is demonstrated by simulating the complex reaction between methylene violet and acidic bromate, a reaction which exhibits complex nonlinear kinetics. The new software is validated after testing it on a 19-step intricate mechanism involving 15 different species. The kinetic profiles of multiple simulated curves, illustrating the effect of initial concentrations of bromate, and bromide were matched with the corresponding experimental curves.