Uncatalyzed and ruthenium(III)‐catalyzed reaction of acidic chlorite with methylene violet

Abstract

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.

Aquachlororuthenium(III) catalysis in the oxidation of substituted 4-oxo-4-arylbutanoic acids by bromate in acid medium: a kinetic and mechanistic study and validity of linear free-energy relationships

“…However, the present reaction does not show any induction period over a wide concentration range of bromate, Ru(III), oxo acid and H 2 SO 4 . The kinetic behavior of the present reactants and catalyst is entirely different from the earlier reports of Ru(III)-catalyzed oxidation reactions [6][7][8][9][10][11]. The mechanism neither resembles catalysis by bromide anions [12] nor that of Ru(III)-catalyzed oxidation of organic substrates with the oxidants [6][7][8][9][10][11].…”

“…Though bromate itself is a strong oxidizing agent, having a redox potential of 1.45 V [5], the oxidations generally require a catalyst. Ru(III) has been used as a homogeneous catalyst in many redox reactions and its versatility as a catalyst is revealed by oxidation studies of various organic substrates involving different oxidants [6][7][8][9][10]. The mechanism of catalysis is often quite complicated due to the formation of different intermediate complexes, free radicals and oxidation states of Ru.…”

Aquachlororuthenium(III) complex catalysis in the oxidation of malonic and methylmalonic acids by bromate in perchloric acid medium. Study of induction period and evaluation of individual kinetic parameters

“…Also in Ru III -catalyzed acidic chlorite oxidation of methylene violet [4]. Although, Ru(V) oxo complexes are rare, few were isolated and characterized [41].…”

“…The most frequently used ruthenium catalyst is the ruthenium(III) chloride hydrate, a non-toxic and homogenous catalyst. Many kinetic studies have been undertaken using this catalyst [1][2][3][4][5][6][7][8][9][10], but very few studies are available in acid media. Ruthenium(III) catalysis in redox reactions involves different degrees of complexity, due to the formation of different intermediate complexes, free radicals and to different oxidation states of ruthenium.…”

Kinetics and mechanism of the oxidation of Coomassie Brilliant Blue-R dye by hypochlorite and role of acid therein

“…10 We have also reported the oxidation kinetics and mechanisms of reactions of triaryl 11,12 (aniline blue and thymol blue), phenothiazine 13 (methylene blue) and heterocyclic 14,15 (acridine orange and safranine-o) dyes with acidic bromate as oxidant. We also investigated the oxidative degradation kinetics of indigo carmine with hypochlorite 16 and the reaction kinetics of triaryl 17 (methylene violet), benzophenoxazines 18 (Nile blue and Meldola's blue) and phenothiazine 19 (toluidine blue) dyes with chlorite under low pH conditions. More recently, we investigated and reported the kinetics and mechanism of oxidation of the toxic dye, amaranth, by hypochlorite and hypochlorous acid under varied pH conditions.…”