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Mechanistic studies on the oxidation of some organic sulphides with quinolinium fluorochromate in nonaqueous medium

Meenakshisundaram S., Sathiyendiran V.

Bulletin of the Polish Academy of Sciences. Chemistry

1999

Vol. 47, No. 2

167-174

The oxidation kinetics of diphenyl, dialkyl and methyl phenyl sulphides has been investigated under pseudo-first-order conditions with quinolinium fluorochromate (QFC), a newly developed Cr(VI) reagent in acetonitrile medium. p- Toluene sulphonic acid (TsOH) is used for catalyzing the reaction. Initial-rate methods are used for determining the orders with respect to reactants in dialkyl sulphides. The oxidation is first-order with respect to [QFC] and second-order dependence is observed on [TsOH]. [Sulphide] has no effect on the reaction rate. Diphenyl sulphide (DPS) oxidation follows the rate law, v = k2Rrl [S][Ox][TsOH]. Acrylonitrile retards the rate of oxidation significantly in diphenyl sulphides indicating the involvement of free radical cation sulphur intermediate in the rate-limiting step. The Michaelis-Menten dependence each on [sulphide] and [TsOH] can be well explained by a two-pathway mechanism in methyl phenyl sulphide oxidation. The derived rate law, v = k1[Ox][TsOH] -+ k3[OX][S] is consistent with experimental observations.

Quinolinium fluorochromate oxidation of alpha-hydroxy acids in perchloric acid medium

Meenakshisundaram Subbiah, Sathiyendiran V.

Polish Journal of Chemistry

1998

Vol. 72, nr 10

2261-2266

The kinetics of oxidation of alpha-hydroxy acids (mandelic, lactic and glycolic) with a recently developed new mild Cr(VI) regent quinolinium fluorochromate (QFC) has been investigated in perchloric acid medium. First-order depedence with respect to [oxidant] is observed. Increase in [substrate] increases the rate proportionally. The acidity dependence is fractional order throughout the entire range of acidities studied. Decrease in dielectric constant of the medium increases the oxidation rate considerably. Kinetic solvent isotope effect studies indicate a pre-equilibrium fast proton transfer. Absence of polymerization with acrylonitrile rules out a free radical mechanism. An intermediate formed between protonated oxidant and substrate decomposes in a slow rate-limiting step giving the products.

Kinetics of oxidation of phenoxyacetic acids by quinolinium fluorochromate

Karunakaran K.

Polish Journal of Chemistry

1998

Vol. 72, nr 5

916-924

The kinetics of oxidation of twenty one phenoxyacetic acids by quinolinium fluorochromate have been studied in binary solvent mixtures. Acrylonitrile has no effect on the rates of oxidation in dipolar protic solvent but in a aprotic solvent it decreases the oxidation rates. In both solvent systems there exists an equilibrium prior to the rate limiting step, followed by irreversible decomposition of the complex. The calculated rate constants correlate well with Hammett delta values. Suitable mechanisms have been proposed.