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2 Polish Journal of Chemistry

2 1998

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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.

Cooxidation of S-phenylmercaptoacetic acid and oxalic acid with pyridinium chlorochromate

Mangalam G., Meenakshisundaram Subbiah

Polish Journal of Chemistry

1998

Vol. 72, nr 3

582-586

The kinetics of oxidation of the mixture of S-phenylmercaptoacetic acid (PMA) and oxalic acid with pyridinium chlorochromate (PCC) in 30% (v/v) acetic acid-water exhibits a first-order dependence each in [PCC] and [PMA], at low concentrations of the latter. At high concentration of the substrate, a fractional order in [PMA] is observed. The rate increases linearly with [oxalic acid]. Increased reactivity in the presence of oxalic acid with carbon dioxide as one of the products is well explained by Rocek's mechanism for cooxidation, involving a ternary complex. Formation of a ternary complex at low concentrations and decomposition of the complex at higher concentrations of PMA is considered to be the respective rate-limiting step.