Picolinic acid promoted oxidative decarboxylation of phenylsulfinylacetic acid by Cr(VI)
The kinetics and mechanism of picolinic acid promoted reaction of phenylsulfinylacetic acid (PSAA) with Cr(VI) was carried out in aqueous acetonitrile medium under pseudo first order conditions. The reaction follows Michaelis-Menten type of kinetics with respect to PSAA. The catalytic activity by picolinic acid can be interpreted on the basis of the formation of a highly active oxidizing species, Cr(VI)-PA complex. The mechanism involves the formation of a termolecular complex, Cr(VI)-PA-PSAA by the nucleophilic attack of the sulfur atom of PSAA on chromium of Cr(VI)-PA complex in an equilibrium step followed by ligand coupling in a slow step. Electron releasing substituents in the phenyl ring of PSAA accelerate while electron withdrawing groups retard the reaction rate. The overall rate constants for the para- and meta-substituted PSAAs are found to correlate excellently with Hammett σ constants with a very low reaction constant, ρ.
KEY WORDS: Phenylsulfinylacetic acid, Cr(VI), Picolinic acid, Oxidative decarboxylation, Substituent effect, Catalysis
Bull. Chem. Soc. Ethiop. 2016, 30(1), 137-146.