Kinetic and mechanistic aspects for the tartaric acid oxidation by vanadium(V) in sulfuric acid medium

Abstract

Tartaric acid oxidation by vanadium(V) in sulfuric acid medium was investigated spectrophotometrically at 760 nm and 30ЊC by appearance of the vanadium(IV), as vanadyl. The reaction rate was determined under pseudo-first-order conditions with an excess of hydroxyacid over the oxidant concentration. The oxidation showed a first-order dependence with respect to vanadium(V) concentration and fractional orders with respect to tartaric acid and sulfuric acid concentrations, with no control and with constant ionic strength. The reaction rate is enhanced by an increase of ionic strength, and slightly reduced by a decrease of the dielectric constant of the medium. The activation parameters were calculated based on the rate constants determined in the 293 to 313 K interval. The proposed oxidation mechanisms and the derived rate laws are consistent with the experimental rate laws.

Citric acid oxidation by vanadium(V) in sulfuric acid medium: Kinetic and mechanistic study

“…Meanwhile, the tartaric acid oxidation in sulfuric acid medium presented a first-order dependence with respect to vanadium(V) and fractional orders with respect to tartaric acid and sulfuric acid concentrations, with no control and with constant ionic strength. In this case, a faster rate is observed at a fixed ionic strength [4]. When lactic acid was oxidized in sulfuric acid medium, a faster rate was also observed with ionic strength control, and the plot of ln k obs vs.…”

“…As related previously, we assumed that sulfuric acid behaves as a strong monobasic acid for the purpose of hydrogen and/or bisulfate ions. The oxidation of citric acid, HCi, by vanadium(V) takes place more rapidly in comparison with lactic acid [6], malic acid [5,7], and tartaric acid [4], indicating that electron-withdrawing substituents at the ␣-position increase the oxidation rate. This was experimentally verified through the use of a smaller concentration of sulfuric acid in the kinetic measurements.…”