The oxidation of gluconic acid by chromium(VI) in perchloric acid has been found to follow the rate law: −d[CrVI]/dt = (k′1 + k′2[GA])[H+]2[CrVI], where k′1 = (7.1 ± 0.2) × 10−4 M−2 s−1 and k′2 = (9.4 ± 0.2) × 10−2 M−3 s−1. This rate law corresponds to the reaction leading to the formation of 2-ketogluconic acid by C—H cleavage when a 20-fold or higher excess of acid over chromium(VI) is employed. Buildup and decay of chromium(V) intermediates accompany the decay of chromium(VI). Chromium(V) rates of decay are similar or slower than those of chromium(VI), as observed by electron paramagnetic resonance (epr) and visible spectrophotometry.

Detection of reaction intermediates is an important matter when a kinetic experiment is carried out, to reinforce the mechanism derived from the rate law. However, this task may be difficult when the transient species are very short-lived, and under kinetic conditions they may not be observed. If this is so, conditions under which detection would be feasible will have to be found out, and students should be taught to do it.Herein oxidations of organic substrates by potassium dichromate in aqueous solution have been chosen as model systems, since both Crv and Crvl complexes involved in these reactions (1) may be detected easily. When CrVI is mixed with biologically related molecules in aqueous solution, growth and decay of CrVI and Crv intermediates are observed, with "stability" ascribed to complex formation with substrate (2). Besides, stable Crv compounds with ahydroxy-acids having a tertiary alcohol group have been isolated and characterized (3). Identification of Crv intermediates has led to the consideration that such species may be involved in the molecular processes leading to the onset of cancer formation, and they are likely candidates

Oxidation of D-Gluconic Acid by Chromium(VI) in Perchloric Acid-(first kinetic study on the oxidation of a polyhydroxycarboxylic acid). -(SIGNORELLA, S. R.; SANTORO, M. I.; MULERO, M. N.; SALA, L. F.; Can.