Features of homogeneous oxidation of glyoxal to glyoxylic acid

Abstract

The values and nature of induction periods (IP) for the oxidation of commercial glyoxal (CG) to glyoxylic acid (GA) by HNO₃—HCl mixtures were studied under diff erent reaction conditions. The physicochemical interpretation of the IP enables one to control the oxidation of CG to target GA. It was established by UV spectroscopy that the addition of HCl favored the disintegration of n-mers of CG and simultaneous accumulation of structures with aldehyde groups (SAG), which are active forms of CG during its oxidation to GA. The rate constants and activation energies of SAG accumulation were determined. The theoretical UV spectra, which are well consistent with the experimental curves, and thermochemistry of equilibria of the CG forms were calculated in the Gaussian/09 program package. The IP values at varied temperature, ratio of CG to hydrochloric acid, and time of storage of the reaction mixture were determined on the Arduino-based unit with a temperature sensor. The IP value is almost halved with an increase in the amount of HCl. The IP is also nearly halved as the time of storage of a CG—HCl mixture increases by three times. The obtained regularities indicate that the character of the IP of CG oxidation is related to the continuous disintegration of n-mers in CG solutions, i.e., to the permanent accumulation of SAG, which are fi nally oxidized to GA.