Sono-photolysis of phenylglyoxylic acid and stability studies of d,l-2,3-diphenyltartaric acid

Photodecarboxylation and photoreduction of phenylglyoxylic acid as well as the influence of ultrasound on these reactions were studied. Ultrasound considerably enhanced photodecarboxylation of phenylglyoxylic acid in acetonitrile with low content of water (CH3CN–H2O, 0.5%, v/v). No ultrasound effect was observed at higher content of water. Photoreduction of phenylglyoxylic acid resulted in formation of isomers of 2,3-diphenyltartaric acid. We found out that photosonication had no influence on the rate of formation of 2,3-diphenyltartaric acids but affected only the ratio of d,l and meso isomers of this acid. The thermal instability of 2,3-diphenyltartaric acids can affect the course of photoreduction of phenylglyoxylic acid. Phenylglyoxylic and benzoic acids were the main products after the thermal decomposition of d,l-2,3-diphenyltartaric acid in 2-propanol. The rate of decomposition of d,l-2,3-diphenyltartaric acid was very sensitive to its concentration, temperature and a presence of oxygen as well as water in the reaction mixture. Sonication caused a large decrease of the rate of decomposition of d,l-2,3-diphenyltartaric acid.