Selective oxidation of 5-keto-d-gluconate to l-(+)-tartaric acid on transition metal chelate catalyst

•Selectively split of 5-keto-d-gluconate to l-(+)-tartaric acid with cupric ion.•Significantly increase the l-(+)-tartaric acid production rate.•Hypothetically propose the mechanism of 5-keto-d-gluconate oxidation with cupric ion in alkaline buffer.

The selective oxidation of 5-keto-d-gluconate (5-KGA) to l-(+)-tartaric acid (L-TA) was performed under mild conditions in an alkaline carbonate buffer, employing various transition metal catalysts. CuSO4·5H2O was found to be an efficient catalyst, providing a molar conversion rate and selectivity for L-TA of 74. 58% and 76.18%, respectively. Based on an analysis of the reaction process using UV–Vis spectroscopy, coordination number determination and functional group detection, a mechanism for the metal chelate catalytic oxidation of 5-KGA to L-TA is proposed, and this mechanism is shown to be completely different from that associated with catalysis by vanadate.

Graphical abstractThe graphical abstract demonstrates the oxidation reaction of 5-KGA in the carbonate buffer by CuSO4·5HO with the participation of oxygen. The mental-5-KGA-oxygen complex well illustrates the coordination number of mental-5-KGA and the bond orbital of oxygen molecular.Figure optionsDownload full-size imageDownload as PowerPoint slide