Oxidant-Free Transformation of Ethylene Glycol toward Glycolic Acid in Water

Abstract

Full utilization of oxygen in biomass can greatly improve its atomic efficiency because of its nature of containing 40%–45% oxygen. In this work, we achieved a complete conversion of ethylene glycol toward glycolic acid with accompanying evolution of hydrogen via a cascade dehydrogenation and Cannizzaro reaction in water without any external oxidant. The yield of glycolic acid can reach 81%, and the whole homogeneous catalytic system displays a long-term continuous reaction stability. Moreover, this dehydrogenative oxidation process can be applied into the one-pot conversion of biomass carbohydrates toward α-hydroxyl acid. This finding provides a closer insight into the application of catalytic dehydrogenative oxidation techniques in designing value-added products from biomass-derived compounds as well as hydrogen evolution as a byproduct.

Manganese-Catalyzed Reformation of Vicinal Glycols to α-Hydroxy Carboxylic Acids with the Liberation of Hydrogen Gas

“…However, selective dehydrogenation of 1,2-diols suppressing over-oxidation, self-condensation, and polymerization is highly challenging . Additionally, the acceptorless liberation of hydrogen gas is a concern, and a sacrificial hydrogen acceptor is often required for successful catalysis. − The reformation reaction is only studied for the simplest ethylene glycol molecule using precious ruthenium, and platinum metal-derived catalysts by Grützmacher, Milstein, and others (Scheme B). − This too suffers from poor selectivity and reactivity. , While this work is in progress, Xu and Tu elegantly disclosed an iridium-catalyzed transformation of vicinal glycols to α-hydroxy acetates in the presence of oxygen as the terminal hydrogen acceptor . A general synthesis of α-hydroxy acids from readily available glycols utilizing non-noble metal catalysts without the need for an acceptor with high yield and selectivity is the need of the hour.…”

Synthesis of α-Hydroxy Acids via Dehydrogenative Cross-Coupling of a Sustainable C2 Chemical (Ethylene Glycol) with Alcohols

“…The development of sustainable and carbon-neutral catalytic processes that use biomass-derived feedstocks is critical to maintain the current size of production and consumption of chemicals without increasing carbon emission. − Sustainable processes include transition metal-catalyzed valorization of biomass resources to produce industrially useful α-hydroxy acids (AHAs). − Commonly used AHAs, glycolic acid (C 2 AHA), and lactic acid (C 3 AHA) have been produced by bacteria-mediated fermentation or the chemical process. − Sustainable carbohydrate feedstocks have also been employed to obtain glycolic acid and lactic acid via metal-catalyzed C–C bond cleavage. , In addition, an Ir-catalyzed synthesis of lactic acid from ethylene glycol and methanol was recently reported . Sn-catalyzed cleavage of glucose and Sn-catalyzed cross-coupling of 1,3-dihydroxyacetone and formaldehyde were used in the synthesis of methyl-4-methoxy-2-hydroxybutanoate and α-hydroxy-γ-butyrolactone (C 4 AHAs), respectively.…”

Homogeneous Reforming of Aqueous Ethylene Glycol to Glycolic Acid and Pure Hydrogen Catalyzed by Pincer‐Ruthenium Complexes Capable of Metal–Ligand Cooperation

“…The group of Grützmacher reported the oxidative dehydrogenation of alcohols and polyalcohols, including ethylene glycol, to carboxylic acids using a homogeneous rhodium catalyst under mild conditions, albeit in the presence of sacrificial hydrogen acceptors such as ketones or methyl methacrylate [16] . Reforming of ethylene glycol to glycolic acid homogeneously catalyzed by an iridium complex (4 mol %) was reported recently, although the catalytic mechanism was not studied [17] . Very recently, homogeneous iridium‐catalyzed dehydrogenative cross‐coupling of ethylene glycol and methanol to lactic acid was also disclosed by Tu, Xu and co‐workers [18] .…”