Small gold clusters catalyzing oxidant-free dehydrogenation of glycerol initiated by methene hydrogen atom transfer

Developing oxygen-free methodology for the conversion of alcohols to carbonyls is essentially important because it suppresses the over-oxidation of alcohols to carboxylic acids and enables the production of energetic hydrogen. Here we report a finding of feasible oxidant-free dehydrogenation of glycerol over chemically-pure Au clusters synthesized by a green chemistry method named as laser ablation in liquid (LAL). As results, glycerol is dehydrogenated to form glyceraldehyde which undergoes subsequent dehydrogenation to hydroxymethyl glyoxal. For this, reaction dynamics calculations find interesting dehydrogenation reaction pathways with a low-energy barrier of transition state initiated by hydrogen atom transfer from methene, which differs from the general reaction mechanism based on hydroxyl. Furthermore, it is interesting that the presence of additional -OH group molecules especially H2O can effectively lower the energy barrier in the activation of the O-H and C-H bonds in glycerol. This principle is also applicable to the oxidant-free dehydrogenation of methanol and ethanol, helping to fully understand the catalytic mechanism of alcohols conversion chemistry. (C) 2019 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.