Direct conversion of C6 sugars to methyl glycerate and glycolate in methanol

Abstract

The present work deals with the one-pot conversion of C6 sugars to methyl glycerate and glycolate via a cascade of retro-aldol condensation and oxidation processes catalyzed by using MoO₃ as the Lewis acid catalyst and Au/TiO₂ as the oxidation catalyst in methanol. Methyl glycerate (MGLY) is the product of C6 ketose (fructose), while methyl glycolate (MG) is produced from C6 aldose (mannose, glucose). It is found that a good one-pot match between two reactive processes is the key to the production of MGLY and MG with high yield (27.6% MGLY and 39.2% MG). A separated retro-aldol condensation and oxidation process greatly decreases their yields, and even no MGLY can be obtained in this separated process. We attribute this to high instability of glyceraldehyde/glycolaldehyde and their different reaction pathways which mainly depend on whether acetalization of retro-aldol products (glyceraldehyde and glycolaldehyde) occurs with methanol or not. This result opens a new prospect on the accumulation of C3 products other than lactate from biomass-derived carbohydrates.