Selective Oxidation of Glycolaldehyde to Glyoxal Using Ruthenium Complex Catalysts

Cellulose comprises glucose units, and therefore glucose and its derivatives have received attention as a carbon source replacing fossil fuels. In particular, glyoxal, which is obtained from glucose by retro-aldol reaction and subsequent oxidation via glycolaldehyde, is a feedstock for useful chemicals. However, efficient catalytic synthesis of glyoxal from glycolaldehyde has not been reported because the unwanted excessive oxidation of glyoxal occurs. In this study, catalytic synthesis of glyoxal from glycolaldehyde using a ruthenium complex catalyst with a bromophenyl terpyridine ligand was carried out. After optimizing reaction conditions, glyoxal was obtained in a 32% yield in N,N-dimethylformamide at 100°C for 3 h using O₂ gas as an oxidant. Furthermore, the obtained mixture was reacted with sodium sulfite to form precipitates, which are bisulfite adducts. It could be easily separated as a glyoxal equivalent from the catalyst and solvent by filtration. These results indicate that a new method for the synthesis of glyoxal from biomass-derived glycolaldehyde has been achieved.