Glucose oxidation to formic acid and methyl formate in perfect selectivity

Abstract

We report the highly remarkable discovery that glucose oxidation catalysed by polyoxometalates (POMs) in methanolic solution enables formation of formic acid and methyl formate in close to 100% combined selectivity, thus with only negligible sugar oxidation to CO₂. In detail, we report oxidation of a methanolic glucose solution using H₈[PV₅Mo₇O₄₀] (HPA-5) as catalyst at 90 °C and 20 bar O₂ pressure. Experiments with ¹³C-labelled glucose confirm unambiguously that glucose is the only source of the observed formic acid and methyl formate formation under the applied oxidation conditions. Our results demonstrate a very astonishing solvent effect for the POM-catalysed glucose oxidation. In comparison to earlier work, a step-change in product yield and selectivity is achieved by applying an alcoholic reaction medium. The extremely high combined yields of formic acid and methyl formate greatly facilitate product isolation as low-boiling methyl formate (bp = 32 °C) can simply be isolated from the reaction mixture by distillation.