Synthesis of 1,3-dihydroxyacetone via heterogeneous base-free formaldehyde condensation

Abstract

Artificial synthesis of carbohydrates has been a long-standing goal for chemists. The formose reaction is an established non-enzymatic one-step route to monosaccharides from a C1 source, where formaldehyde (HCHO) is polymerized under basic conditions. However, bases can lead to multiple side reactions. Thiazolium salts, when activated by a suitable base, can catalyze HCHO condensation to 1,3-dihydroxyacetone (DHA) via umpolung aldehyde activation, but they can slowly lose their activity due to product adsorption on the active sites. Here, we report a heterogeneous, base-free formaldehyde condensation to DHA using a reactor based on a Soxhlet extractor, which quickly separates the product from the solid catalyst during the reaction. This design not only leads to a stable catalytic operation but also constitutes a clean HCHO-to-DHA conversion system. This oligomerization of formaldehyde to DHA completes a critical step in converting CO₂ to sugar, including CO₂ hydrogenation to methanol (CH₃OH), CH₃OH oxidation to HCHO, HCHO oligomerization to DHA, and DHA condensation to higher carbohydrates.