A combined computational and experimental approach to revisit the Butlerov reaction

The Butlerov, or formose, reaction is the transformation of formaldehyde into a complex mixture of sugars in the presence of calcium hydroxide, eventually leading to sugar degradation with the formation of a tar, difficult to analyse. Its intricate mechanism has long captivated researchers, not only for its potential in sugar synthesis for food applications but also for its relevance to prebiotic chemistry. The autocatalytic formation of glycolaldehyde from the retro-aldol reaction of tetroses was proposed by Breslow in 1959 and has been discussed in most of the literature; however, the mechanism has recently been set under discussion. This study aims to explore the reaction pathway by starting from the first-principles automatic generation of reaction products and density functional theory (DFT) free energy calculations. The kinetics of the obtained chemical network were simulated and compared with experimental results. No derivatizing agents were employed for sugar identification to avoid biased detection based on their reactivity. Our results are in accordance with recent literature showing that C7 branched ketoses are formed mainly and, in addition, that the autocatalytic mechanism is not needed to explain the results. The model was also tested by using different sugars as initiators, showing agreement with published data.