Efficient conversion of glucose to HMF using organocatalysts with dual acidic and basic functionalities - A mechanistic and experimental study

Glucose conversion to 5-hydroxymethyl furfural (HMF) was carried out using either amino (basic), sulfonic acid (Bronsted acidic) or both the functionalities containing organocatalysts. Sulfanilic acid with both the functionalities, was found to be a promising multifunctional catalyst yielding 44% HMF. Glucose to HMF is a two-step reaction pathway comprising of (i) glucose isomerization to fructose under basic conditions (ii) fructose dehydration to HMF under acidic conditions. The overall detailed reaction mechanism was studied using density functional theory (DFT). The transformation of open chain glucose to ene-diol intermediate through Lobry de Bruyn-van Ekenstein rearrangement was found to be the rate limiting step with highest energy barrier of 25.2 kcal/mol during glucose isomerization to fructose. The heats of the reactions of two exothermic reactions namely glucose isomerization to fructose and fructose dehydration to HMF are 3.7 kcal/mol and 33.1 kcal/mol respectively.