Catalytic transformations of cellulose and its derived carbohydrates into 5-hydroxymethylfurfural, levulinic acid, and lactic acid

The catalytic transformation of cellulose into key building-block or platform chemicals such as 5-hydoxymethylfurfural (HMF), levulinic acid, and lactic acid under mild conditions, has attracted much attention in recent years, as these conversions can be operated without consumption of hydrogen or oxygen and thus are more economical compared to the hydrogenolysis or oxidation of cellulose. This review article highlights recent advances in the development of novel catalysts or catalytic processes for the conversion of cellulose and its derived carbohydrates into HMF, levulinic acid, and lactic acid or their esters under inert atmosphere. We also analyze efficient catalytic systems for HMF production, in particular Lewis acids combined with ionic liquid or biphasic systems. For the formations of levulinic and lactic acids or their esters, we focus on the reactions in aqueous and alcohol media catalyzed by multifunctional catalysts that combine the functions of hydrolysis, isomerization, and dehydration-rehydration or retro-aldol reactions. The reaction mechanism for each process will also be discussed to gain insights into the activation of C-O and C-C bonds in the absence of hydrogen or oxygen.