Ionic Liquids as Tools for the Acid-Catalyzed Hydrolysis/Dehydration of Saccharides to Furanic Aldehydes

One of the measures associated with the socio-political and environmental protection policies towards sustainability is the use of biomass as a renewable source of energy, fuels, and chemical products. The chemical valorization of carbohydrate biomass, in particular, the acid-catalyzed conversion of saccharides into the furanic aldehydes, furfural and 5-hydroxymethyl-2-furfuraldehyde, has been a matter of intensive research. These products possess wide application profiles in different sectors of the chemical industry and are thus considered as important platform chemicals. High expectations have been put on the use of ionic liquids (ILs) as tools for these reaction systems, partly due to the singular solubilizing properties of ILs for polysaccharides (important for process intensification), leading to favorable effects when coupled with different types of acid catalysts or when the actual IL is functionalized with acid groups, allowing it to play a dual solvent-acid role. An assessment of the present state-of-the art on this topic is made in this review, showing that promising results have been reported using mild reaction conditions.