Beta-irradiation of biomass in the presence of 1-alkyl-3-methyl-imidazolium ionic liquids. Identification of an unexpected product from a model compound reaction

Abstract

A combination of swelling in imidazolium ionic liquids and beta-irradiation – both common pretreatments in biomass processing on their own – leads to unexpected effects, with beta-irradiation causing degradation of the pure ionic liquid and also modification of cellulose suspended in the ionic liquid. The underlying chemistry was investigated in a series of model compound experiments. Here, we report that beta-irradiation of the ionic liquid EMIM-OAc containing equimolar amounts of benzaldehyde and d-glucose affords an unexpected condensation product C17H20O7, of which the structure was elucidated as 5-[(1S,2R,3R)-1,2,3,4-tetrahydroxybutyl]-2-phenyl-3-furoic acid, applying a combination of analytical techniques, mainly NMR spectroscopy, after conversion into the ethyl ester derivative for purification. No reaction at all occurred without beta-irradiation under otherwise identical conditions. Intriguingly, the acetate – the IL´s anion – was incorporated into the condensation product, which can formally be regarded as the condensation product of benzoylacetic acid (from benzaldehyde and the IL´s acetate) and d-glucose. The reaction occurred only when all three components – acetate-type IL, glucose and PhCHO – were irradiated simultaneously. The structure elucidation of the compound is presented, along with a discussion of possible formation mechanisms. Future experiments need to address the generality of the reaction for conversion of other aldehydes and aldoses, and the question of whether a similar process occurs with the reducing end of celluloses or other polysaccharides. Graphical Abstract