β-Irradiation in the presence of 1,3-dialkylimidazolium ionic liquids causes covalent cellulose derivatization with simultaneous nitrogen incorporation

Abstract1-Alkyl-3-methylimidazolium ionic liquids are common cellulose solvents and biomass pretreatment agents, while beta-irradiation (“e-beaming”) is often used to decrease the recalcitrance of biomass towards hydrolysis or saccharification. Aiming at the general goal of elucidating the interaction between lignocellulosics, imidazolium-based ionic liquids, and beta-irradiation, we studied the effect of beta-irradiation on the pure ILs 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium, both as chloride and acetate. Contrary to the expectation of inertness, irradiation caused degradation of the ILs, which was proportional to irradiation dosage, i.e., to irradiation time and intensity. At a dosage of 2400 kGy, 0.2% (2000 ppm) of the IL were chemically altered. The main degradation pathway is the formation of imidazole and N-methylimidazole with concomitant dealkylation. The cleaved-off alkyl groups, apparently in cationic form, react with the anions present, accounting for the formation of alkyl chlorides and alkyl acetates from the chloride ILs and acetate ILs, respectively. A second, minor pathway comprises the degradation of the imidazole ring under conversion of the C2-unit from the former C4-C5 moiety into ethylenediamine and reaction of the C1-unit from the former C2 with the IL anions. Because of the non-neglible byproduct formation, the degradation of the ILs upon beta-irradiation and possible side reactions of the resulting byproducts need to be kept in mind for all setups that involve beta-irradiation and imidazolium ILs simultaneously. Graphical abstract

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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

Lehrhofer,

Bacher,

Hettegger

et al. 2024

Cellulose

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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

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β-Irradiation in the presence of 1,3-dialkylimidazolium ionic liquids causes covalent cellulose derivatization with simultaneous nitrogen incorporation

Cited by 4 publications

References 54 publications

State-of-the-Art Irradiation Technologies for the Waste Biomass Pretreatment: Potential and Challenges

State-of-the-Art Irradiation Technologies for the Waste Biomass Pretreatment: Potential and Challenges

beta-Irradiation of pure 1-alkyl-3-methylimidazolium-based ionic liquids

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

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