Acid functionalized ionic liquid catalyzed transformation of non-food biomass into platform chemical and fuel additive

Abstract

This paper reports the synthesis of sulfonic acid functionalized Brønsted acidic ionic liquids (BAILs) using N,N-dimethyl acetamide [DMA]+, N-methylpyrrolidone [NMP]+ and 1-butyl-3-(4-sulfobutyl)imidazole [BBIM-BuSO3H]+ as cation, and methanesulfonyl [CH3SO3]− or (OTh−), trifluoromethanesulfonate [CF3SO3]− or (OTf−), and bis((trifluromethyl)sulfonyl)amide [(CF3SO3)2N]− or (NTf2−) as anion source. The ionic liquids (ILs) demonstrated excellent catalytic performance in the valorization of waste streams of biomass to 5-hydroxymethylfurfural (HMF) and 5-ethoxymethylfurfural (EMF), a high-value platform chemical and a promising biofuel additive. Catalytic screening indicated that BAILs containing NTf2 anion exhibits superior performance, giving highest HMF yield. Strong electron withdrawing properties of the trifluoromethyl functionality of [NTf2]− anion is proposed for this high activity of these BAILs. Detailed studies using NMR reveal the reaction proceeds through the (i) depolymerization of cellulose into glucose, followed by (ii) glucose isomerization to fructose and then the product HMF is formed by (iii) triple dehydration of fructose to HMF. Direct conversion of mushroom to EMF is also observed in one-pot with high yield when ethanol is used as a solvent in access amount. DFT calculations elucidated that the catalytic performance of the ILs followed the order of their deprotonation energies (DPE) which can be correlated directly to the residual charge on the Brønsted acidic proton. This study of valorization of waste mushroom coupled with DFT calculations, revealing DPE as an important descriptor, is likely the first report of this kind.