Bifunctional Deep Eutectic Solvent For Fructose Dehydration To 5-hydroxymethylfurfural

Biomass,an abundant and readily available feedstock,is attracting considerable interest as a substitute to conventional fossil fuel,because of its sustainability and biodegradability.Particularly,high research attention has been given to the conversion of lignocellulosic biomass-derived carbohydrates into platform chemicals,one of which is 5-hydroxymethylfurfural(5-HMF).5-HMF can be derived to a wide range of biofuel and other high value-added chemicals.Deep Eutectic Solvent(DES),as a green solvent,has been widely applied in the field of biomass pretreatment and conversion.In this work,DES prepared by imidazole(Im)and benzenesulfonic acid(BSA)is used as both acidic catalyst and reaction solvent in fructose dehydration to 5-HMF.The formation mechanism and thermal stability of DES,as well as the bifunctionality of DES in fructose dehydration is intensively studied.Moreover,reaction conditions are systematically optimized for improving reaction performance,and the reaction mechanism of fructose dehydration in DES is explored.In order to investigate the formation mechanism,DES is characterized by FT-IR and 1H NMR,whose results indicates that the DES formation process involves an acid-base neutralization reaction between BSA and Im,and subsequently strong interaction through the equimolar salt[Im:BSA]and excessive BSA.The results of COSMO-RS calculation further verify the existence of hydrogen bond between[Im:BSA]and BSA.Moreover,DES exhibits high thermal stability,whose decomposition starts from 238℃.As for fructose dehydration into 5-HMF,DES shows high catalytic performance in a very short reaction time.Based on COSMO-RS model,the solvent effect of DES is verified through the hydrogen bond between fructose and DES.In the optimal experimental conditions,the BSA-rich DES[Im:1.5BSA]with 1:1.5 of Im to BSA(mole ratio)and 10%dosage exhibits a high 5-HMF yield of 90.1%at 100℃ in 3 minutes.In addition,the reaction mechanism for fructose dehydration clarifies the roles of hydrogen proton as electrophiles and BSA anion as nucleophile,and three H2O molecules are eliminated from fructose.