Acid-functionalized Ionic Liquid Catalyzed Hydrolysis Of Cellulose And Chitosan Under Microwave Irradiation

The most potential and ideal way to apply cellulose is through hydrolyzation to obtain cellobiose, glucose and 5-hydroxymethylfurfural. Chitosan is an environmental friendly crude macromolecule material. However, high molecular weight and low solubility limit its applications, especially in medicine and food industry. Chitooligosaccharides is the degradation product of chitosan possessing lots of excellent capabilities. It has important value in wide fields, such as medicine, feeding stuff and biology agriculture. Cellulose and chitosan can be hydrolyzed by different methods including chemical, physical and biological hydrolysis. Ionic liquids are mental salts at room temperature which are promising solvent for dissolving polysaccharides such as chitosan and cellulose. The functionalized ionic liquids with Br(?)nsted acidity can be obtained by moderating the cations or anions; such functionalized ionic liquids posess the advantage of solid acid and liquid acid.In this study, 1-butyl-3-methylimidazolium chloride (BmimCl), l-Ally-3-methylimidazolium chloride (AmimCl) and 1-H-3-methylimidazolium chloride (HmimCl), 1-(3-sulfonic acid) propylimidazolium hydrogen sulfate ([PSmim][HSO4]), 1-(3-sulfonic acid) propylimidazolium toluenesulfonate ([PSmim][TSA]), 1-(3-sulfonic acid) propylimidazolium mesylate ([PSmim][CH3SO3]), 1-(3-sulfonic acid) propylpyridinium hydrogen sulfate ([PSPy][HSO4]),1-(3-sulfonic acid) propylpyridinium toluenesulfonate ([PSPy][TSA]),1-(3-sulfonic acid) propylpyridinium dihydrogen phosphate ([PSPy][H2PO4]),1-(3-sulfonic acid) propyltriethylaminium hydrogen sulfate ([PSTEA][HSO4]),1-(3-sulfonic acid) propyltriethylaminium toluenesulfonate ([PSTEA][TSA]), were synthesized and characterized by H-NMR. Ethanenitrile was used as molecular probes to measure the acidities of ionic liquids by FT-IR.Hydrolysis of cellulose in BmimCl was carried out under microwave irradiation (MW) using imidazolium acidic functionalized ionic liquids as catalysts and DMSO as cosolvent. The dinitrosalicylic acid (DNS) method was employed to measure the total reducing sugar (TRS) yield. Hammett method was adopted to determine the acidity of the acidic functionalized ionic liquids. The effect of DMSO loading, water loading and catalyst amount on the TRS yield were investigated. The results showed that the acidity of the acid-fuctionalized ionic liquids was relevant to the catalytic activity. And the optimal reaction conditions were as follows:amount of catalyst 0.05 g; microwave power 640 W and irradiation time 60 s.Hydrolysis of chitosan in ionic liquids was carried out under microwave irradiation (MW) using pyridinium acid functionalized ionic liquids as catalysts, and DMSO as co-solvent. The total reducing sugar was analyzed by Imoto method. The acidity of the pyridinium ionic liquids was determined by Hammett method. The structures of the original and degraded chitosan were characterized by Fourier-transform infrared spectra, Uv-vis spectra, X-ray powder diffraction analysis and 13C NMR spectroscopy. The viscosity-average molecular weight of degraded chitosan was determined by viscometric method. The optimal reaction conditions were estimated by orthogonal test. The influence of microwave power and irradiation time was further studied. The results show that the structures of the original and degraded chitosan undergone no change; the catalytic activity of pyridinium ionic liquids is relevant to their acidity; the optimal reaction conditions are as follow: [PSPy][HSO4] 1.5 g, microwave irradiation 640 W, irradiation time 120 s, the total reducing sugar reached 92%.