Dissolution of cellulose in 1-allyl-3-methylimizodalium carboxylates at room temperature: A structure-property relationship study

The development of highly efficient cellulose solvents is imperative to the effective utilization of cellulose. In this work, ionic liquids (ILs) with the same 1-allyl-3-methylimidazolium cation ([Amim]+) but different carboxylate anions, such as formate ([HCOO]−), acetate ([CH3COO]−), propionate ([CH3CH2COO]−), butyrate ([CH3CH2CH2COO]−), glycollate ([HOCH2COO]−), lactate ([CH3CHOHCOO]−) and benzoate ([C6H5COO]−) were synthesized, and their thermal properties and viscosities were determined. Then these ILs were used to investigate the effect of anion structure on solubility of cellulose in the ILs. It was shown that the viscosity and cellulose solubility depended strongly on the anion structure of the ILs. For example, at 30 °C solubility of cellulose in [Amim][CH3CH2COO] was as high as 19.0%, whereas cellulose was not soluble in [Amim][HOCH2COO], [Amim][CH3CHOHCOO] and [Amim][C6H5COO]. In addition, solvatochromic UV/vis probe and 13C NMR measurements were performed to demonstrate dissolution mechanism of cellulose in the ILs. The results suggested that although cations of the ILs have un-negligible contribution to the highly efficient dissolution of cellulose, hydrogen bonding interactions of anions of the ILs with cellulose is predominant.