Ionic liquid mediated technology for synthesis of cellulose acetates using different co-solvents

• It was possible to dissolve more than 12 wt% cellulose with DP 1000–1100 in [HDBN][OAc]/dispersing agent system in 15 min.
• Acetone, acetonitrile, DBN or DMSO was used as the dispersing agent.
• The cellulose was insoluble in the dispersing agentsexcept DBN, where it dissolved more than 10 wt% cellulose at 70 °C.
• The cellulose acetates produced were soluble in acetone, chloroform, DMSO and dichloromethane.
• The DS of cellulose acetate produced from recycled ionic liquid was comparable with that of fresh ionic liquid.

In this work, cellulose acetate was synthesized under homogeneous conditions. Cellulose was first dispersed in acetone, acetonitrile, 1,5-diazabicyclo(4.3.0)non-5-ene (DBN) or dimethyl sulphoxide (DMSO) and the resulting suspension was dissolved in an ionic liquid, 1,5-diazabicyclo(4.3.0)non-5-enium acetate [HDBN][OAc] at 70 °C for 0.5 h. It was possible to dissolve more than 12 wt% cellulose with a degree of polymerization in the range of 1000–1100. The dissolved cellulose was derivatized with acetic anhydride (Ac2O) to yield acetylated cellulose. As expected, the use of the co-solvents improved the acetylation process significantly. In fact, cellulose acetates with different properties could be obtained in half an hour, thus facilitating rapid processing. When DBN was used as the dispersing agent (the precursor of the ionic liquid), the problems associated with recycling of the ionic liquid were significantly reduced. In fact, additional [HDBN][OAc] was obtained from the interaction of the DBN and the by-product, acetic acid (from Ac2O). However, the cellulose acetate obtained in this manner had the lowest DS. Consequently, the native cellulose and acetylated celluloses were characterized by means of 1H- and 13C-NMR, FT-IR, GPC/SEC and by titration. The cellulose acetates produced were soluble in organic solvents such as acetone, chloroform, dichloromethane and DMSO which is essential for their further processing. It was demonstrated that the ionic liquid can be recovered from the system by distillation and re-used in consecutive acetylation batches.