A convenient solvent system for cellulose dissolution and derivatization: Mechanistic aspects of the acylation of the biopolymer in tetraallylammonium fluoride/dimethyl sulfoxide

This work is concerned with the dissolution of cellulose in tetraallylammonium fluoride/DMSO; the thermal stability of electrolyte solution, and relevant mechanistic aspects of the biopolymer acylation. EMF measurements (fluoride ion-selective electrode) showed that the electrolyte is present as monohydrate. 1H NMR spectroscopy showed that it does not undergo elimination via ylide intermediate, even after heating for 21 h at 70 °C. A solution of TAAF in DMSO readily dissolves microcrystalline and fibrous celluloses (cotton and eucalyptus); the dissolved biopolymer can be derivatized into esters by reaction with carboxylic acid anhydrides. Cellulose ethanoate, butanoate, hexanoate, and mixed esters, ethanoate/butanoate, ethanoate/hexanoate were conveniently synthesized under homogeneous reaction conditions (3 h at 60, 80, and 100 °C). Using longer reaction times (12, 18 h) lead to esters of low degree of substitution, due to fluoride-ion mediated ester-hydrolysis. The intermediate formation of acyl fluorides in this medium has been confirmed by FTIR spectroscopy.