(190k) Theoretical Investigation of the Mechanism for [Emim]Ac Dissolve Cellulose

Despite ILs are capable of dissolving cellulose, the mechanism of this dissolution process is not well understood. To date, about the mechanism of ILs dissolving cellulose, speculation, ¹³C NMR analysis  and molecular dynamics simulations  have been used to interpret it by some researchers. However, it has not been qualitatively studied by the methods of quantum chemical (QM) calculations and atom in molecules (AIM) theory. In this work, QM calculations and AIM theory have been used to investigate the mechanism of ionic liquid 1-ethyl-3-methylimidazolium acetate ([emim]Ac) dissolving cellulose. It was found that the absolute value of interaction energies of [emim]Ac with cellulose monomer is bigger than that of cellulose dimer. [emim]Ac interacts with cellulose or water molecules mainly via H-bonds. Moreover, the anionic part of [emim]Ac plays a major role in the interaction with them. Further research suggests that the H-bonds between cellulose and [emim]Ac are weaken or even destroyed when the water are added to the [emim]Ac-cellulose system which indicates that water molecules prefer to form H-bonds with [emim]Ac. Consequently the H-bonds between cellulose monomers connected again, and cellulose would precipitate out from the [emim]Ac-cellulose liquor.