Is Carbene Formation Necessary for Dissolving Cellulose in Ionic Liquids?
S Gehrke and K Schmitz and O Holloczki, JOURNAL OF PHYSICAL CHEMISTRY B, 121, 4521-4529 (2017).
In this work we explored through molecular dynamics simulations how the dissolution of cellulose and its fragments in 1-ethyl-3-methylimidazolium acetate is, affected by the inherent accessibility of carbenes in this solvent. We show that apart from the decomposition reactions carbenes do not interact strongly with the solute carbohydrates, as the solute solvent interactions are dominated by the anion. On the other hand, the formation of the carbene is hindered by the hydrogen bond donor hydroxyl groups at the carbohydrate through occupying the anion, and hence disrupting the anion cation interplay. Comparing the rate of dissolution of a cellulose bundle in the pure IL to that in the presence of carbenes showed that not only the cellulose hinders the carbene formation, but the presence of carbenes also make the dissolution of the Cellulose slower. Accordingly, although based on indirect experimental findings one might speculate otherwise, the solubility and carbene formation are merely two independent consequences of the basicity of the ionic liquid anion, and the presence of carbenes is not necessary for breaking up the cellulose into individual chains. Based on these results we can conclude that it is, in principle, possible to design an ionic liquid that is an ideal solvent for this biopolymer, which dissolves, but does not decompose cellulose.
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