Ionic Liquids as Reaction Medium in Cellulose Functionalization

Summary: The application of different ionic liquids (IL), namely 1‐N‐butyl‐3‐methylimidazolium chloride ([C₄mim]⁺Cl⁻), 3‐methyl‐N‐butyl‐pyridinium chloride and benzyldimethyl(tetradecyl)ammonium chloride were investigated as solvents for cellulose. The ILs used have the ability to dissolve cellulose with a degree of polymerization in the range from 290 to 1 200 to a very high concentration. Using [C₄mim]⁺Cl⁻, no degradation of the polymer appears. By ¹³C NMR measurement it was confirmed that this IL is a so‐called non‐derivatizing solvent. [C₄mim]⁺Cl⁻ can be applied as a reaction medium for the synthesis of carboxymethyl cellulose and cellulose acetate. Without using any catalyst, cellulose derivatives with high degree of substitution could be prepared.

¹³C NMR spectrum of cellulose dissolved in the IL [C₄mim]⁺Cl⁻ (top). The ¹³C NMR spectrum of cellulose dissolved in DMSO/tetrabutylammonium fluoride trihydrate is shown for comparison (bottom).