Degradation of cellulosic materials by heating in DMAc/LiCl

N,N-Dimethylacetamide (DMAc, 1)/lithium chloride is a frequently used solvent system for cellulosic materials. Heating or refluxing insoluble samples in DMAc/LiCl represents a common protocol for facilitating the subsequent dissolution. It is shown by kinetics using gel permeation chromatography (GPC) that the improved solubility is not caused by an alleged ‘activation’ of the pulp, but by progressing degradation of the cellulosic material. Ketene aminal 2 and N,N-dimethylketeniminium ions (3), the latter being known as reagent for cleavage of ethers and acetals, have been demonstrated to be present in DMAc and DMAc/LiCl at elevated temperatures by specific trapping of these intermediates in a Claisen rearrangement and in a thermal [2+2]-cycloaddition, respectively.