Hydrolytic Processes and Condensation Reactions in the Cellulose Solvent System N,N-Dimethylacetamide/Lithium Chloride. Part 1.

Abstract

Summary Refluxing of cellulose samples in N,N-dimethylacetamide (DMAc, 1), or in DMAc containing low concentrations of LiCl, is a common protocol to facilitate dissolution of the cellulose for GPC measurements. The formation of chromophoric condensation products, whose structures have been elucidated for the first time, and of secondary chromophores by reaction with carbohydrate structures has been demonstrated. DMAc containing traces of water is slowly hydrolyzed to dimethylammonium acetate (2) under reflux conditions. The reaction is accelerated in the presence of lithium chloride. In contrast, absolute DMAc produces five different condensation products upon thermal treatment, which were isolated by non-traditional column chromatography approach. The primary condensation product N,N-dimethylacetoacetamide (3) is formed as the major component and acts as the precursor to the other chromophore products, namely dehydroacetic acid and isodehydroacetic acid derivatives. Compound 3 is able to form furan derivatives by reaction with reducing end groups or carbonyls in carbohydrate structures as demonstrated by reactions with model compounds. As a consequence, it must be concluded that heating/refluxing in DMAc or DMAc/LiCl generates a number of potent chromophores from the solvent and, furthermore, can chemically alter pulp samples by introducing reactive structures.