Facile enhancement of the deacetylation degree of chitosan by hydrothermal treatment in an imidazolium-based ionic liquid

Abstract

We propose a facile and efficient deacetylation method of chitosan using 1-butyl-3-methylimidazolium acetate (BMIMOAc) as the reaction medium and catalyst. In the proposed method, chitosan is first dissolved in BMIMOAc at 100 °C under vacuum. After the chitosan is completely dissolved in BMIMOAc, water is added to the chitosan–BMIMOAc solution. The chitosan–BMIMOAc–water mixture is heated to 100 °C under a nitrogen atmosphere. Afterwards, the water in the mixture is removed by vacuum heating at 100 °C. The hydrothermally treated chitosan in BMIMOAc is recovered by dialysis followed by repeated washing with methanol and acetone. Deacetylation degree (DD), estimated by colloid titration, of commercial chitosan was enhanced from 77% to 86% by the proposed method. The extent of DD enhancement is larger than in the conventional deacetylation method performed in 9.26 M aqueous sodium acetate, which enhanced the DD to 79%.