Synthesis of Thermoplastic Mixed Chitin Esters

An overview on acylation methods of α-chitin

This article overviews the acylation methods of α-chitin developed over the last four decades. The acylation of polysaccharides has been identified as a useful approach for conferring properties such as thermoplasticity. Owing to the poor solubility of α-chitin, its acylation using acid anhydrides and acyl chlorides has been traditionally investigated under heterogeneous conditions in strong acidic media. Although chitin chains depolymerize under acidic conditions, the resultant derivatives exhibit certain properties and functions. Solvents, such as LiCl/N,N-dimethyladcetamide, ionic liquids, and deep eutectic solvents, are suitable for α-chitin dissolution; therefore, acylation methods for α-chitin under homogeneous conditions have been developed using these solvents as reaction media. The functional materialization of the resultant derivatives was achieved by introducing appropriate substituents and controlling their ratios.

Synthesis of Mixed Chitin Esters via Acylation of Chitin in Deep Eutectic Solvents

The development of efficient derivatization methods of chitin, such as acylation, has been identified to confer new properties and functions to chitin. In this study, we investigate the synthesis of mixed chitin esters via the acylation of chitin in deep eutectic solvents (DESs) comprising 1-allyl-3-methylimidazolum chloride and 1,1,3,3-tetramethylguanidine based on a previous study that reported the development of efficient acylation of chitin in the DES to obtain single chitin esters. A stearoyl group was selected as the first substituent, which was combined with several bulky acyl and long oleoyl groups as the second substituents. After dissolution of chitin in the DES (2 wt%), the acylation reactions were conducted using stearoyl and the desired acyl chlorides for 1 h + 24 h at 100 °C in the resulting solutions. The IR and 1H NMR spectra of the isolated products confirmed the structures of mixed chitin esters with two different substituents. The substituent ratios in the derivatives, which were estimated via the 1H NMR analysis, were changed according to the feed ratios of two acyl chlorides.