Efficient Chitin Derivatization Methods Using Ionic Liquids and Deep Eutectic Solvents

Ionic liquids (ILs) and deep eutectic solvents (DESs) have emerged as effective solvents for poorly soluble materials such as natural polysaccharides, including chitin. This review describes recently developed efficient chitin derivatization methods that harness the solubilizing power of ILs and DESs. It covers chitin acylation approaches, including acylation and mixed ester formation, as well as chitin etherification protocols. For example, the ILs 1-allyl-3-methylimidazolium bromide (AMIMBr) and 1-allyl-2,3-dimethylimidazolium bromide serve as effective media for chitin acylation and etherification, respectively, yielding single esters and benzyl derivatives with high degrees of substitution (DS). The use of DESs comprising AMIM chloride (AMIMCl) as a hydrogen bond acceptor and several hydrogen bond donors for chitin acylation are presented. In an optimized system, acylation using acyl chlorides proceeded smoothly without additives, such as a base/catalyst, in a DES comprising AMIMCl and 1,1,3,3-tetramethylguanidine, affording high-DS ester derivatives. The method was extended to the synthesis of mixed chitin esters bearing both long and bulky acyl substituents at appropriate substitution ratios, which exhibit thermoplasticity.