Synthesis of functional surfactants derived from chitosan and their characteristics

Abstract

[Preparation of Chitosan Oligomers by Concentrated Hydrochloric Acid] Chitosan was partially hydrolyzed with 35 % hydrochloric acid for 2 hours at 80℃ and the hydrolyzate stored at - 20℃ after dilution with water to precipitate higher molecular weight (MW) chitosan oligomers. When the hydrolyzate was not diluted with water, no precipitate was formed but 7.3 % chitosan oligomers were precipitated at a dilution ratio of 1.0 (ml water/ml hydrolyzate). The time for precipitation was not significantly changed after storing the hydrolyzate at - 20℃ for 1 day. In addition, the precipitation yield was not significantly influenced by the concentration of HCl used for the hydrolysis except at less than 5.0 (ml HCl/g chitosan). However, the yield of precipitated oligomers changed with partial hydrolysis time. For 0.5 and 2 hour hydrolysis, 10.1 and 7.3 % of the oligomers were precipitated, respectively, but only 3.1 % of the oligomers were obtained after a 4 hour reaction. When methanol was added to the hydroly zate, the precipitation yield increased up to 70 % but the amounts of lower MW chitosan oligomers in the precipitated oligomers also increased with the increase of higher MW. The precipitated oligomers were mainly composed of pentamers and hexamers. [Oxidative Synthesis of Chitosan-Based Surfactants] A chitosan-based surfactant (CBS) having n-alkyl chain length of 12 carbon atoms [CBS-C12; {O-β-2-amino-2-deoxy-D-glucopyranosyl-($1 \to 4$)}$_{n-1}$-2-amino-2-deoxy-N-n-dodecyl-D-gluconamide] was synthesized by introduction of dodecyl amine to δ-lactone group at the final unit of chitosan oligomer. Chitosan oligomers were produced by acid hydrolysis with concentrated hydrochloric acid, oxidized with potassium iodide, and de-ionized with Dowex 50W-X4 to give the chitosan oligo-lactone [{O-β-2-amino-2-deoxy-D-glucopyranosyl-($1 \to 4$)}$_{n-1}$-2-amino-2-deoxy-D-glucono-1,5-lactone]. When chitosan oligomer I, II, and III were oxidized in $I_2$/KOH solution for 24 hours ...