Synthesis of N,O-(Сarboxymethyl)chitosan under Synthesis in Gel Conditions and Its Sorption Properties

Methods for the synthesis of N,O-(carboxymethyl)chitosan with degrees of substitution ranging from 0.1 to 1.7 were developed using alkali metal and ammonium monochloroacetates in a nucleophilic substitution reaction under polymer-analogous synthesis in gel conditions in neutral and alkaline media. The use of sodium monochloroacetate as a functionalizing agent and a weak Brønsted base facilitated the production of a water-soluble polymer with a maximum degree of substitution of 1.1. The addition of NaOH as a stronger base increased the degree of carboxymethylation of chitosan to 1.7. The influence of the chemical structure of sorbents based on N,O-(carboxymethyl)chitosan crosslinked with epichlorohydrin on their sorption capacity towards transition metal ions Cu2+, Ni2+, Co2+, and Zn2+ was revealed. The dependence of the static exchange capacity of the sorbent on the degree of substitution exhibits an extreme character. The maximum capacity was 1.827 mmol/g at a degree of substitution of 0.7, after which the exchange capacity decreases. However, crosslinked polymers with lower static exchange capacity exhibited selective complexation with Cu2+ ions.