Carboxymethyl chitosan is a kind of chemical synthesis in recent years, which has important significance in medicine, chemical industry, environmental protection and health care products. Its stable nature and pharmacological effects such as antibacterial, anti infection, lipid-lowering and prevention of arteriosclerosis determine that it will play a greater role in human daily life in the future. Carboxymethyl chitosan is a kind of water-soluble chitosan derivative, which has many characteristics, such as strong antibacterial, fresh-keeping, amphoteric polyelectrolyte and so on. It has many applications in cosmetics, fresh-keeping, medicine and so on. It is also one of the chitosan derivatives which have been studied more in recent years.

Carboxymethyl chitosan can also be obtained by the reaction of chloroacetic acid with carboxymethyl chitin in the presence of alkali, just like the preparation of carboxymethyl chitin, but the carboxymethyl of carboxymethyl chitin is substituted on the C6-OH of sugar residue, and a small amount of carboxymethyl is substituted on the c3-oh to produce O-carboxymethyl chitin. The situation of chitosan is more complicated. Carboxymethyl can be substituted not only on - Oh, but also on - NH to form O-carboxymethyl and N-carboxymethyl chitosan. In fact, there are several possible substitutions: c6-o-carboxymethyl and c2-n_ Carboxymethyl, c3-o-carboxymethyl, c6-o, c2-n-carboxymethyl, c6-o, c3-o, c2-n-carboxymethyl, etc. Gold chitosan carboxymethyl chitosan indicates that carboxymethylation at C3 is difficult to occur due to steric hindrance effect at C3 and intramolecular hydrogen bond between C2 and C3, so carboxymethyl substitution at hydroxyl group is less, c3-o-carboxymethyl group is less, and c6-o-carboxymethyl group is the main one. For C6-OH and C2 -- NH, the substitution activity of carboxymethyl on hydroxyl group is higher than that of amino group under alkaline condition. Therefore, when the degree of substitution is less than 1, the substitution of carboxymethyl is mainly on hydroxyl group rather than amino group. Only when the degree of substitution is close to 1 and higher than 1, carboxymethyl substitution occurs on amino group to form o, N-carboxymethyl chitosan. The water solubility of carboxymethyl chitosan is not only because it is a kind of sodium carboxylate and soluble in water, but also because the introduction of carboxymethyl destroys the secondary structure of chitosan molecules and makes its crystallinity greatly reduced and almost amorphous.