(1) Chitosan was dissolved in dilute acetic acid and precipitated with excessive acetone to obtain chitosan acetate. Chitosan acetate was transferred into a reaction bottle with stirring. A certain amount of NaOH solution and isopropanol were added, while stirring, the isopropanol solution of chloroacetic acid was added. The reaction temperature was controlled to 70 C, the reaction time was several hours, the reaction temperature was cooled to room temperature, and the pH value was adjusted by dilute acid. Carboxymethyl chitosan was obtained by washing and drying with 85% methanol. [1]

(2) The purified chitosan was packed in a stirred reaction bottle, 20% NaOH solution and isopropanol were added, stirred for 60 minutes at room temperature, and then dripped with isopropanol solution of chloroacetic acid. Golden chitosan was expressed as reacting at room temperature for 5 hours, then neutralized with dilute hydrochloric acid to pH 7 and precipitated with acetone. Filtration, washing with 85% methanol solution until chloride-free ions, then washing with anhydrous methanol, vacuum drying at 60 ~C, the product is obtained. [1]

(3) Add 2 abalone chitosan to 200 mL n-butanol, stir at room temperature for 20 minutes, add lOmol/L NaOH solution for 6 times, 50 mL each time, 40 min each time, stir 40 rnin again after the last addition, get alkaline chitosan, then add 24 g solid chloroacetic acid 5 times, 5 minutes once, stir reaction 3 hours at 55-75 degrees C, and then add 17 mL water. The product was obtained by adjusting the pH value to 7 with glacial acetic acid, filtering, washing with 70% methanol 300 mL, drying with 300 mL absolute ethanol, and drying in vacuum at 60 C. The reaction temperatures of carboxymethylation were 55, 60, 65, 70 and 75 C, respectively. The yield of carboxymethylation was 31.0 g, 33.8 g, 36.58, 34.0 g and 33.2 g, respectively. The highest yield was obtained at 65 C. [1]

(4) Chitin was immersed in 40%-60% NaOH solution at a certain temperature for 0.5-5 h, then added chloroacetic acid while stirring, reacted at 0-70 ~C for 0.5-5 h, the alkali-acid mass ratio was controlled at (1.2-1.6): 1, kept at 0-80 ~C for 5-36 h, then neutralized with dilute hydrochloric acid, separated products, washed with 75% ethanol solution, and dried at 60 ~C. Carboxymethyl chitosan can also be prepared by this method. [1]

(5) 15 g chitosan was first alkalized in 50% (w/w) NaOH solution, then stirred with 150 mL isopropanol, added with 18 g chloroacetic acid, reacted at 65 ~C for 2 hours, neutralized with acid and washed with 70% methanol for many times, then dissolved in water, precipitated with acetone, filtered, washed repeatedly with anhydrous ethanol, filtered and vacuum dried to obtain refined carboxymethyl chitosan. Sugar. [1]