N,O-carboxymethyl chitosan and preparative method therefor

Claim 1

N,O-carboxymethyl chitosan having a degree of substitution of carboxymethyl groups per glucosamine monomer unit in the chitosan of less than 1.0, with carboxymethyl groups being substituted on hydroxyl oxygen atoms of the glucosamine monomer units of the chitosan and carboxymethyl groups being substituted on nitrogen atoms of the glucosamine monomer units of the chitosan.

Claim 3

A method for the preparation of N,O-carboxymethyl chitosan which comprises (a) dispersing solid chitosan in a liquid medium of the group consisting of isopropyl alcohol, n-butanol, isobutanol, methyl ethyl ketone, toluene, and ethanol-toluene mixtures containing at least 72 mol percent toluene, to form a slurry, (b) steeping the chitosan in caustic medium by adding strong aqueous sodium hydroxide solution to the slurry, in a proportion of three to eight mols sodium hydroxide per mol of glucosamine monomer unit in the chitosan, with stirring to maintain the chitosan dispersed in the caustic medium for a period of from 0.5 to 1.0 hours, (c) thereafter adding monochloroacetic acid to the caustic medium, in a proportion of substantially one mol of the acid for each 1.8 to 2.2 mols of sodium hydroxide in the caustic medium, and heating the slurry with continued stirring to a reaction temperature of from substantially 40° C. to substantially 70° C., (d) maintaining the stirred slurry at the reaction temperature for a reaction period of substantially two to twelve hours and sufficient to complete reaction between the chitosan and sodium monochloroacetate to form N,O-carboxymethyl chitosan, (e) adding to the slurry a small portion of water and a portion of glacial acetic acid in amounts sufficient respectively to enable measurement of the pH of the suspending liquid, and to bring the pH of the slurry to substantially 7.0, and (f) recovering the N,O-carboxymethyl chitosan product from the slurry by separating the solid thereof and washing same with solvents to remove extraneous salts without dissolving the product.

Claim 4

A method for the preparation of N,O-carboxymethyl chitosan which comprises (a) dispersing solid chitosan in a liquid medium of the group consisting of isopropyl alcohol, n-butanol, isobutanol, methyl ethyl ketone, toluene, and ethanol-toluene mixtures containing at least 72 mol percent toluene, to form a slurry, (b) steeping the chitosan in caustic medium by adding strong aqueous sodium hydroxide solution to the slurry, in a proportion of three to eight mols sodium hydroxide per mol of glucosamine monomer unit in the chitosan, with stirring to maintain the chitosan dispersed in the caustic medium for a period of from 0.5 to 1.0 hours, (c) thereafter adding monochloroacetic acid to the caustic medium, in a proportion of substantially one mol of the acid for each 1.8 to 2.2 mols of sodium hydroxide in the caustic medium, and heating the slurry with continued stirring to a reaction temperature of from substantially 40° C. to substantially 70° C., (d) maintaining the stirred slurry at the reaction temperature for a reaction period of substantially two to twelve hours and sufficient to complete reaction between the chitosan and sodium monochloroacetate to form N,O-carboxymethyl chitosan, (e) adding to the slurry a small portion of water and a portion of glacial acetic acid in amounts sufficient respectively to enable measurement of the pH of the suspending liquid, and to bring the pH of the slurry to substantially 7.0, and (f) recovering the N,O-carboxymethyl chitosan product from the slurry by separating the solid thereof and washing same with solvents to remove extraneous salts without dissolving the product.