Azide pre-click modification of chitosan: N-(2-azidoethyl)chitosan

N-(2-Azidoethyl)chitosan was synthesized from low-molecular-weight chitosan (molecular weight 37 000 and degree of deacetylation 0.74) in three steps: (1) reaction of chitosan with chloroacetaldehyde to form a Schiffbase, (2) reduction of the Schiffbase with sodium borohydride, and (3) treatment of the reduction product with sodium azide. The course of the formation of the Schiffbase (this step is determining for the degree of substitution of the final product) was affected by the molar ratio of the reagents, the reaction time, and, primarily, the pH value of the medium. This method for selective to an amino group, does not require harsh conditions, and can be proposed for the azide pre-click modification of chitosan.