Facile and efficient synthesis of N-benzyl chitosan via a one-pot reductive amination utilizing 2-picoline borane

In this paper, the use of 2-picoline borane (pic-BH3) as a reducing agent for the reductive amination of chitosan is reported for the first time. By optimizing the feed molar ratio of chitosan, benzaldehyde and pic-BH3, a high yield of isolated N-benzyl chitosan with a nearly perfect degree of substitution is successfully obtained. This material has rarely been obtained with previous methods. The newly developed synthetic method herein has many advantages, including being more facile, more efficient, and less harmful than conventional methods; thus, this method is applicable to other aldehydes or ketones, leading to wide varieties of N-modified chitosan in the future. For the first time, this paper revealed that 2-picoline borane (pic-BH3) functioned well in the reductive amination of chitosan. Therefore, N-benzyl chitosan with a nearly perfect degree of substitution was successfully obtained, which has rarely been achieved by other synthetic methods. The new method herein has many advantages, including being more facile, more efficient, and less harmful than conventional methods; thus, this method is applicable to other aldehydes or ketones, leading to a wide variety of N-modified chitosan specimens with desirable degrees of substitution in the future.