New chitosan-imine derivatives: from green chemistry to removal of heavy metals from water/ Nuevos derivados imino-quitosano: desde la quimica verde a la remocion de metales pesados en aguas

Three novel imine-chitosan derivatives were synthesized by condensation of the amino terminals of chitosan and 4-bromomethyl-2-hydroxybenzaldehyde [A.sub.1], 4-formyl-2-hydroxybenzoic acid [A.sub.2], and (E)-6-((2-(pyridin-2-yl)hydrazono)methyl)picolinaldehyde [A.sub.3]. Noteworthy, is the aqueous synthesis of imine-chitosan compounds using relatively mild conditions (70[degrees]C) in a green chemistry fashion. The new compounds were characterized by [sup.1]H-NMR, FT-IR, elemental analysis, thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). A solubility study at different pH values was performed for the three compounds, obtaining very different behaviors when compared to that of the pristine chitosan. Finally, by means of atomic absorption the ability to remove heavy metal ions, such as Pb(II) and Hg(II), was investigated for the imine-chitosan derivatives, which showed a high removal percentage at basic pH (between 8-10) but low removal percentage at pH lower than 5. Additionally, the nature of the substituent determines the solubility of the resulting adducts thus widening the potential applications of chitosan derivatives.