Cellulose-supported Poly(hydroxamic acid)-Copper(0) Nanoparticles Catalyst for Aza-Michael Reaction

A green, regenerative and highly active Cu(0) catalyst derived from waste fibre-based cellulose-supported poly(hydroxamic acid) was synthesized. The surface of the hydrolyzed cellulose was undergone chemical modification through graft co-polymerization using methyl acrylate. Then the poly(methyl acrylate) was further converted into poly(hydroxamic acid) bidentate chelating ligand via Wilhelm Lossen rearrangement in an alkaline hydroxylamine aqueous solution. Finally, the copper was impregnated onto the poly(hydroxamic acid) via the adsorption process forming stable five-member ring complex; Cu(II)NPs@PHA. The Cu(II)NPs@PHA is reduces into Cu(0)NPs@PHA using hydrazine hydride as a reducing agent. The Cu(0)NPs@PHA was fully characterized by FT-IR, FE-SEM & EDX, TEM, ICP-OES, TGA, XRD and XPS analyses. The cellulose-supported Cu(0)NPs@PHA was successfully applied to the Aza-Michael addition reaction with several Michael acceptors and various substituted aryl/heterocyclic/alky amine to afford the corresponding C-N product with excellent yield [aryl amine (50-95%); heterocyclic amine (50-96%); alkyl amine (80-98%)]. The Cu(0)NPs@PHA showed extraordinary stability and it was easy to recover from the reaction mixture and could be reused up to five times without loss of its original catalytic activity.