Green synthesis of a palladium nanocatalyst anchored on magnetic lignin-chitosan beads for synthesis of biaryls and aryl halide cyanation.

Aryl nitriles, Ar-C ≡ N, and biaryls are important precursors of many compounds commonly used in the industry. Production of aryl nitriles and biaryls through a facile method is therefore of significance. In the study the synthesis of aryl nitriles and biaryls with various substituted groups was successfully achieved using a simple but efficient palladium nanocatalyst system. The nano-catalyst system, (Pd NPs@Fe3O4/lignin/chitosan), was easily prepared by decorating palladium nanoparticles on the magnetic lignin/chitosan microbeads without using any toxic reducing agents. Characterization of the catalyst revealed that the size of palladium nanoparticles was lower than 20 nm and the palladium nanoparticles were homogeneously dispersed on the catalyst support; Fe3O4/lignin/chitosan. The catalytic activity of Pd NPs@Fe3O4/lignin/chitosan was tested in the synthesis of a number of various aryl nitriles and biaryls. Pd NPs@Fe3O4/lignin/chitosan catalyzed the conversion of different aryl halides into aryl nitriles in the presence of K4[Fe(CN)6] by producing conversion yields as high as 97%. The system also exhibited good reactions yields up to 98% for synthesis of biaryls. More importantly, due to its magnetic nature, the used catalyst was easily recovered from the reaction media with a magnet, and regenerated and reused for seven runs.