Cu(0) onto sulfonic acid functionalized silica/carbon composites as bifunctional heterogeneous catalysts for the synthesis of polysubstituted pyridines and nitriles under benign reaction media

A series of novel and highly efficient bifunctional heterogeneous catalysts based on Cu(0) onto sulfonic acid functionalized silica/carbon composites derived from silica and inexpensive natural organic materials (starch, glucose, maltose, cellulose and chitosan) were successfully synthesized. The utility of the developed catalysts was explored for the one-pot synthesis of polysubstituted pyridines under solvent-free conditions and for the oxidative transformation of aldehydes to nitriles using aqueous ammonia and H2O2. Among the different catalysts screened, Cu(0)-SilC(cell)-SO3H was found to be the most active and selective. The prepared bifunctional composites were characterized by FTIR, TGA and CHNS, while the most active catalyst, Cu(0)-SilC(cell)-SO3H was further characterized by SEM, TEM, XRD, EDX, ICP-AES and XPS analysis. Further, the catalyst can be recovered and reused for atleast six runs without any significant impact on catalytic activity and selectivity. The high catalytic activity, thermal stability, simple recovery, reusability and eco-friendly nature of the catalyst makes the present protocol particularly attractive from the view point of green chemistry.