Abstract:
Amides are the most extensively used substances in both synthetic organic and bioorganic chemistry. Unfortunately, the traditional synthesis of amides suffers from some important drawbacks including low atom efficiency, high catalyst loading and separation of products from the reaction mixture and production of byproducts. In this study, it has been shown that the successful example of a reusable Ni/C catalyst preparation for the effective amidation of aldehyde with amines. For catalyst preparation, the commercially available activated carbon was pre- heated by calcination method at 350 ℃ for 3h in a furnace then1g of pretreated activated carbon were impregnated using an aqueous solution of NiCl2.6H2O. The concentration of the solution was such that the final catalyst would have Ni content of 10 wt. %. The carbon supports were dipped into the solution in a proportion of 1g of carbon to 5 mL of 2 mmol NiCl2.6H2O solution. After 15 min of rotation in a hot plate, the mixture was heated and evaporated for 1h. The samples were dried after the impregnating stage by using conventional or microwave heating at 110℃ for 1h. The reduction of the supported precursor by hydrazine reduction which is a new wet- chemical method. First the supported precursor mixed with water in a two necked round bottom flux then 24 mmol of N2H4.H2O (80%) was poured into the above solution instantaneously. The Precipitate on the wall was washed with distilled water. when the solution temperature became 50℃ by cooling in an ambient atmosphere 24 mmol of a 50% NaOH solution was poured instantaneously into the stock solution. The reaction was complete 1h after the temperature reached the second maximum 54℃.The black precipitate was washed six times with distilled water and dried in oven at 60℃ for 24h.Then it was characterized by several modern techniques such as scanning electron microscopy (SEM), X - ray diffraction (XRD) etc. Then the catalytic activity of Ni/C will be checked and evaluated by a model reaction. For the model reaction, two reactants (benzaldehyde and benzyl amine) will be mixed in a round bottom flask different ratios to the catalyst. Then the solvent will be added to the reaction mixtures. Then the reaction mixture will be heated in the presence of o-xylene reflux condition for 36 h. The progress of the reaction will be monitored by thin layer chromatography with appropriate solvent ratio. Finally, completion of the reaction will be confirmed by TLC. after completion of reaction, catalyst was separated from the mixture by centrifugation and dried in oven at 90 °C for 3h. and it was reused for three times without any significant loss of its catalytic activity. The products were purified by recrystallization and column chromatography techniques. The synthesized pure amide products were identified by FT-IR, 1H-NMR and 13C-NMR.
In conclusion, we have demonstrated a sustainable method for amidation of Aldehyde with amines using Ni/C as a reusable, inexpensive, and commercially available heterogeneous catalyst.
