Transamidation of secondary amides with amines by using Al2O3 AS AN efficient heterogeneous catalyst

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, we have shown the successful example of a reusable catalyst for transamidation of secondary amides with amines by Al2O3 catalyst. Al2O3 is an amphoteric catalyst which activates carbonyl carbon of secondary amide group and also helps to C-N cleavage of reactant amide group by attacking N-H hydrogen. By using the concepts of amphoteric properties of Al2O3, amides were synthesized from secondary amides and amines in presence of triethylamine solvent. Several aliphatic and aromatic amines were used for transamidation of N-methylbenzamide in presence of Al2O3 catalyst. Among them n-octylamine, benzylamine, aniline, o-toluedine and m-toluedine were found as efficient reactants to produce desired amide products with good to high isolated yields by transamidation reactions. Theoretical calculations have also been done to find out the mechanistic pathway of this transamidation reaction. Theoretical calculation shows that LUMO of carbonyl carbon of secondary amide interacts with HOMO of nitrogen of amine in presence of Al2O3. So, the reaction was successful for transamidation of secondary amide with amines even if in presence of basic solvent trietylamine. The Intrinsic Reaction Coordinate (IRC) has also been calculated to find out the transition state of the reaction. Finally, after completion of reaction, catalyst was separated from the mixture by centrifugation and dried in oven at 90 °C for 24hrs and it was reused for four times without any significant loss of it’s 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 novel and sustainable method for transamidation of secondary amides with amines using Al2O3 as a reusable, inexpensive, and commercially available heterogeneous catalyst with tolerance to the co presence of basic molecules.

Key words: Amide, amine, transamidation, Al2O3, heterogeneous catalyst.