Abstract:
Diamides are one of the most important compounds in chemical and pharmaceutical industries. Conventionally, diamides are prepared from dicarboxylic acids and amines or diamines via activated dicarboxylic acids and their derivatives such as dicarboxylic acid anhydrides or acylchlorides or through activation with a stoichiometric amount of a condensation agent. These methods have some limitations of low atom efficiency, separation of products from the reaction mixture and production of byproducts. Lewis acid catalyst was reported for amide bond formation from carboxylic acids with amines has additional drawbacks, such as limited substrate scope and high catalyst loading. These drawbacks may be caused by the suppression of Lewis acid sites of the catalyst by basic molecules (amines and water as byproduct), present in the reaction mixture. Recently, it was reported that Nb2O5 was used as water and base tolerant heterogeneous Lewis acid catalyst for amide bond formation.
By using the concepts of water and base tolerant properties of Nb2O5, diamides were synthesized from dicarboxylic acids and amines in presence of Nb2O5. Several Lewis and Brønsted acid catalysts were tested for the synthesis of N, N-dioctyl-butanediamide from succinic acid (1 mmol) and n-octylamine (2 mmol) at different conditions. Among these catalysts Nb2O5 showed highest catalytic activity to the corresponding N, N-dioctyl-butanediamide at 135 °C. After the completion of reaction catalyst was separated from the mixture by centrifugation. Other diamides were also synthesized using Nb2O5. The catalyst, Nb2O5 was reused for four cycles without a marked decrease in the yield of the product. The products were purified by recrystallization separation technique. The synthesized pure diamide products were identified by UV-VIS Spectrophotometer, FT-IR, 1H-NMR and 13C-NMR. Catalyst was characterized by several chemical reactions and XRD.
In conclusion, a novel, versatile and sustainable method was developed for the synthesis of diamides from dicarboxylic acids and amines using Nb2O5 as a base tolerant heterogeneous catalyst.
