A Heterogeneous Niobium(V) Oxide Catalyst for the Direct Amidation of Esters. Issue 17 (11th August 2015)

• Record Type: Journal Article
• Authors: Ali, Md. Ayub; Siddiki, S. M. A. Hakim; Kon, Kenichi; Shimizu, Ken‐ichi
• Is Part Of: ChemCatChem. Volume 7:Issue 17(2015:Sep.)
• Page Start: 2705
• Page End: 2710
• Publication Date: 2015-08-11
• Subjects: Catalysis -- Periodicals; 541.39505
• DOI: 10.1002/cctc.201500601
• Languages: English
• ISSNs: 1867-3880

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>This study reports the first example of a heterogeneous catalytic system for the direct amidation of various esters with amines. Of 25 types of catalyst, Nb₂O₅ shows the highest activity in the amidation of methyl benzoate with aniline. Nb₂O₅ gives high yields in the amidation of various esters and amines under solvent‐free conditions, is reusable, and shows higher turnover numbers than previously reported homogeneous catalysts such as La(OTf)₃. IR spectroscopic studies of ethyl acetate adsorbed on the catalysts show a strong acid–base interaction between the Nb⁵⁺ Lewis acid site and carbonyl oxygen, which can result in high reactivity of the ester with a nucleophile (amine) and, thus, high activity of Nb₂O₅. Kinetic results show that the activity of Nb₂O₅ does not markedly decrease with increasing aniline concentration, in contrast to reference catalysts TiO₂ and La(OTf)₃. The relatively low negative impact of basic molecules on the Lewis acid catalysis of Nb₂O₅ also enables its high activity.</p> </abstract>