Silica-supported antimony(III) chloride as a mild and reusable catalyst for the Paal–Knorr pyrrole synthesis

Abstract

Heterogeneous catalysts are used for control of environmental pollution. Heterogeneous catalysts are easily separated from the reaction mixture, thus allowing their recovery and re-use. There is a need for catalysts that are efficient under mild conditions. Here, we show that silicasupported antimony(III) chloride (SbCl 3 /SiO 2 ) acts as a highly efficient heterogeneous Lewis acid catalyst for the Paal-Knorr pyrrole synthesis at room temperature. We found that condensation of hexane-2,5-dione with aromatic and aliphatic primary amines in hexane using SbCl 3 /SiO 2 with 7.6 wt% SbCl 3 was the best reaction condition. The silica support facilitated the workup of the reaction mixture and provided a reusable catalyst at least for 7 runs without significant loss in activity. Indeed, the yield was 98% for the first run and 84% for the 7th run. We conclude that low catalyst loading, operational simplicity, practicability and applicability to various substrates make this reaction an interesting alternative to previously applied procedures. From the environmental standpoint, this eco-friendly catalyst is stable, highly active, easy to prepare and handle.

Catalytic activity of the nanoporous MCM-41 surface for the Paal–Knorr pyrrole cyclocondensation

“…All of the products were characterized by a comparison of their spectroscopic data with those of authentic samples [38][39][40]44].…”

“…Taking into account the importance of MCM-41 mesoporous molecular sieves as potential solid catalysts for the synthesis of N-containing heterocycles and our interest in the development of greener protocols for N-heterocyclic condensation [38][39][40], we decided to explore the viability of using MCM-41 to promote the Paal-Knorr pyrrole synthesis (Scheme 1) that, to the best of our knowledge, has not been reported yet.…”

Organonitrogen Chemicals from Oxygen-Containing Feedstock over Heterogeneous Catalysts

“…Heterogeneous catalysts containing Bronsted acid sites or Lewis acids sites are good candidates, and typical examples included layered zirconium sulfophenyl phosphonate, sulfated zirconia, zeolites, montmorillonite clay, − graphene oxide, tungstate sulfuric acid (TSA), molybdate sulfuric acid (MSA), and so on. Another type of heterogeneous catalysts was Bronsted acid or Lewis acids immobilized on solid supports, such as supported sulfuric acid, − Preyssler heteropolyacids, diethylene­triaminepenta­acetic acid, polyethylene glycol 400 coated with sulfonic acid groups, sulfamic acid, antimony­(III) chloride (SbCl 3 ), and gallium trichloride supported (GaCl 3 ) . Compared to homogeneous acids, those solid/supported acids were easily reused, and in addition, their stability, hygroscopic properties, and ease of handling were significantly enhanced, which were important in industry usage …”

Ionic liquid supported on magnetic nanoparticles (-Fe2O3@SiO2-IL-ZnxCly) as the green catalyst for the Paal-Knorr reaction

“…Pyrrole và dẫn xuất của pyrrole là hợp chất hữu cơ quan trọng, với nhiều hoạt tính sinh học như kháng khuẩn, kháng virus, kháng tế bào ung thư [4][5][6]. Ngoài ra, pyrrole còn được tìm thấy trong nhiều loài thực vật với sản phẩm hợp chất tự nhiên như porphyrin, alkaloid, vitamin [7],… Tổng hợp các dẫn xuất của pyrrole thông qua phản ứng Paal-Knorr từ amine bậc một và acetonylacetone đã được nhiều nhà khoa học trong và ngoài nước nghiên cứu và được thực hiện trong hiện diện của các loại xúc tác khác nhau như: acid Brönsted [8][9][10][11] (HCl, H2SO4, p-TSA,…), acid Lewis [8,9,12] (Sc(OTf)3, Bi(NO3)3.5H2O, RuCl3, …), I2 [13], acid proton [14], Al2O3 [15], chất lỏng ion, [16] Bi(OTf)3/[bmin]BF4 [17], Fe 3+ -montmorillonite [11],… Tuy nhiên, việc sử dụng các loại xúc tác này đòi hỏi thời gian phản ứng dài, sử dụng dung môi hữu cơ khan, điều kiện phản ứng khắc nghiệt, lượng xúc tác rắn được sử dụng nhiều, chất thải sau phản ứng gây độc hại lớn, nhiệt độ phản ứng cao và xúc tác sau khi sử dụng khó thu hồi và tái sử dụng [18][19][20][21].…”