Cu/Cu₂O@g‐C₃N₄: Recyclable Photocatalyst under Visible Light to Access 2‐Aryl‐/benzimidazoles/benzothiazoles in Water

Abstract

An unprecedented Cu/Cu2O@g‐C3N4 catalysed visible light driven green synthesis of 2‐aryl‐/benzimidazoles and benzothiazoles is reported via condensation of structurally different aldehydes with o‐phenylenediamine and o‐aminothiophenol respectively. Herein, Synergistic catalysis is operating as both Cu/Cu2O@g‐C3N4 and visible‐light condition are required, no product was isolated in absence of either. Operational simplicity, ambient reaction conditions, aqueous medium, good yield of products (80–94 %) and recyclability of the catalyst without any loss in catalytic efficiency and selectivity are salient features of the envisaged protocol.

Progress in Photocatalytic Synthesis of Benzimidazoles

“…Most of the results suggested that the photocatalytic conversion process was well compatible with the substituents no matter they are electron‐withdrawing or ‐releasing groups, such as −OH, −Cl, −Br, −NO 2 . They had little effect on the yield of BIs [15,37,43] . Some other studies showed that the activity of aromatic aldehydes with electrophilic substituents was slightly higher than that with electron‐donating substituents [16–17,23,42] .…”

“…The high activity observed in MeCN may ascribe to the stabilization of the photoinduced radicals by MeCN. In addition, Singh's work [43] indicated that the yield of BIs was proportional to the polarity of the solvent and decreased in order of water> ethanol> MeCN. The reaction performed in non‐polar toluene showed no yield of BIs.…”

“…g‐C 3 N 4 is a metal‐free polymer semiconductor with high photocatalytic activity under visible light. Singh et al [43] . reported the photocatalytic synthesis of BIs based on g‐C 3 N 4 for the first time.…”

“… Photocatalytic synthesis of BIs based on (a) CdSe/MMT, [41] (b) CBTH, [42] and (c) Cu/Cu 2 O@C 3 N 4 [43] …”

“…Furthermore, it should be pointed out that some works [15,41–43] showed that the developed reaction system was not only suitable for the synthesis of BIs, but also was competent for the preparation of benzothiazole with only changing OPDA to o‐aminothiophenol. Moreover, the conversion was easier to proceed than the preparation of BIs in short illumination time.…”