Synthesis of Benzoxazoles, Benzimidazoles, and Benzothiazoles Using a Brønsted Acidic Ionic Liquid Gel as an Efficient Heterogeneous Catalyst under a Solvent-Free Condition

Abstract

Herein, we introduce a reusable Brønsted acidic ionic liquid gel (BAIL gel) obtained by treating 1-methyl-3-(4-sulfobutyl)-1H-imidazolium hydrogen sulfate with tetraethyl orthosilicate (TEOS). The grafting of the Brønsted acidic ionic liquid to the surface of TEOS has increased the catalytic activity of the material and also simplified catalyst recovery from the reaction mixture. This reaction has a wide substrate scope, and the BAIL gel represents a new catalyst for the synthesis of benzoxazoles, benzimidazoles, and benzothiazoles. The method shows attractive characteristics such as high yields, recyclable catalyst, and work-up simplicity. More importantly, no additional additives or volatile organic solvent and inert atmosphere are required for the reaction, and the BAIL gel has shown a great promise for industrial applications. To the best of our knowledge, the synthesis of benzoxazoles, benzimidazoles, and benzothiazoles using a recyclable heterogeneous ionic liquid gel was not previously reported in the literature.