Brönsted Acid-Surfactant-combined Ionic Liquid Catalyzed Green Synthesis of 2-Alkyl and 2-Arylbenzothiazoles in Water: Reusable Catalyst and Metal-Free Conditions

An efficient Brönsted acid-surfactant-combined ionic liquid (BASILs) catalyzed cyclocondensation of 2-aminothiophenol with a variety of aldehydes in water is described. This protocol was successfully conducted under metal-free conditions at ambient temperature and produced 2-alkyl and 2-arylbenzothiazole products in high to excellent yields (up to 98%). The catalyst was reusable at least four times without significant loss of activity.