Sulfonated Organic Heteropolyacid Salts: Recyclable Green Solid Catalysts for the Highly Efficient and Green Synthesis of Bis(indolyl)methanes in Water

In the present study, we introduce two nonconventional ionic liquids [MIMPS]3PW12O40 (a) and [TEAPS]3PW12O40 (b) as green solid acid catalysts for the efficient synthesis of bis(indolyl)methanes. The reaction of indole with aldehydes or ketones in water afforded the corresponding bis(indolyl)methanes in excellent yields. This reaction has been carried out in the presence of 1 mol% of catalysts at room temperature. The reusability of the catalysts was demonstrated by a six-run test. Additionally, the catalysts pose several advantages including mild reaction conditions, cleaner reactions and shorter reaction times.