Efficient, Rapid, and Solvent-Free Synthesis of Substituted Bis(indolyl)methanes Using Sulfated Anatase Titania as a Solid Acid Catalyst

A rapid and solvent-free green synthesis of bis(indolyl)methanes using sulfated anatase titania (TiO₂-SO₄²⁻) as solid acid catalyst under simple physical grinding has been developed. The advantage of this method is short reaction time with excellent yield and safety, inexpensive cost, and use of easily recyclable nanocatalytic material. Higher activity of sulfated titania over TiO₂ is found to be due to its increased Brønsted acidity.