Ionic liquid coated sulfonated carbon@titania composites for the one-pot synthesis of indeno[1,2-b]indole-9,10-diones and 1H-pyrazolo[1,2-b]phthalazine-5,10-diones in aqueous media

A highly active and stable ionic liquid based novel solid Bronsted acid catalyst (C@TiO2-SO3H-ILs) was prepared by coating a long chain ionic liquid onto sulfonated carbon@titania composites. The ionic liquid coating resulted in efficient stability and activity of C@TiO2-SO3H-ILs under aqueous conditions by creating a hydrophobic environment on the catalyst surface. The catalytic activity of the newly designed catalyst was tested in the one-pot multicomponent synthesis of indeno[1,2-b]indole-9,10-diones and 1H-pyrazolo[1,2-b]phthalazine-5,10-diones in aqueous media. The structure of the most active catalyst, C@TiO2-SO3H-IL1, before and after the coating with the ionic liquid was investigated by FTIR, TGA, XRD, CHNS, EDX, SEM and HRTEM. The catalyst allows easy recovery and excellent reusability for up to five catalytic runs without considerable loss of activity.