Self-assembled alkyl imidazolium based organosilica as efficient support for sulfonic acid catalyst in the synthesis of bis(indolyl)methanes

Abstract

A novel sulfonic acid-containing hybrid organic–inorganic material with ionic liquid framework (IL-OS-SO3H) is prepared, characterized and applied as efficient catalyst for the synthesis of bis(indolyl)methanes. The IL-OS-SO3H was prepared through hydrolysis and condensation of 1,3-bis(3-trimethoxysilylpropyl)imidazolium iodide followed by grafting of 3-thiopropyl-trimethoxysilane and then oxidation of SH groups in the presence of hydrogen peroxide. This catalyst was characterized using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The IL-OS-SO3H was successfully applied as powerful and reusable catalyst for synthesis of bis(indolyl)methanes at room temperature under solvent-free conditions. This novel catalyst could be recovered and reused at least eight times without significant decrease in catalytic activity and product selectivity.