Xanthan sulfuric acid: An efficient and biodegradable solid acid catalyst for the synthesis of bis(indolyl)methanes under solvent-free conditions

Xanthan sulfuric acid (XSA) is found to be an efficient catalyst for the electrophilic substitution reaction of indole with aromatic aldehydes to afford the corresponding bis(indolyl)methanes at room temperature under solvent-free conditions. The catalyst was characterized for the first time with the help of powder XRD, SEM–EDX and DSC–TGA. The attractive features of this green, new methodology are excellent yield of products, clean reaction profile, reusability of the catalyst, energy sustainable protocol, simple experimental and easier work-up procedures.

Graphical abstractXanthan sulfuric acid (XSA) is found to be an efficient and recyclable, heterogeneous catalyst in promoting reactions of aldehydes (2a–h) and indole (1) to afford a series of bis(indolyl)methanes (3a–h) in excellent yields. The catalyst was active up to four cycles and was characterized by XRD, SEM-EDX and DSC-TG analyses.Figure optionsDownload full-size imageDownload as PowerPoint slide