Cellulose sulfuric acid: reusable catalyst for solvent-free synthesis of bis(indolyl)methanes at room temperature

Bis(indolyl)methanes were synthesized from indole and aldehydes under solvent-free conditions using cellulose sulfuric acid (CSA) as a catalyst at room temperature. CSA is easily prepared and it was also found that this catalyst could be recovered quantitatively and reused without much loss of catalytic activity.