Solvent-free synthesis of Aryl-3, 3′-bis (indolyl) methanes using KAl(SO4)2·12H2O–anhydrous Na2SO4

An efficient pathway for the synthesis of aryl-3,3'-bis(indolyl)methanes (BIMs) from indole/2- methylindole and aromatic aldehyde(s) is described. The aromatic electrophilic substitution reactions of indole with aromatic aldehydes are achieved in the presence of a mixture of potash alum-anhydrous sodium sulphate under solvent-free conditions at room temperature in the absence of light in excellent yields, and in a shorter reaction time.