Synthesis of silica chemisorbed bis(hydrogensulphato)benzene (SiO2–BHSB) as a new hybrid material and it's utility as an efficient, recyclable catalyst for the green synthesis of bis(indolyl)methanes

Abstract

Synthesis of silica chemisorbed bis(hydrogensulphato)benzene (SiO2-BHSB) was achieved as a new hybrid catalytic material, its structure, stoichiometry and stability was established using modern analytical techniques such as CP-MAS 13C NMR, CP-MAS 29Si NMR, EDX, FT-IR, TGA and DTG. The synthesised material SiO2–BHSB was observed as an environmentally benign, recyclable catalyst for the synthesis of bis(indolyl)methanes (BIMs) via an electrophilic substitution reaction of indoles by aldehydes or ketones under solvent free grinding condition. A range of structurally diverse aldehydes, ketones and indoles were smoothly undergone the developed catalytic protocol to offer good to excellent yields of corresponding bis(indolyl)methane derivatives in shorter reaction times. The synthesised material SiO2–BHSB showed a sustained catalytic activity up to five cycles of its reuse for the synthesis of BIMs. The catalytic protocol offered a chemo-selective route for the synthesis of BIMs, in which aldehydes are pushed exclusively in presence of ketones to undergo the reaction. Simple working procedure, ease of isolation of the catalyst, environmentally compatible energy conditions and no side products are the additional salient features of this protocol.