Facile synthesis of bis(indolyl)methanes over cordierite honeycomb coated with modified forms of zirconia under microwave irradiation condition

Abstract

Zirconia (ZrO₂), Mo(VI)/ZrO₂, W(VI)/ZrO₂ and SO₄^2-/ZrO₂ have been coated on honeycomb monoliths and used as catalytic material in the microwave-assisted synthesis of various bis(indolyl)methane derivatives via condensation. These catalytic materials have been characterized for their properties such as surface acidity, crystallinity, morphology and elemental analysis by suitable techniques. A correlation between the acidity, crystallinity and the catalytic activity of these catalytic materials is observed. The effect of conventional heating and microwave heating on the synthesis of these derivatives has been studied. Microwave-assisted synthesis of bis(indolyl)methane derivatives over zirconia and its modified forms is found to be a fast and facile catalytic route. Up to 98% yield of bis(indolyl)methanes is obtained in a very short reaction time of 4 min under microwave irradiation, whereas it requires 20 min to obtain 98% yield under conventional heating. The honeycomb monoliths coated with modified forms of zirconia as catalytic materials are efficient, easily reactivable and reusable for at least six reaction cycles.