Room temperature ionic liquid choline chloride-oxalic acid: A versatile catalyst for acid-catalyzed transformation in organic reactions

An efficient and facile synthesis of hydrazones, bis(indolyl)methanes and bis(4-hydroxycoumarin)methanes is facilitated by room temperature ionic liquid choline chloride-oxalic acid (ChCl:Ox). ChCl:Ox (10 mol%) efficiently catalyzes condensation of aldehydes with phenylhydrazine giving corresponding hydrazones in high yield (92-96%) within short reaction time of 3-5 min. Electrophilic cyclization reaction of indole and 4-hydroxy coumarin with aromatic aldehyde was effectively promoted by 30 mol% of ChCl:Ox giving corresponding bis(indoly1) arylmethanes and bis (4-hydroxycoumarin)methanes in good yield at room temperature. Procedure is very simple, solvent free and completely eliminates use of toxic acid catalyst. ChCl:Ox is biodegradable, can be recycled and reused without the loss of efficiency with respect to yield. (C) 2013 Elsevier B.V. All rights reserved.