DABCO-based ionic liquids: green and recyclable catalysts for the synthesis of barbituric and thiobarbituric acid derivatives in aqueous media

Abstract

A new and straightforward method for the synthesis of 5-arylidine barbituric and thiobarbituric acids through a reaction between barbituric acid and its thio-analogue with aldehydes using 1,4-disulfo-1,4-diazabicyclo[2.2.2]octane-1,4-diium dihydrogen sulfate ([DABCO](SO₃H)₂(HSO₄)₂) as an efficient catalyst has been reported. In this project, also the preparation of pyrano[2,3-d]-pyrimidinediones via the reaction of barbituric or thiobarbituric acid, malononitrile and aldehydes in the presence of this reagent and 1,4-disulfo-1,4-diazabicyclo[2.2.2]octane-1,4-diium chloride ([DABCO](SO₃H)₂(Cl)₂) has been investigated. The structure of the products was characterized using IR, ¹H NMR and ¹³C NMR spectroscopy. The present methodologies suggests several advantages such as ease of the preparation and handling of the catalysts, high yields, simple and green procedures, low cost, short reaction times, easy work-up and preformation of the reaction in water as a green solvent.