Brønsted acidic ionic liquids promoted cyclocondensation reaction: Synthesis of 1,8-dioxo-octahydroxanthene

Novel Brønsted acidic ionic liquids bearing hydrogen sulfate and dihydrogen phosphate as anions were designed and successfully applied as catalysts for the one-pot synthesis of 1,8-dioxo-octahydroxanthene in water medium. The sequence of the catalytic activity observed in the transformation was in good agreement. In this article, six different ionic liquids (ILs) such as, [BMIM][BF4], [CMIM][HSO4], [NMP][HSO4], [BMIM][HSO4], [(CH2)4SO3HMIM][HSO4], [BMIM][H2PO4] were synthesized and used as a catalyst for synthesis of 1,8-dioxo-octahydroxanthene very first time. The products could be conveniently separated from the reaction mixture by filtration and the dissolved catalyst can be regenerated and recycled several times without significant loss of activity.