Heteropolyacid-Based Ionic Liquid [HOOCC5H4NH]3PW12O40 as the Eco-Friendly Catalyst for the One-Pot Synthesis of Xanthenediones under Solvent-Free Conditions

In this study, Keggin-type phosphotungstate-based ionic liquid [HOOCC5H4NH](3)PW12O40 was synthetized using nicotinic acid and H3PW12O40 as precursors and characterized via FT-IR, H-1 NMR, C-13 NMR, XRD, TGA, and DTG analyses. Then, [HOOCC5H4NH](3)PW12O40 was utilized as a highly effective and eco-friendly catalyst for the synthesis of xanthenediones through two-component reaction of aldehydes and dimedone under solvent-free conditions at 120 degrees C. The convenient work-up procedure, mild reaction conditions, high yields, and practically short reaction times were the specific merits of the synthetic method. In addition, the designed ionic liquid was recycled efficiently and reused four times without further decrease in the catalytic ability.