Melaminium Tris Dihydrogen Phosphate (MTDP): A New Green and Sustainable Tricationic Ionic Liquid Catalyst for the Knoevenagel Synthesis of 5-Arylidene(thio)barbituric Acids in Water

This study focuses on the preparation and characterization of melaminium tris dihydrogen phosphate (MTDP), a tricationic Brønsted acidic ionic liquid, through various advanced analytical techniques, including FT-IR, ¹H, ¹³C NMR and ³¹P NMR spectroscopies within a full comparative study between the TGA/DTG diagrams of melamine and MTDP. Following its comprehensive identification, MTDP was employed as an efficient and recyclable catalytic agent in the synthesis of 5-arylidene (thio)barbituric acid derivatives. The proposed methodology offers several notable advantages, such as high product yields (84–95%), rapid reaction rates (5–13 minutes), mild reaction conditions, and the utilization of low amounts of environmentally benign, non-toxic reagents (2 mol%).