N-sulfonic acid pyridinium -4-carboxylic acid chloride {[Pyridine-N-SO3H-4-COOH]Cl} was synthesized, identified and applied as an effective catalyst for the preparation of pyrido[2,3-d:6,5-d]dipyrimidines by the condensation reaction of various aldehyde with 2-thiobarbituric acid and ammonium acetate under solvent-free conditions.The structure ofcatalyst was studied by various techniques including FT-IR, 1HNMR, 13CNMR, SEM, EDS, TEM, TGA, DTG and XRD analyses. Manuscript profile