Synthesis, characterization and application of nano-silica@[DPSSP][Cl]₂ as a novel organic–inorganic hybrid catalyst for the rapid condensation of aldehyde, ammonium acetate and thiobarbituric acid

At first, the preparation and identification of a novel heterogeneous organic–inorganic hybrid acidic nanocatalyst, namely 1,3-(4-pyridyl-1-ium sulfonic acid) (4′-pyridyl-1-ium silica-n-propyl)-propane-dichloride grafted on nano-silica (nano-silica@[DPSSP][Cl]₂), have been reported; the identification has been done through a broad range of physicochemical methods comprising FT-IR, SEM, HRTEM, BET, TGA, XRD and EDX techniques. Afterward, nano-silica@[DPSSP][Cl]₂ was successfully applied to facilitate the condensation of aryl aldehydes (1 mmol), 2-thiobarbituric acid (2 mmol) and NH₄OAc (1.4 mmol) in water solvent (2 mL) at room temperature, such that it provided ten derivatives of pyrido[2,3-d:6,5-d']dipyrimidines (1a–10a) in 5–10 min with yields of 93–99%. Our catalyst furnished the derivatives in very short reaction times and in excellent yields, high atom economy, easy workup and very favorable turnover number (TON) and turnover frequency (TOF) values. In addition, the heterogeneous nature of the catalyst was confirmed and measured using the hot filtration test and its excellent reusability in six runs. Graphical abstract: [Figure not available: see fulltext.]