<p>Selective solubility of a catalyst can be an advantage to easily separation the catalyst from reaction media after the reaction is complete. Two phosphoric acid-based organic salts with selective solubility were prepared by stirring 4,4ʹ-trimethylenedipiperidine (TMDP) with phosphoric acid (PA) (85 wt.%) at two different mole ratios of 1:1 and 1:2. The chemical structure of the products was characterized using spectroscopic techniques, including ³¹P NMR, which demonstrated the formation of two distinct phosphoric-based organic salts. The melting point of products using a capillary tube in ambient conditions and the DSC profile in the nitrogen atmosphere confirmed that both products were molten salts (melting points &gt; 100&#xa0;°C), contrary to a previous report. The detailed spectroscopic data, physical properties, and thermal behavior of new phosphoric acid-based organic salts were recorded and reported for the first time. Due to the abundance of active sites for donor and acceptor hydrogen bonds and their insolubility in organic solvents, even methanol and ethanol, as-prepared organic phosphoric acid-based salts were utilized as hydrogen bond catalysts in a multicomponent reaction to prepare pyrrolidinone scaffolds. A 100% conversion was achieved in the reaction using only 35&#xa0;mg of TMDP-PA (1:2) and TMDP-PA (1:1) per 1&#xa0;mmol of the substrate at 60&#xa0;°C within 65 and 95&#xa0;min, respectively. The substrate scope of the current catalytic protocol was explored using TMDP-PA (1:2), resulting in good to excellent products using a catalytic amount of TMDP-PA (1:2). Both molten salts exhibited high recyclability, and the recovered catalysts were successfully reused in consecutive runs without significant loss of activity. This study highlights the effectiveness of two new phosphoric acid-based organic salts as heterogeneous catalysts for organic synthesis.</p>