Ammonium phosphinate is a chemical compound with the chemical formula . This is a salt of ammonium and phosphoric acid. Synthesis. The effect of ammonia solution on phosphoric acid solution: Physical properties. Ammonium phosphonate forms colorless crystals of rhombic system, spatial group "C mma", cell parameters a = 0.757 nm, b = 1.147 nm, c = 0.398 nm, Z = 4. The compound is soluble in water and ethanol, but insoluble in acetone. Uses. The compound is usually used as a catalyst for the production of polyamide.