Phosphorous acid 70% is used for the manufacture of phosphonates (used in detergents and as water conditioners), inorganic phosphites (used as stabilizers) and for production of agrochemicals and pharmaceuticals. Phosphorous acid is a diprotic acid and an intermediate in the synthesis of other phosphorous compounds. Phosphorous acid is a reducing agent that can be used in the production of phosphonates, phosphite salts, and agricultural chemicals. Upon heating, it is a convenient precursor to phosphine (PH3).