phosphite

chemical compound

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July 23, 2026

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Phosphite refers to salts or esters of phosphorous acid. Phosphorous acid (H₃PO₃) is a chemical compound prepared by the hydrolysis of phosphorus trichloride. It is a crystalline solid that melts at 70.1 °C and is soluble in water, possessing a garlic-like odor.12

Phosphorous acid and its salts act as reducing agents, readily oxidizing to phosphoric acid and phosphate salts, respectively. For instance, phosphorous acid can reduce silver ions to elemental silver. Structurally, phosphorous acid has two acidic hydrogen atoms bonded to oxygen, making it a diprotic acid, and one hydrogen atom directly bonded to phosphorus. This structure allows it to form two series of salts: dihydrogen phosphite (H₂PO₃⁻) and hydrogen phosphite (HPO₃²⁻). Hypophosphorous acid (H₃PO₂) is another related compound, which is monoprotic and forms hypophosphite salts.23

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oxyacid
Phosphorous acid and phosphite salts
Pure phosphorous acid, H₃PO₃, is best prepared by hydrolysis of phosphorus trichloride, PCl₃.PCl₃ + 3H₂O → H₃PO₃ + 3HCl The resulting solution is heated to drive off the HCl, and the remaining water is evaporated until colourless crystalline H₃PO₃
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Pure phosphorous acid, H₃PO₃, is best prepared by hydrolysis of phosphorus trichloride, PCl₃.PCl₃ + 3H₂O → H₃PO₃ + 3HCl The resulting solution is heated to drive off the HCl, and the remaining water is evaporated until colourless crystalline H₃PO₃
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