phosphonic acid

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A colourless to pale-yellow deliquescent crystalline solid, H3PO3; r.d. 1.65; m.p. 73.6°C; decomposes at 200°C; very soluble in water and soluble in alcohol. Phosphonic acid may be crystallized from the solution obtained by adding ice-cold water to phosphorus(III) oxide or phosphorus trichloride. The structure of this material is unusual in that it contains one direct P-H bond and is more correctly written (HO)2HPO. The acid is dibasic, giving rise to the ions H2PO3 and HPO32− (phosphonates; formerly phosphites), and has moderate reducing properties. On heating it gives phosphine and phosphoric(V) acid.

Subjects: Chemistry.

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