7346. Phosphorous Acid

Nomenclature

CAS number: 13598-36-2
Phosphonic acid.
H3O3P; mol wt 82.00.
H 3.69%, O 58.53%, P 37.77%.

Description and references

Prepd by hydrolysis of PCl3 according to the equation PCl3 + 3H2O → H3PO3 + 3HCl, the rather violent reaction can be slowed down by the initial presence of concd HCl: Milobedzki, Friedmann, Chem. Pol. 15, 76 (1917); Chem. Z. 1918, I, 933; Simon, Fehér, Z. Anorg. Allg. Chem. 230, 298 (1937). Alternate procedure carrying out the reaction in carbon tetrachloride: Voight, Gallais, Inorg. Synth. 4, 55 (1953). Review: Ohashi, “Lower Oxo Acids of Phosphorus and Their Salts” in Topics in Phosphorus Chemistry Vol. 1, M. Grayson, E. J. Griffith, Eds. (Interscience, New York, 1964) pp 113-187.

Chemical structure

Properties

White, very hygroscopic and deliquesc, crystalline mass; garlic-like taste; slowly oxidized by oxygen (air) to H3PO4. d421 1.65; d476 liq 1.597. mp ≈73°; above 180° is dec into PH3 and H3PO4. Very sol in water, alcohol. pK1 1.29; pK2 6.74. Usually marketed as a 20% aq soln.