Phosphorous acid CAS NO.10294-56-1

Synonyms: Orthophosphorous acid; phosphonic acid (IUPAC)
De: Phosphonsäure   ES: Ácido fosfónico   Fr:Acide phosphonique
Molecular Weight: 81.996
Molecular Formula: H3PO3
Structural Formula: 
Density: 1.6510
M.P.: 73.6°C
B.P.: 200°C (decomposing at 180°C)
Physical & Chemical Properties: Phosphorous acid is a white, solid, reducing, diprotic (not triprotic as its formula suggests) acid, hygroscopic and deliquescent. It exists in equilibrium with a minor tautomer P(OH)3, IUPAC recommendations 2005, are that the latter is called phosphorous acid, whereas the dihydroxy form is called phosphonic acid.

Application

1) The most important use of phosphorous acid is to produce phosphonates, for example ATMP, HEDP, PBTC which are used as scale inhabitor or corrosive inhabitor in water treatment, and PMIDA (CAS 5994-61-6) which is a very important intermediate of herbicide glyphosate. 
2) Phosphorous acid is also used for preparing phosphite salts, such as potassium phosphite, ammonium phosphite and calcium phosphite. These salts, as well as aqueous solutions of pure phosphorous acid, have shown effectiveness in controlling a variety of microbial plant diseases, in particular, treatment using either trunk injection or foliar containing phosphorous acid salts is indicated in response to infections by phytophthora and pythium-type plant pathogens (both within class oomycetes, known as water molds), such as dieback/root rot and downy mildew. Anti-microbial products containing salts of phosphorous acid are marketed in Australia as 'Yates Anti-Rot'; and in the United States of America, for example, aluminum salts of phosphorous acid (known generically as 'Fosetyl-Al') are sold under the trade name 'Aliette'. Another important phosphite salt is lead phosphite dibasic which is used as PVC stabilizer. 
3) Phosphorous acid is also used in chemical reactions as a reducing agent that is somewhat less vigorous than the related hypophosphorous acid. 
4) Upon heating to around 200 °C, it is a convenient precursor to phosphine: 4H3PO3 → PH3 + 3H3PO4

Specification*

Standard Packaging