Product show

Phosphorous Acid


Synonyms: Orthophosphorous acid; phosphonic acid (IUPAC)
De: Phosphonsäure   ES: Ácido fosfónico   Fr:Acide phosphonique
CAS No.: 13598-36-2   EC No.: 233-663-1   RTECS No.: SZ6400000
Molecular Weight: 81.996
Molecular Formula: H3PO3
Structural Formula: phosphorous acid
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.


1) Phosphorous acid is product of hydrolysis of its acid anhydride: P4O6 + 6 H2O → 4 HPO(OH)2
2) On an industrial scale, phosphorous acid is prepared by hydrolysis of phosphorus trichloride with water or steam: PCl3 + 3 H2O → HPO(OH)2 + 3HCl
3) Potassium phosphite is also a convenient precursor to phosphorous acid:
K2HPO3 + 2 HCl → 2 KCl + H3PO3
In practice aqueous potassium phosphite is treated with excess hydrochloric acid. By concentrating the solution and precipitations with alcohols, the pure acid can be separated from the salt.


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


  Grade II Grade III Grade IV 70% Solution
Phosphorous acid Purity 99.0% min. 98.5% min. 98.5% min. 70% min.
Chloride (Cl) 10ppm max. 0.01% max. 0.01% max. 0.01% max.
Iron(Fe) 10ppm max. 30ppm max. 50 ppm max. 10ppm max.
Sulfate(SO4) 10ppm max. 80ppm max. 80 ppm max. 80ppm max.
Phosphate (PO4) 0.1% max. 0.2% max. 0.3% max. 0.1% max.
Color,70% solution colorless colorless colorless colorless
Odor odorless odorless odorless odorless
Appearance white crystals white crystals white crystals clear colorless liquid

Standard Packaging

1)  25kgs per PP woven bag with two PE inner bags, 19~27mt per 20’ FCL
2) For packaging 500 or 1000kgs/supper bag, maximum loading in 20’ FCL : 20000kg
3) 50kg per iron drum or plastic drum
4) 70% solution: 25kg or 250kg per plastic drum, or 1300kg per 1000L IBC

packaging of phosphorous acid

Risks and Safety Information

Class 8; UN 2834; PG III. Corrosive Acid, Dangerous.
R 22 Harmful if swallowed. R 35 Causes severe burns.
S 26 In case of contact with eyes, rinse immediately with plenty of water and seek medical advice.
S 36/37/39 Wear suitable protective clothing, gloves and eye/face protection.
S 45 In case of accident or if you feel unwell, seek medical advice immediately (show the label where possible).

warning corrosive

Related Products