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Phosphonic acid (Phosphorous acid)

EC / List no.: 237-066-7

CAS no.: 13598-36-2

Mol. formula: H3O3P

Molecular Weight: 82.00

EC Number: 237-066-7

Phosphonic acid (Phosphorous acid) is a phosphorus oxoacid commonly used as an intermediate in chemical synthesis to produce various phosphorus compounds. 

Phosphonic acid is also used as a strong reducing agent in organic synthesis.

Phosphonic acid 70% is used to make phosphonates for water treatment and oilfield applications and stabilizers for PVC.

Synonyms: PHOSPHOROUS ACID, Phosphonic acid, Orthophosphorous acid

Phosphonic acid produces basic lead phosphonate PVC stabilizer, amino methylene phosphonic acid (ATMP), and hydroxy ethane diphosphonic acid (HEDP).

Phosphonic acid is used as a strong reducing agent.

Phosphonic acid is used to produce raw materials of synthetic fibers, organophosphorus pesticides, etc.

Phosphonic acid is used to produce highly efficient water treatment agent amino trimethylene phosphonic acid.

Phosphonic acid-based fungicides, also called phosphonates, have been used extensively as crop protectants in horticulture since the late 1970s and, more recently in native ecosystems and forestry. 

Discovering that phosphonates are effective against foliar and soilborne oomycete diseases, such as those caused by species of Phytophthora, Pythium, and Plasmopara, was a significant breakthrough, especially for soilborne pathogens that are notoriously difficult to manage. 

Phosphonates have played an essential role in protecting forests and sensitive natural ecosystems under threat from these pathogens. 

Since its introduction, their increased application in managing non-oomycete diseases and other functionalities demonstrate their versatility in agriculture and, more broadly.

Continued use of phosphonic acid crop protectants will be underpinned by demonstrated efficacy and safety and a better understanding of specific interactions within the plant, pathogen, and environment.

Phosphonic acid is also used in the following products: fertilizers, lubricants, and greases.

Phosphonic acid can control diseases caused by pathogens that belong to the Oomycota phylum (or oomycetes) on agronomical and horticultural crops.

Since phosphonic acid was found to be effective against fungal diseases, in particular those caused by oomycetes, the use of its potassium and sodium salts and its ester fosetyl became prevalent in agriculture. 

Phosphonic acid was used as a plant-strengthening agrochemical because it enhances the plant's defense systems against pathogens.

Phosphonic acid, also called Phosphorous acid, is the compound described by the formula H3PO3. 
Phosphonic acid is diprotic (readily ionizes two protons), not triprotic, as might be suggested by this formula. 

Phosphorous acid is an intermediate in the preparation of other phosphorus compounds. 

Organic derivatives of phosphorous acid, compounds with the formula RPO3H2, are called phosphonic acids.

Phosphonic acid (H3PO3), also called orthophosphorous acid, is one of several oxygen acids of phosphorus used as a reducing agent in chemical analysis. 

Phosphonic acid is a colorless or yellowish crystalline substance (melting point about 73° C, or 163° F) with a garlic-like taste. 

An unstable compound that readily absorbs moisture, Phosphonic acid is converted to phosphoric acid (H3PO4) in the presence of oxygen or when heated above 180 °C (360 °F). 

Phosphonic acid (H3PO3) forms salts called phosphites also used as reducing agents. 

Phosphonic acid is prepared in water by dissolving tetra phosphorus hexoxide (P4O6) or phosphorus trichloride (PCl3).

Phosphoric acid (H3PO4) should not be confused with Phosphonic acid (H3PO3). 
A little difference in the name or formula of a chemical compound can make a dramatic difference in its properties. The former is a fully oxidized and hydrated form of P, whereas the latter is a partially oxidized and hydrated form. 

Therefore, Phosphonic acid is a powerful reducing agent, but phosphoric acid is not. 
The former (H3PO4) is a diprotic acid (readily ionizes two protons), but the latter (H3PO3) is a triprotic acid (readily ionizes three protons). 

Phosphonic acid dissociates to form the phosphonate ion (HPO32-), also called phosphite. 

Phosphonic acid and its ionized compounds are often called phosphonate or phosphonite. 

Like phosphate, phosphonate is quickly taken up (Street and Kidder 1989) and translocated inside the plant.

Translated names
acid fosfonic (ro)

acide phosphonique; (fr)

acido fosfonico (it)

Fosfonihappo (fi)

fosfono rūgštis (lt)

fosfonska kislina (1) (sl)

fosfonskābe (lv)

fosfonzuur (nl)

Fosfoonhape (et)

fosforsyrlighet (sv)

fosforsyrling (no)

foszfonsav (hu)

kwas fosfonowy (pl)

kyselina fosforitá (sk)

Phosphonsäure (de)

trihydroxophosphor (da)

àcido fosfónico (es)

ácido fosfónico (pt)

φωσφονικό οξύ (el)

фосфониева киселина (bg)

IUPAC names
acido triossofosforico

Also known as Phosphorous acid




Phosphonic Acid

Phosphonic acid

phosphonic acid

Phosphonic Acid

Phosphonic acid

phosphonic acid

phosphonic acid

Phosphonic acid; Phosphorous acid


Phosphorous acid

phosphorous acid
Phosphorous Acid

Phosphorous acid

Potassium phosphite

triossophosphoric acid(III)

Trade names

Orthophosphorous Acid


Phosphonic acid

phosphonic acid

Phosphorige Säure

Phosphorige Säure min. 98,5 %

Phosphorige Säure min. 99,0 %


Phosphorous acid

Phosphorous Acid (PA)

Phosphorous acid 50%

Phosphorous acid 70%

Phosphorous acid 70% grade

Phosphorous acid 70% solution

Phosphorous acid crystalline

Phosphorous acid flake


phosphorige Saeure
Phosphorous acid, ortho
trioxophosphoric(3-) acid
trihydrogen trioxophosphate(3-)
hydridotrioxophosphoric(2-) acid
dihydrogen hydridotrioxophosphate(2-)

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