PHOSPHOROUS ACID

PHOSPHOROUS ACID

    
CAS No.  13598-36-2

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

SYNONYMS: Phosphonsure; AURORA KA-1076; PHOSPHORUS ACID; PHOSPHONIC ACID; orthophosphorus; ORTHOPHOSPHOROUS; Phosphorous acid; Phospohorous acid; O-PHOSPHOROUS ACID; Trihydroxyphosphine; PHOSPHOROUS ACID; phosphorous; phosphonic; acid; 13598-36-2; CASNO 13598-36-2; CAS NUMBER 13598-36-2; Phosphorous acid; 10294-56-1; Phosphorane, trihydroxy-; Orthophosphorus acid; phosphonophosphonic acid; Caswell No. 663I; trioxophosphate; H3O3P; Phophorous acid; trioxidophosphate; Phosphorous-acid-; UNII-95E079716M; EINECS 233-663-1; UN2834; EPA Pesticide Chemical Code 076002; phosphonate de disodium; phosphonate de potassium; ACMC-1BDTU; Phosphorus Acid, tech grade; KSC148O2L; DTXSID7035511; CHEBI:36361; CTK0E8725; KS-00000WKD; MBF-051; ANW-19996; AKOS024437580; ZINC245189300; EBD2207688; Phosphorous acid [UN2834] [Corrosive]; LS-106401; 95E079716M; FT-0645100; X6457; Q407743; 14939-26-5; 

Chemical formula: H3PO3
Molar mass: 81.99 g/mol
Appearance: White solid
Density: 1.651 g/cm3 (21 °C)
Melting point: 73.6 °C (164.5 °F; 346.8 K)
Boiling point: 200 °C (392 °F; 473 K) (decomposes)
Solubility in water: 310 g/100 mL
Solubility: soluble in ethanol
Acidity (pKa): 1.1, 6.7
Magnetic susceptibility (χ): −42.5·10−6 cm3/mol

Phosphorous acid is the compound described by the formula H3PO3. This 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.
H3PO3 is more clearly described with the structural formula HPO(OH)2. In the solid state, HP(O)(OH)2 is tetrahedral with one shorter P=O bond of 148 pm and two longer P–O(H) bonds of 154 pm. This species exists in equilibrium with an extremely minor tautomer P(OH)3. IUPAC recommends that the latter be called phosphorous acid, whereas the dihydroxy form is called phosphonic acid.[2] Only the reduced phosphorus compounds are spelled with an "ous" ending.
Other important oxyacids of phosphorus are phosphoric acid (H3PO4) and hypophosphorous acid (H3PO2). The reduced phosphorus acids are subject to similar tautomerism involving shifts of H between O and P. Phosphorus acid is used to prepare phosphite salts. It is usually sold as a 20% aqueous solution.
Uses
The most important use of phosphorous acid (phosphonic acid) is the production of basic lead phosphite, which is a stabilizer in PVC and related chlorinated polymers.[3]
It Used in the production of basic lead phosphonate PVC stabilizer, aminomethylene phosphonic acid and hydroxyethane diphosphonic acid. Also used as a strong reducing agent and in the production of raw materials of phosphorous acid, synthetic fibres and organophosphorus pesticides etc. It used in the production of high efficient water treatment agent amino trimethylene phosphonic acid.
Ferrous materials, including steel, may be somewhat protected by promoting oxidation ("rust") and then converting the oxidation to a metalophosphate by using phosphoric acid and further protected by surface coating.

General Description
A white or yellow crystalline solid (melting point 70.1 deg C) or a solution of the solid. Density 1.651 g /cm3 . Contact may severely irritate skin, eyes, and mucous membranes. Toxic by ingestion, inhalation and skin absorption.
Air & Water Reactions
Deliquescent. Absorbs oxygen from the air very readily to form phosphoric acid [Hawley]. Soluble in water.
Reactivity Profile
Phosphorous acid decomposes when heated to form phosphine, a gas that usually ignites spontaneously in air. Absorbs oxygen from the air to form phosphoric acid [Hawley]. Forms yellow deposits in aqueous solution that are spontaneously flammable upon drying. Reacts exothermically with chemical bases (for example: amines and inorganic hydroxides) to form salts. These reactions can generate dangerously large amounts of heat in small spaces. Dissolution in water or dilution of a concentrated solution with additional water may generate significant heat. Reacts in the presence of moisture with active metals, including such structural metals as aluminum and iron, to release hydrogen, a flammable gas. Can initiate the polymerization of certain alkenes. Reacts with cyanide compounds to release gaseous hydrogen cyanide. May generate flammable and/or toxic gases in contact with dithiocarbamates, isocyanates, mercaptans, nitrides, nitriles, sulfides, and strong reducing agents. Additional gas-generating reactions occur with sulfites, nitrites, thiosulfates (to give H2S and SO3), dithionites (to give SO2), and carbonates (to give CO2).
Health Hazard
TOXIC; inhalation, ingestion or skin contact with material may cause severe injury or death. Contact with molten substance may cause severe burns to skin and eyes. Avoid any skin contact. Effects of contact or inhalation may be delayed. Fire may produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may be corrosive and/or toxic and cause pollution.
Fire Hazard
Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive and/or toxic fumes. Some are oxidizers and may ignite combustibles (wood, paper, oil, clothing, etc.). Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated.
Industrial uses
This collector was developed recently and was used primarily as specific collector for cassiterite from ores with complex gangue composition.On the basis of the phosphonic acid, Albright and Wilson had developed a range of collectors mainly for flotation of oxidic minerals (i.e. cassiterite, ilmenite and pyrochlore). Very little is known about the performance of these collectors. Limited studies conducted with cassiterite and rutile ores showed that some of these collectors produce voluminous froth but were very selective.

Phosphorous acid is produced in the form of a white volatile powder by the slow combustion of phosphorus. Its salts are called phosphites. It is conveniently prepared by allowing phosphorous trichloride to react with water. In industrial synthesis PCl3 is sprayed into steam at 190oC the heat of reaction is used to distill off the hydrogen chloride and excess water vapour.

What is phosphorous acid used for?

Phosphoric fatty acid. Phosphoric acid, also known as orthophosphoric acid, (H3PO4), the most essential phosphorus oxygen acid, was used to produce fertilizer phosphate salts. It is also used in dental cements, in albumin derivatives preparation and in the sugar and textile industries.
Why is phosphorous acid stronger than phosphoric acid?

Hydrogen does not pull on electrons as much as oxygen and thus part of the molecule is more positive, creating a stronger dipole moment in phosphoric acid than that. Phosphorous acid has the constant of higher acidity corresponding to a lower pKa value and is thus more acidic than phosphoric acid.
Which acid is h3po3?

H3PO3 is called orthophosphorous acid or phosphorous acid. It is one of the phosphorus oxygenic acids. Phosphorous acid (H3PO3) forms salts known as phosphites which are sometimes used as reduction agents.
What is the basicity of phosphoric acid?

Phosphoric acid baseline, is 3. Basicity of the molecule is the number of acidic hydrogen atoms. To be acidic, hydrogen must be bound to a highly electronegative atom such as oxygen or fluorine.
What are the side effects of phosphoric acid?

Lips, tongue, throat and stomach will burn. Symptoms may include nausea, vomiting, cramps in the stomach and diarrhoea. May results in permanent damage. Long-Term (Chronic) Effects of exposure: At low concentrations: can cause dry, raw, cracking skin (dermatitis) after skin contact.