PHOSPHINIC ACID

Phosphinic acid is a phosphorus oxyacid and a powerful reducing agent with molecular formula H3PO2. 
Phosphinic acid is a colorless low-melting compound, which is soluble in water, dioxane, and alcohols. 
The formula for Phosphinic acid is generally written H3PO2, but a more descriptive presentation is HOP(O)H2, which highlights its monoprotic character. 
Salts derived from Phosphinic acid are called hypophosphites.

CAS Number: 6303-21-5
EC Number: 228-601-5
IUPAC Name: phosphinic acid
Chemical Formula: H3PO2

Other names: RefChem:929168, DTXCID401012094, 228-601-5, 6303-21-5, 8B1RL9B4ZJ, CHEBI:29031, DTXSID90873902, Hydroxyphosphine oxide, Hypophosphorous acid, Hypophosphorus acid, NSC-41904, Phosphine oxide, hydroxy-, Phosphinic Acid, 6303-21-5 [RN], Acide phosphinique [French] [ACD/IUPAC Name], H2PO(OH) [Formula], Phosphinic acid (VAN), PH2(OH)O [Formula], PH2O(OH) [Formula], Phosphinic acid [ACD/Index Name] [ACD/IUPAC Name], Phosphinsäure [German] [ACD/IUPAC Name], [PH2(OH)O], [PH2O(OH)], dihydridodioxophosphoric acid, dihydridohydroxidooxidophosphorus, dihydroxyphosphanium, dihydroxyphosphonium, H3PO2, HPA, hydrophosphorous acid, Phosphinic acid solution, MFCD02183592 [MDL number], UNII-8B1RL9B4ZJ

Phosphinic acid exists in equilibrium with the minor tautomer HP(OH)2. 
Sometimes the minor tautomer is called Phosphinic acid and the major tautomer is called phosphinic acid.

Phosphinic acid is a phosphorus oxoacid that consists of a single pentavalent phosphorus covalently bound via single bonds to two hydrogens and a hydroxy group and via a double bond to an oxygen. The parent of the class of phosphinic acids.

Phosphinic acid has role antioxidant 
Phosphinic acid is a phosphinic acids 
Phosphinic acid is a phosphorus oxoacid 
Phosphinic acid is conjugate acid of phosphinate 

Phosphinic acid is a phosphorus oxoacid that consists of a single pentavalent phosphorus covalently bound via single bonds to two hydrogens and a hydroxy group and via a double bond to an oxygen.
The parent of the class of phosphinic acids. 
Phosphinic acid has a role as an antioxidant. 
Phosphinic acid is a phosphorus oxoacid and a member of phosphinic acids. It is a conjugate acid of a phosphinate.

Phosphinic acid is an important chemical product with wide applications in pharmaceuticals and electroless plating.

Phosphinic acid Uses
Phosphinic Acid is used as a bleaching or decolorizing agent for plastics, synthetic fibers, and chemicals

Phosphinic acid is used as a decolorizing agent and for color stabilization during the manufacture of chemicals and several plastics including: nylon fibers, polyamides, polyester fiber, polyacrilonitrile, alkyd rsins, epoxies, fatty acid esters, and glycerols.

Phosphinic Acid is used in the production of Hypophosphite Salts (i.e., Calcium, Magnesium, Manganese, Potassium, Iron, and Ammonium) which are in turn used in synthetic fibers as wetting dispersing, emulsifying, and anti-static agents

Phosphinic Acid is used in organic synthesis and organo phosphinic acid production
Phosphinic Acid is used as a moderately strong monobasic acid
Phosphinic Acid is a polymerization and polycondensation catalyst
Phosphinic Acid is a as a wetting, dispersing, or emulsifying agent in electroplating

Phosphinic Acid may be used for its strong but slow reducing action
Phosphinic Acid may be used as an antioxidant
Phosphinic acid may be used as a stimulant in pharmaceuticals
Phosphinic acid is used as a chain transfer agent in aqueous polymerizations.
Phosphinic acid has color stabilizer function, antioxydant property and it is also used as reducer or catalyst in multiple industries.

Uses: Phosphinic acid is used in the formulation of pharmaceuticals, discoloration of polymers, water treatment, retrieval of precious or non-ferrous metals. 
Its main use is for electroless plating, i.e. deposition of metal films from solution. 
In organic chemistry, H3PO2 best known for their use in the reduction of arenediazonium salts, converting ArN2+ to Ar-H.

When diazotized in a concentrated solution of Phosphinic acid, an amine substituent can be removed from arenes, selectively over alkyl amines.
Phosphinic Acid (HPA) is also known as phosphinic acid, hydroxy(oxo)-λ5-phosphane, oxo-λ5-phosphinous acid and oxo-λ5-phosphanol. 
Its molecular formula is H3PO2 or HOP(O)H2. Phosphinic acid is a hydroxy phosphine oxide or phosphorus oxyacid having a monobasic character. Phosphinic Acid is a low-melting colorless compound, which is highly soluble in alcohols, dioxane and water. Phosphinic acid is majorly manufactured from Sodium Hypophosphite.

Phosphinic Acid is widely used as a reducing agent to reduce Cu, Hg and Ag etc. to verify impurities, such as Nb, As and Ta, etc. 
It is also used as a catalyst during esterification and in medicines, it is used to detect tellurium and arsenic, etc
Phosphinic Acid is used as a decolorizing or bleaching agent in plastics, chemicals and synthetic fibers. 

It is also used as a color stabilizer during the manufacturing of chemicals and plastics, including polyamides, nylon fibers, polyacrilonitrile, polyester fiber, epoxies, glycerols, fatty acid esters and alkyd resins.
Phosphinic Acid is also used as a polycondensation and polymerization agent, reducing agent, an antioxidant and stimulant in pharmaceuticals, etc. 
Thus, due to the wide areas of application of Phosphinic acid, its consumption is expected to grow at a significant rate during the forecast period.

Phosphinic Acid is used in various end use industries, such as building and construction, electronics and electrical, chemical and plastics, etc. 
Thus, owing to the growing use of Phosphinic Acid in various industries, its sales is expected to increase, thereby propelling the growth of the global Phosphinic Acid market during the forecast period.
Phosphinic Acid is significantly used as a salt (sodium hypophosphite) and also in electroless nickel plating (Ni–P), as well as Phosphinic Acid is also used for reducing arenediazonium salts. 

Though Phosphinic Acid finds application in chemical industry but owing to the ill effects of Phosphinic Acid the United States Drug Enforcement Administration has assigned Phosphinic Acid and its salts in List I precursor chemical and Phosphinic Acid handlers are ordered to keep a record and registration etc. for during the import and export

Melting point: 26.5 °C (79.7 °F; 299.6 K)
Boiling point: 130 °C (266 °F; 403 K) decomposes
Solubility in water: miscible
Solubility: very soluble in alcohol, ether
Acidity (pKa): 1.2
Conjugate base: Phosphinate

Applications: Phosphinic Acid is primarily used for electroless nickel plating. It is involved in the reduction of arenediazonium salts. It acts as an additive in Fischer esterification reactions. Also, it serves as a neutralizing agent, antioxidant, catalyst in polymerization and poly condensation, and wetting agent. Further, it is used in the formulation of pharmaceuticals, discoloration of polymers, water treatment and retrieval of precious or non-ferrous metals. In addition to this, it is used as bleaching agents for plastics, synthetic fibers, decolorizing agent and for color stabilization during the manufacture of chemicals and several plastics.

Notes
Incompatible with strong oxidizers, mercuric oxide, mercury(II) nitrate, metals and strong bases.
Preparation and availability Phosphinic Acid was first prepared in 1816 by the French chemist Pierre Louis Dulong (1785–1838).

The acid is prepared industrially via a two step process: Firstly, hypophosphite salts of the alkali and alkaline earth metals result from the reaction of white phosphorus with hot aqueous solution of the appropriate hydroxide, e.g. Ca(OH)2.

P4 + 4 OH− + 4 H2O → 4 H2PO−2 + 2 H2
The salt is then treated with a strong, non-oxidizing acid to give the free Phosphinic acid:

H2PO−2 + H+ → H3PO2
HPA is usually supplied as a 50% aqueous solution. 
Anhydrous acid cannot be obtained by simple evaporation of the water, as the acid ready oxidises to phosphorous acid and phosphoric acid and also disproportionates to phosphorous acid and phosphine. 
Pure anhydrous Phosphinic acid can be formed by the continuous extraction of aqueous solutions with diethyl ether.

Reactions and uses
Its main industrial use is for electroless nickel plating (Ni–P), although it is primarily used as a salt (sodium hypophosphite).
Phosphinic Acid can reduce chromium(III) oxide to chromium(II) oxide:

H3PO2 + 2 Cr2O3 → 4 CrO + H3PO4

Organic chemistry
In organic chemistry, H3PO2 can be used for the reduction of arenediazonium salts, converting ArN+2 to Ar–H.
When diazotized in a concentrated solution of Phosphinic acid, an amine substituent can be removed from arenes.

Owing to its ability to function as a mild reducing agent and oxygen scavenger it is sometimes used as an additive in Fischer esterification reactions, where it prevents the formation of colored impurities.

Phosphinic acid is used to prepare phosphinic acid derivatives.

DEA List I chemical status
Because Phosphinic acid can reduce elemental iodine to form hydroiodic acid, which is a reagent effective for reducing ephedrine or pseudoephedrine to methamphetamine, the United States Drug Enforcement Administration designated Phosphinic acid (and its salts) as a List I precursor chemical effective November 16, 2001.[12] Accordingly, handlers of Phosphinic acid or its salts in the United States are subject to stringent regulatory controls including registration, recordkeeping, reporting, and import/export requirements pursuant to the Controlled Substances Act and 21 CFR §§ 1309 and 1310.

Phosphinic acid
Main article: Phosphinate
Organophosphinic acids have the formula R2PO2H. The two hydrogen atoms directly bound to phosphorus in phosphinic acid are replaced by organic groups. 
For example, formaldehyde and H3PO2 react to give (HOCH2)2PO2H. 
Similarly, phosphinic acid adds to Michael acceptors, for example with acrylamide it gives H(HO)P(O)CH2CH2C(O)NH2. 
The Cyanex family of dialkylphosphinic acids are used in hydrometallurgy to extract metals from ores.

Inorganic derivatives
Few metal complexes have been prepared from H3PO2, one example is Ni(O2PH2)2.

Phosphinic Acid is a phosphorus oxoacid and a powerful reducing agent. Inorganic chemists refer to the free acid by this name (also as "HPA") although its official IUPAC name is phosphinic acid. See Phosphinic acid. It is a colorless low-melting compound, which is soluble in water, dioxane, and alcohols. The formula for Phosphinic acid is generally written H3PO2, but a more descriptive presentation is HOP(O)H2 which highlights its monoprotic character. Salts derived from this acid are called hypophosphites.

HOP(O)H2 exists in equilibrium with the minor tautomer HP(OH)2. Sometimes the minor tautomer is called Phosphinic acid and the major tautomer is called phosphinic acid.

Preparation and availability
The acid is prepared industrially via a two step process. Hypophosphite salts of the alkali and alkaline earth metals result from treatment of white phosphorus with hot aqueous solution of the appropriate hydroxide, e.g. Ca(OH)2.

UsesPhosphinic Acid is used in the formulation of pharmaceuticals, discoloration of polymers, water treatment, retrieval of precious or non-ferrous metals. 
Its main use is for electroless plating, i.e. deposition of metal films from solution. 
In organic chemistry, H3PO2 best known for their use in the reduction of arenediazonium salts, converting ArN2+ to Ar-H.
 When diazotized in a concentrated solution of Phosphinic acid, an amine substituent can be removed from arenes, selectively over alkyl amines.

Phosphinic acid is prepared by acidifying aqueous solutions of hypophosphite ions, H2PO2−. 
For example, the solution remaining when phosphine is prepared from the reaction of white phosphorus and a base contains the H2PO2− ion. 
If barium hydroxide (BaOH) is used as the base and the solution is acidified with sulfuric acid, barium sulfate, BaSO4, precipitates, and an aqueous solution of Phosphinic acid results.

Ba2+ + 2H2PO2− + 2H3O+ + SO42− → BaSO4 + 2H3PO2 + 2H2OThe pure acid cannot be isolated merely by evaporating the water, however, because of the easy oxidation of the Phosphinic acid to phosphoric acids (and elemental phosphorus) and its disproportionation to phosphine and phosphorous acid. 
The pure acid can be obtained by extraction of its aqueous solution by diethyl ether, (C2H5)2O. Pure Phosphinic acid forms white crystals that melt at 26.5 °C (79.7 °F). 

The electronic structure of Phosphinic acid is such that it has only one hydrogen atom bound to oxygen, and it is thus a monoprotic oxyacid. 
It is a weak acid and forms only one series of salts, the hypophosphites. 
Hydrated sodium hypophosphite, NaH2PO2 · H2O, is used as an industrial reducing agent, particularly for the electroless plating of nickel onto metals and nonmetals

Phosphinic acid is used as a pharmaceutical additive as antioxidant, as an ingredient of electroless plating solutions, for the retrieval of precious or non-ferrous metals as a water treatment agent, as a meat preservative to prevent the discoloration of polymers and for the production of chemicals

Phosphinic acid is also known as "hypophosphite" It is colorless oil or deliquescence crystal , it is an important fine chemical product. The main use is as reducing agent for electroless plating, phosphoric prevent discoloration of resins, it can also be used in the esterification reaction catalyst, the refrigerant, in particular for the production of high purity product sodium hypophosphite. There are several methods for preparation, the common industrial method for producing is ion exchange resin method and electrodialysis method.
The chemical properties of Phosphinic acid, uses, toxicity, and production methods are edited by andy of Chemicalbook. (2016-12-04)

Chemical properties
It is deliquescent crystals or colorless oil. Melting point: 26.5℃. The relative density (specific gravity): 1.439 (solid, 19℃). It is soluble in water, ethanol and ether, and it can be mixed in any proportion with water, ethanol, acetone. In the air, it easily deliquesce to syrupy liquid, and the aqueous solution is acidic.

Phosphinic acid is monobasic acid, in aqueous solution, Phosphinic acid is strong acid, Ka = 10-2 (25℃); it is relatively stable at room temperature; disproportionation reaction can proceed at 130℃, decompose into phosphine and phosphorous acid:
2H3PO2=H3PO4+PH3

It has strong reduction, heavy metal salt solution can be restored to metals such as Cu2 +, Hg2 +, Ag +, such as:
4Ag+H3PO2+2H2)=4Ag+H3PO4+4H+
It is weak oxidizer, it can be reduced to phosphine, phosphine when encounters strong reducing agent.

Uses
Phosphinic acid is used as reducing agent for electroless plating;
Phosphinic acid can be used to prevent discoloration of phosphoric acid resin;
Phosphinic acid is used as esterification catalyst, the refrigerant;
Phosphinic acid is used to produce hypophosphite, sodium salts, manganese salts, iron salts are generally used as nourishing substances;
Phosphinic acid is used in medicine and as reducing agent, the determination of arsenic, tellurium and separation of tantalum, niobium and other reagents.

Phosphinic acid is strong reducing agent, It can be used for the preparation of sodium hypophosphite, calcium phosphate and other hypophosphite.
Phosphinic acid can be used for the plating bath. Pharmaceuticals. reducing agent. general reagents.
Phosphinic acid is strong reducing agent, it can be used in making sodium hypophosphite, calcium phosphate and other hypophosphite.
Phosphinic acid is widely used as reducing agent, Ag, Cu, Ni, Hg and other metals are reduced to the corresponding metal, for the verification of As, Nb, Ta and other reagents, it can be used for the preparation of Na, K, Ca, Mn, Fe and other types of hypophosphite.

Toxicity
Phosphinic acid is non-combustible. But when contacts with the hole H agent, it will cause fire. When meets oxidizing agent, violent reaction and combustion can proceed. When it is heated to high, it can decompose into highly toxic phosphine gas, or even explode. It is corrosive. Phosphinic acid is often added into soft drinks, and because it is not absorbed. So the risk is small, but particularly strong hypophosphite hurt gastrointestinal. Accidentally it splashes into the eyes or contacts skin, plenty of water is used to washed. Production operators should wear protective clothing and other protective clothing. Production equipment should be sealed, workshop should be ventilated well.

HAZARDS IDENTIFICATION
Hazard statement:
Causes severe skin burns and eye damage.
Causes serious eye damage
Precautionary statements:
Do not breathe dust/fume/gas/mist/vapors/spray.
Wash thoroughly after handling.

Wear protective gloves and eye/face protection.
IF SWALLOWED: Rinse mouth. Do NOT induce vomiting.
IF ON SKIN (or hair): Remove/Take off immediately all contaminated clothing. Rinse skin with water/shower.
IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if
present and easy to do. Continue rinsing.
IF INHALED: Remove victim to fresh air and keep at rest in a position comfortable for breathing.
Immediately call a POISON CENTRE or doctor/physician.
Store locked up.
Dispose of this material and its container to hazardous or special waste collection point.

Preparation method
Phosphorus and barium hydroxide solution is heated,  barium salt Ba (H2PO2) 2 • 2H2O can generate, sulfuric acid is added into Phosphinic acid barium solution, Ba2+ can precipitate:
Ba(H2PO2)2+H2SO4=BaSO4+2H3PO2
Phosphinic acid can be obtained by evaporating under reduced pressure and low temperature crystallization. Due to in this process, the solubility of the barium salt is small, so the concentration of obtained Phosphinic acid is not high, industrial product should be purified by recrystallization.

The barium oxide (or lime) and solution of white phosphorus is heated together to form secondary barium phosphate (or calcium), and then reacts with sulfuric acid, it is filtered, concentrated to obtain product, or sodium hypophosphite solution proceeds H-type ion exchange resin can derive product. This method requires a large amount of resin, and resin regeneration and washing step is cumbersome, it generally costs more than $ 7 per pound, it is only suitable for small batch production, and not suitable for large-scale industrial applications.

Phosphinic acid is prepared by electrodialysis method, wherein the electrodialysis cell divides into three parts, they are anode chamber, raw material chamber and cathode chamber, the intermediate is separated by anionic membrane and cationic membrane, between two membranes sodium hypophosphite solution is placed (concentration of 100g/L~500g/L), anode chamber is dilute solution of Phosphinic acid 5g/L, anode chamber is dilute sodium hydroxide solution ( 5g /L), between the poles DC (3V~36V) is passed, anode releases oxygen, and generates secondary product of Phosphinic acid; cathode emits hydrogen, and generates secondary product of sodium hydroxide, the reaction time is 3~21h. The reactions of anode chamber and cathode chamber are as follows:

anode chamber:
H2O==H++OH-
2OH-==O2+2H2O+4e
H++H2PO2-==H3PO2
cathode chamber:
H2O==H++OH-
2H++2e==H2
Na++OH-==NaOH
Electrodialysis method of preparation Phosphinic acid is simple and equipment investment is small, it is suitable for mass production.

Starting from the industrial grade sodium hypophosphite, Cl-, SO42-anions which affect the quality indicators of Phosphinic acid are removed by precipitation, heavy metal ions are removed from the solution by forming sulfide, and then using strong acid cation exchange resin to obtain sodium secondary phosphate, high purity grade product can obtain. The process can produce high-grade secondary phosphate, technically is feasible, the process is simple, easy operation, good product quality, it can meet the needs of the electronics industry, defense industry and other high-tech fields.
Production Process of Phosphinic Acid from Industrial Sodium Hypophosphite
figure 1 Production Process of Phosphinic Acid from Industrial Sodium Hypophosphite.

Ion exchange resin method: about 70g of cation exchange resin wetted with water is packed into a glass tube with 5 mol/L hydrochloric acid circulating about 15min, after thoroughly washed with water, high purity aqueous sodium hypophosphite aqueous solution (15 g/60 ml H2O) flows through it, the resin column is first washed with 50 ml, then with 25 rnl distilled water. The effluent acid and washing is combined, it is concentrated by evaporation in water bath. The concentrated acid is placed in high vacuum with P205 dryer for dehydration, cooling and crystallization, filtration, recrystallization, to obtain Phosphinic acid product.

Production method
Ion exchange resin method: put about 70 g water-soluble cation exchange resins to fill into a glass tube. Circulate with 5 mol/L hydrochloric acid for about 15 min and wash sufficiently with water. Have a high aqueous sodium hypophosphite solution (15 g/60 ml H2O) to flow through the resin column, followed by being washed first with 50 ml water, and then rinsing with 25 rnl distilled water. The effluent acid and the washings were combined and concentrated by evaporation on a water bath. The concentrated acid is send to the highly vacuum, P205 dryer for dehydration, followed by cooling crystallization, filtration and recrystallization to obtain the finished product of Phosphinic acid.

Description
Phosphinic acid is a powerful reducing agent with a molecular formula of H3PO2. Inorganic chemists refer to the free acid by this name although its IUPAC name is dihydridohydroxidooxidophosphorus, or the acceptable name of phosphinic acid. It is a colorless low-melting compound, which is soluble in water, dioxane, and alcohols. The formula for Phosphinic acid is generally written H3PO2, but a more descriptive presentation is HOP(O)H2 which highlights its monoprotic character. Salts derived from this acid are called phosphinates (hypophosphites).

Description
This acid has the general formula ofH4P2O6 and differs from the other oxy-phosphorous acids. It has many peculiarities. It is formed along with phosphorous and phosphoric acids, when phosphorus is oxidized by moist air. If white phosphorus is exposed to air, and sodium acetate is addedto the liquidwhich forms, the somewhat insoluble sodium hypophosphate,Na2H2P2O6·6H2Oseparates. The sodium hypophosphate monohydrate, however, is very soluble and deliquescent at ～98.7 g/100 ml.

Chemical Properties
colourless liquid

Physical properties
Colorless deliquescent crystals or oily liquid; sour odor; density 1.493 g/cm3;melts at 26.5°C; boils at 130°C; very soluble in water, alcohol and ether; den-sity of a 50% aqueous solution is 1.13 g/mL.

Uses
Preparation of hypophosphites, electroplating baths.