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Hypophosphorous Acid (HPA), or phosphinic acid, is a phosphorus oxyacid and a powerful reducing agent with molecular formula H3PO2.
Hypophosphorous Acid (HPA) is a colorless low-melting compound, which is soluble in water, dioxane and alcohols.
The formula for Hypophosphorous Acid (HPA) is generally written H3PO2, but a more descriptive presentation is HOP(O)H2, which highlights its monoprotic character.
CAS: 6303-21-5
MF: HO2P
MW: 63.980501
EINECS: 228-601-5
Synonyms: HYPOPHOSPHOROUSACID,30%(W/V)SOLUTION;HYPOPHOSPHOROUSACID,50%(W/V)SOLUTION;Hypophosphorus acid: (Phosphinic acid);Hypophosphorus acid, 50% w/w aq. soln.;hypophosphorous;hypophosphorousacid(corrosiveliquid,acidic,inorganic,n.o.s.);Hypophosphorousacid,50%w/waq.soln.;HYPOPHOSPHOROUS ACID SOLUTION 50% AQUEOUS
Salts derived from Hypophosphorous Acid (HPA) are called hypophosphites.
HOP(O)H2 exists in equilibrium with the minor tautomer HP(OH)2.
Sometimes the minor tautomer is called hypophosphorous acid and the major tautomer is called phosphinic acid.
Hypophosphorous Acid (HPA) is also known as "hypophosphite"
Hypophosphorous Acid (HPA) 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, Hypophosphorous Acid (HPA) 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.
Hypophosphorous Acid (HPA) 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.
Hypophosphorous Acid (HPA) is a colorless low-melting compound, which is soluble in water, dioxane, and alcohols.
The formula for Hypophosphorous Acid (HPA) is generally written H3PO2, but a more descriptive presentation is HOP(O)H2 which highlights its monoprotic character.
Salts derived from Hypophosphorous Acid (HPA) are called phosphinates (hypophosphites).
Hypophosphorous Acid (HPA) has the general formula ofH4P2O6 and differs from the other oxy-phosphorous acids.
Hypophosphorous Acid (HPA) has many peculiarities.
Hypophosphorous Acid (HPA) 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.
A white crystalline solid.
Hypophosphorous Acid (HPA) is a monobasic acid forming the anion H2PO2 – in water.
The sodium salt, and hence the acid, can be prepared by heating yellow phosphorus with sodium hydroxide solution.
The free acid and its salts are powerful reducing agents.
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.
Hypophosphorous Acid (HPA) is formed by reaction of barium hypophosphite and sulfuric acid, and filtering off barium sulfate.
By evaporation of the solution in vacuum at 80 °C, and then cooling to 0°C, hypophosphorous acid crystallizes.
Hypophosphorous Acid (HPA) appears as colorless oily liquid or deliquescent crystals with a sour odor.
Density 1.439 g / cm3.
Melting point 26.5°C.
Inhalation of vapors irritates or burns the respiratory tract.
Liquid and vapors may irritate or burn eyes and skin.
Hypophosphorous Acid (HPA), also known as Phosphinic Acid, is an inorganic compound.
Hypophosphorous Acid (HPA) is a colourless, hygroscopic, crystalline solid, which is moderately soluble in water.
Hypophosphorous Acid (HPA) is an organophosphorus compound characterized by the presence of a phosphorus atom bonded to a hydroxyl group (-OH) and a hydrogen atom, making it a simple phosphonic acid.
Hypophosphorous Acid (HPA) typically appears as a colorless to pale yellow liquid and is soluble in water and organic solvents.
Hypophosphorous Acid (HPA) is known for its role as a reducing agent and is utilized in various chemical syntheses and applications, including as a stabilizer in polymer formulations and as a precursor in the production of phosphine derivatives.
Hypophosphorous Acid (HPA) exhibits moderate acidity, with a pKa value indicating its ability to donate protons in solution.
Additionally, Hypophosphorous Acid (HPA) can participate in various chemical reactions, including esterification and amidation, making it versatile in organic synthesis.
Safety considerations include handling Hypophosphorous Acid (HPA) with care, as it may pose health risks upon exposure.
Overall, Hypophosphorous Acid (HPA) is an important compound in both industrial and research settings due to its unique chemical properties.
Hypophosphorous Acid (HPA) Chemical Properties
Melting point: -25 °C
Boiling point: 108 °C (759.8513 mmHg)
Density: 1.206 g/mL at 20 °C(lit.)
Vapor pressure: <17 mmHg ( 20 °C)
Storage temp.: no restrictions.
Solubility: very soluble in H2O, ethanol, ethyl ether
Pka: pK1 1.1.
Form: hygroscopic crystals or colorless oily liquid
Color: Colorless
PH: pKa1= 1.00(25℃)
Water Solubility: SOLUBLE
Merck: 13,4894
Stability: Stable. Incompatible with strong bases. Reacts violently with oxidizing agents, strong bases, mercury (II) nitrate and mercury (II) oxide. Do not heat above 100 C.
InChIKey: GQZXNSPRSGFJLY-UHFFFAOYSA-N
CAS DataBase Reference: 6303-21-5(CAS DataBase Reference)
NIST Chemistry Reference:Hypophosphorous Acid (HPA)(6303-21-5)
EPA Substance Registry System: Hypophosphorous Acid (HPA) (6303-21-5)
Hypophosphorous Acid (HPA) is deliquescent crystals or colorless oil.
Melting point: 26.5℃. The relative density (specific gravity): 1.439 (solid, 19℃).
Hypophosphorous Acid (HPA) is soluble in water, ethanol and ether, and it can be mixed in any proportion with water, ethanol, acetone.
In the air, Hypophosphorous Acid (HPA) easily deliquesce to syrupy liquid, and the aqueous solution is acidic.
Hypophosphorous Acid (HPA) is monobasic acid, in aqueous solution, Hypophosphorous 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
Hypophosphorous Acid (HPA) 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+
Hypophosphorous Acid (HPA) is weak oxidizer, it can be reduced to phosphine, phosphine when encounters strong reducing agent.
The molecule displays P(═O)H to P–OH tautomerism similar to that of phosphorous acid; the P(═O) form is strongly favoured.
Hypophosphorous Acid (HPA) is usually supplied as a 50% aqueous solution and heating at low temperatures (up to about 90 °C) prompts it to react with water to form phosphorous acid and hydrogen gas.
H3PO2 + H2O → H3PO3 + H2
Heating above 110 °C causes hypophosphorous acid to undergo disproportionation to give phosphorous acid and phosphine.
3 H3PO2 → 2 H3PO3 + PH3
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.
Reactions
Hypophosphorous Acid (HPA) is miscible with water in all proportions and a commercial strength is 30% H3PO2.
Hypophosphites are used in medicine.
Hypophosphorous Acid (HPA) is a powerful reducing agent, e.g., with copper sulfate forms cuprous hydride Cu2H2, brown precipitate, which evolves hydrogen gas and leaves copper on warming; with silver nitrate yields finely divided silver; with sulfurous acid yields sulfur and some hydrogen sulfide; with sulfuric acid yields sulfurous acid, which reacts as above; forms manganous immediately with permanganate.
Uses
1. Hypophosphorous Acid (HPA) is used as reducing agent for electroless plating;
2. Hypophosphorous Acid (HPA) can be used to prevent discoloration of phosphoric acid resin;
3. Hypophosphorous Acid (HPA) is used as esterification catalyst, the refrigerant;
4. Hypophosphorous Acid (HPA) is used to produce hypophosphite, sodium salts, manganese salts, iron salts are generally used as nourishing substances;
5. Hypophosphorous Acid (HPA) is used in medicine and as reducing agent, the determination of arsenic, tellurium and separation of tantalum, niobium and other reagents.
6. Hypophosphorous Acid (HPA) is strong reducing agent, It can be used for the preparation of sodium hypophosphite, calcium phosphate and other hypophosphite.
7. Hypophosphorous Acid (HPA) can be used for the plating bath. Pharmaceuticals. reducing agent.
8. Hypophosphorous Acid (HPA) is strong reducing agent, it can be used in making sodium hypophosphite, calcium phosphate and other hypophosphite.
9. Hypophosphorous Acid (HPA) 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.
Hypophosphorous Acid (HPA) is primarily used for electroless nickel plating.
Hypophosphorous Acid (HPA) is involved in the reduction of arenediazonium salts.
Hypophosphorous Acid (HPA) acts as an additive in Fischer esterification reactions.
Also, Hypophosphorous Acid (HPA) serves as a neutralizing agent, antioxidant, catalyst in polymerization and poly condensation, and wetting agent.
Further, Hypophosphorous Acid (HPA) is used in the formulation of pharmaceuticals, discoloration of polymers, water treatment and retrieval of precious or non-ferrous metals.
In addition to this, Hypophosphorous Acid (HPA) is used as bleaching agents for plastics, synthetic fibers, decolorizing agent and for color stabilization during the manufacture of chemicals and several plastics.
Preparation method
1. Phosphorus and barium hydroxide solution is heated, barium salt Ba (H2PO2) 2 • 2H2O can generate, sulfuric acid is added into hypophosphorous acid barium solution, Ba2+ can precipitate:
Ba(H2PO2)2+H2SO4=BaSO4+2H3PO2
Hypophosphorous Acid (HPA) 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 Hypophosphorous acid is not high, industrial product should be purified by recrystallization.
2. 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, Hypophosphorous Acid (HPA) 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.
3. Hypophosphorous Acid (HPA) 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 Hypophosphorous 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 Hypophosphorous Acid (HPA); 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 Hypophosphorous acid is simple and equipment investment is small, Hypophosphorous Acid (HPA) is suitable for mass production.
4. Starting from the industrial grade sodium hypophosphite, Cl-, SO42-anions which affect the quality indicators of Hypophosphorous 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.
Preparation and availability
Hypophosphorous Acid (HPA) was first prepared in 1816 by the French chemist Pierre Louis Dulong (1785–1838).
Hypophosphorous Acid (HPA) is prepared industrially via a two step process: Firstly, elemental white phosphorus reacts with alkali and alkaline earth hydroxides to give an aqueous solution of hypophosphites:
P4 + 4 OH− + 4 H2O → 4 H2PO−2 + 2 H2
Any phosphites produced in this step can be selectively precipitated out by treatment with calcium salts.
The purified material is then treated with a strong, non-oxidizing acid (often sulfuric acid) to give the free hypophosphorous acid:
H2PO−2 + H+ → H3PO2
Hypophosphorous Acid (HPA) is usually supplied as a 50% aqueous solution.
Anhydrous acid cannot be obtained by simple evaporation of the water, as the acid readily oxidises to phosphorous acid and phosphoric acid and also disproportionates to phosphorous acid and phosphine.
Pure anhydrous Hypophosphorous Acid (HPA) can be formed by the continuous extraction of aqueous solutions with diethyl ether.
