hypophosphorous acid CAS 6303-21-5 has the general formula of H4P2O6 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 Name | Hypophosphorous acid 50% |
| Synonyms | hypophosphorous; Hypophosphorous acid solution ; phosphinic acid 50% ; HYPOPHOSPHOROUS ACID 50 %, PURE; Hypophosphorousacidcolorlessliq; |
| CAS Number | 6303-21-5 |
| EINECS | 228-601-5 |
| Appearance | colourless liquid |
| storage temp. | no restrictions. |
| form | hygroscopic crystals or colorless oily liquid |
| 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. |
| Uses | Preparation of hypophosphites, electroplating baths. |
| Air & Water Reactions | Deliquescent. Water soluble. |
| Hazard | Fire and explosion risk in contact with oxidizing agents. |
| Description | Hypophosphorous 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 hypophosphorous 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). |
[hypophosphorous acid 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.
[hypophosphorous acid Definition]
A white crystalline solid. It 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.
[Definition]
ChEBI: 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 Preparation]
Hypophosphorous acid may be prepared by various methods:
1. Boiling white phosphorus with calcium hydroxide:
P4 + 4Ca(OH)2 + 8H2O → 4Ca(H2PO2)2 + 4H2
The calcium salt is soluble in water. Treatment with sulfuric acid yields thehypophosphorous acid:
(H2PO2)2Ca + H2SO4 → 2H3PO2 + CaSO4
The product mixture is filtered to remove insoluble CaSO4. The aqueous solu-tion of hypophosphorous acid is concentrated under reduced pressure.Concentrated baryta water may be used instead of calcium hydroxide.2. By treating sodium hypophosphite, NaH2PO2with an ion-exchange resin.The sodium salt may be produced by boiling white phosphorus with a solutionof sodium hydroxide, a reaction similar to (1) above.
PH3 + 2I2 + 2H2O → H3PO2 + 4HI
The above method may be considered safer than that involving heating whitephosphorus with an alkali.
Hypophosphorous acid must be stored below 50°C. It is sold commerciallyas an aqueous solution at various concentrations.
[Production Methods]
Hypophosphorous acid 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.
[Reactions]
Hypophosphorous acid is miscible with water in all proportions and a commercial strength is 30% H3PO2. Hypophosphites are used in medicine. Hypophosphorous acid 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.
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