Hypophosphoric acid is also called hypophosphite. H3po2 = 65.99, colorless, odorless oily liquid, or deliquescent crystal, easy to absorb moisture. Its melting point is 26.5 ℃, its density is 1.493, and it is decomposed into phosphoric acid and phosphine when heated to 130 ℃. High temperature sulfuric acid oxidation produces sulfur dioxide and sulfur. It is acidic and dissolved in ether. The relationship between water relative density and concentration is: the concentration is 50%, 30% ~ 32%, and the relative density is 1.274.1.13 and 1.04.
Hypophosphorylation can reduce heavy metal salt solution to metal.
X-ray study confirmed that hypophosphoric acid (h2po-2) is a tetrahedron, and there are two kinds of hydrogen directly connected with phosphorus. The structure is as follows:
Hypophosphoric acid configuration
This molecule has three hydrogen atoms, but only one hydroxyl group, so there is only monobasic acid. Hypophosphoric acid in aqueous solution is medium strong acid, Ka = 10-2 (25 ℃). In the temperature range, it is heated to 130 ℃ for decomposition, and the following disproportionation reactions mainly occur:
Secondary phosphorus deposition reaction.
The products include oxidation products such as Biphosphine and phosphite. Hypophosphoric acid dissolves easily in water and ethanol. The dilute solution at normal temperature does not react with oxygen in the air and decomposes in alkaline medium at 100 ℃:
H2PO-2+OH-→HPO-3+H2。
The product is a strong reducing agent and weak oxidant, which can reduce Cu2 +, Hg2 +, Ag +, such as 4ag + + h3po2 + 2H2O = 4ag ↓ + H3PO4 + 4H +.
The strong reducing agent itself is reduced to phosphine phosphine. Commonly used reagents in pharmaceutical industry include arsenic, zirconium, separation tantalum, niobium, etc. Barium hypophosphite is formed by the reaction of white phosphorus with hot concentrated barium hydroxide. Barium hypophosphite is formed by adding sulfuric acid and Ba2 + precipitation.
(H2PO2)2+H2SO4=BaSO4↓+2H3PO2。
Hypophosphoric acid is obtained by vacuum evaporation and low temperature crystallization.
Preparation method
The barium salt BA (H2PO2) 2.2h2o is obtained by heating barium hydroxide solution, and then extracted with dilute sulfuric acid, concentrated and cooled.
Barium hypophosphite solution is added to the dilute sulfuric acid extract or prepared by reacting with calcium hypophosphite (barium hypophosphite) and equivalent sulfuric acid.
Barium hypophosphite BA (H2PO2) 2 was treated with sulfuric acid When sodium hypophosphite solution is treated with H2O or acid ion exchange resin, colorless hypophosphite solution can be obtained, and flake crystals can be obtained after concentration.
purpose
Hypophosphoric acid is used as arsenic, zirconium, separation of tantalum and niobium, and strong reducing agent is used in pharmaceutical industry. Hypophosphoric acid is a very strong reducing monobasic acid with ionization constant k = 8 × 10-2。 When preparing hypophosphite, commonly used supplements such as sodium salt, manganese salt, iron salt, etc.
apply
Medium phosphoric acid can reduce aromatic diazonium salt Ar-N2 + to Ar-H of aromatic hydrocarbons. Aromatic nitration can carry out nitro reduction and diazotization at the same time. Firstly, an amino group is introduced into the aromatic ring, and then a group is introduced into a certain position in the aromatic ring through the localization of the amino group. Diazo removes amino groups.
Hydrated sodium phosphate can be used as an industrial reducing agent, especially for electroless nickel plating on metal, non-metal and plastic surfaces. The nickel surface is generally amorphous or metal nickel containing about 10% phosphorus. Ni3P can improve the hardness of the coating by heating. In addition to hypophosphite, the plating solution also contains nickel chloride (or nickel sulfate), lactic acid (coordination agent), malate or succinate (accelerated deposition) and lead salt (stabilizer).
Iodine is reduced to hydroiodic acid by hypophosphoric acid, and then the two ephedrines are reduced to methamphetamine by hydroiodic acid. Therefore, the drug enforcement agency of the U.S. Department of justice lists this phosphoric acid / phosphate as a precursor chemical and strictly controls its purchase and use. The precursor chemicals are not included in hypophosphite and hypophosphite in the Chinese mainland classification and catalogues, but ephedrine, ephedrine, ephedrine, ephedrine, ephedrine, etc. are used. These chemicals belong to the first category of precursor chemicals and are strictly controlled.
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