Hypophosphorous+Acid

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. == 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.Preparation and availability == P4 + 3OH− + 3H2O → 3H2PO2− + PH3 The free acid may be prepared by the action of a strong acid on these hypophosphite salts. H2PO2− + H+ → H3PO2 Alternatively, H3PO2 arises by the oxidation of [|phosphine] with [|iodine] in water. PH3 + 2I2 + 2H2O → H3PO2 + 4I− + 4H+ HPA is usually supplied as a 50% aqueous solution.
 * Hypophosphorous acid** is a [|phosphorus] [|oxoacid] and a powerful [|reducing agent] with molecular formula H3PO2. Inorganic chemists refer to the free acid by this name (also as "HPA"), 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).

Uses
Hypophosphorous 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 select metal films from solution on a sensitized surface. In organic chemistry, H3PO2 best known for their use in the reduction of [|arenediazonium salts], converting ArN2+ to Ar-H. [|[3]] [|[4]] When [|diazotized] in a concentrated solution of hypophosphorous acid, an [|amine] substituent can be removed from arenes, selectively over alkyl amines.

DEA List I chemical status
Because hypophosphorous acid can reduce elemental [|iodine] to form [|hydroiodic acid], which is a reagent effective for reducing [|ephedrine] or [|pseudoephedrine] to [|methamphetamine] , [|[5]] the [|United States Drug Enforcement Administration] designated hypophosphorous acid (and its salts) as a [|List I precursor chemical] effective November 16, 2001. [|[6]] Accordingly, handlers of hypophosphorous 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.

Inorganic and organic derivatives
Numerous derivatives are known in which the two [|hydrogen] atoms directly bound to phosphorus are replaced by organic groups. These derivatives are known as **phosphinic acids**, and their salts as **phosphinates**. For example, formaldehyde and H3PO2 react to give (HOCH2)2PO2H. The reaction is akin to the addition of thiols and HCN to aldehydes. Similarly, it adds to [|Michael acceptors], for example with acrylamide it gives H(HO)P(O)CH2CH2C(O)NH2. Few metal complexes have been prepared from H3PO2, one example is Ni(O2PH2)2.