Hypophosphorous acid
2614426
200278588
2008-03-23T11:28:09Z
Axiosaurus
3399137
added IUPAC name
{{Chembox new
| ImageFile = Hypophosphorous-acid-2D.png
| ImageSize = 150px
| ImageName = Hypophosphorous acid
| ImageFile1 = Hypophosphorous-acid-3D-balls.png
| ImageSize1 = 150px
| ImageName1 = Hypophosphorous acid
| IUPACName = Phosphinic acid<br />dihydridohydroxidooxidophosphorus
| Section1 = {{Chembox Identifiers
| CASOther =<!--{{CASREF|CAS=-->6303-21-5
}}
| Section2 = {{Chembox Properties
| Formula = H<sub>3</sub>PO<sub>2</sub>
| MolarMass = 66.00 g/mol
| Density = 1.274 g/cm<sup>3</sup>, liquid
| Solubility = miscible
| MeltingPt = 26.5 °C (299.5 K)
| BoilingPt = 106 °C (379 K) ''decomp.''
| pKa = 1.2
| Viscosity =
}}
| Section3 = {{Chembox Structure
| MolShape = pseudo-tetrahedral
| Dipole =
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://www.jtbaker.com/msds/englishhtml/h8468.htm JT Baker]
| EUClass = not listed
}}
| Section8 = {{Chembox Related
| Function = [[oxoacid]]s
| OtherFunctn = [[Phosphorous acid]]<br />[[Phosphoric acid]]
| OtherCpds = [[Sodium hypophosphite]]<br />[[Barium hypophosphite]]
}}
}}
'''Hypophosphorous acid''' is a [[phosphorus]] [[oxoacid]] and a powerful [[Reduction (chemistry)|reducing agent]] with molecular formula H<sub>3</sub>PO<sub>2</sub>. Inorganic chemists refer to the free acid by this name (also as "HPA") although its [[IUPAC nomenclature of inorganic chemistry|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 H<sub>3</sub>PO<sub>2</sub>, but a more descriptive presentation is HOP(O)H<sub>2</sub> which highlights its [[monoprotic]] character. Salts derived from this acid are called '''hypophosphites'''.
HOP(O)H<sub>2</sub> exists in [[chemical equilibrium|equilibrium]] with the minor [[tautomer]] HP(OH)<sub>2</sub>. Sometimes the minor tautomer is called hypophosphorous 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 metal|alkali]] and [[alkaline earth metal]]s result from treatment of [[Phosphorus|white phosphorus]] with hot aqueous solution of the appropriate [[hydroxide]], e.g. Ca(OH)<sub>2</sub>.
:P<sub>4</sub> + 4OH<sup>−</sup> + 4H<sub>2</sub>O → 4H<sub>2</sub>PO<sub>2</sub><sup>−</sup> + 2H<sub>2</sub>
The free acid may be prepared by the action of a strong acid on these hypophosphite salts.
:H<sub>2</sub>PO<sub>2</sub><sup>−</sup> + H<sup>+</sup> → H<sub>3</sub>PO<sub>2</sub>
Alternatively, H<sub>3</sub>PO<sub>2</sub> arises by the oxidation of [[phosphine]] with [[iodine]] in water.
:PH<sub>3</sub> + 2I<sub>2</sub> + 2H<sub>2</sub>O → H<sub>3</sub>PO<sub>2</sub> + 4I<sup>−</sup> + 4H<sup>+</sup>
HPA is usually supplied as a 50% aqueous solution.
==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 metal films from solution. In organic chemistry, H<sub>3</sub>PO<sub>2</sub> best known for their use in the reduction of [[Diazonium salt|arenediazonium salts]], converting ArN<sub>2</sub><sup>+</sup> to Ar-H.<ref name="robison">Robison, M. M.; Robison, B. L. (1956). "[http://orgsyn.org/orgsyn/prep.asp?prep=cv4p0947 2,4,6-Tribromobenzoic acid]". ''[[Org. Synth.]]'' '''36''':94; ''Coll. Vol.'' '''4''':947.</ref><ref name="kornblum">Kornblum, N. (1941). "[http://orgsyn.org/orgsyn/prep.asp?prep=cv3p0295 3,3'-Dimethoxybiphenyl and 3,3'-dimethylbiphenyl]". ''[[Org. Synth.]]'' '''21''':30; ''Coll. Vol.'' '''3''':295.</ref> When [[diazotization|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]],<ref name="ARKIVOC">Gordon, P.E.; Fry, A.J.; Hicks, L.D. ''Further studies on the reduction of benzylic alcohols by hypophosphorous acid/iodine.'' 23 August 2005. [http://content.arkat-usa.org/ARKIVOC/JOURNAL_CONTENT/manuscripts/2005/EJ-1559CP%20as%20published%20mainmanuscript.pdf ARKIVOC 2005 (vi) 393-400]. [[ISSN|ISSN 1424-6376]].</ref> the [[Drug Enforcement Administration|United States Drug Enforcement Administration]] designated hypophosphorous acid (and its salts) as a [[DEA list of chemicals|List I precursor chemical]] effective November 16, 2001.<ref name="66 CFR 52670">[http://frwebgate.access.gpo.gov/cgi-bin/getdoc.cgi?dbname=2001_register&docid=01-26013-filed 66 FR 52670—52675.] 17 October 2001.</ref> Accordingly, handlers of hypophosphorous acid or its salts in the [[United States of America|United States]] are subject to stringent regulatory controls including registration, recordkeeping, reporting, and import/export requirements pursuant to the [[Controlled Substances Act]] and 21 [[Code of Federal Regulations|CFR]] §§ 1309 and 1310.<ref name="66 CFR 52670"/><ref name="21 CFR 1309">[http://www.access.gpo.gov/nara/cfr/waisidx_06/21cfr1309_06.html 21 CFR 1309]</ref><ref name="CSA">[http://www.usdoj.gov/dea/pubs/csa.html 21 USC, Chapter 13 (Controlled Substances Act)]</ref>
==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 H<sub>3</sub>PO<sub>2</sub> react to give (HOCH<sub>2</sub>)<sub>2</sub>PO<sub>2</sub>H. 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)CH<sub>2</sub>CH<sub>2</sub>C(O)NH<sub>2</sub>.
Few metal complexes have been prepared from H<sub>3</sub>PO<sub>2</sub>, one example is Ni(O<sub>2</sub>PH<sub>2</sub>)<sub>2</sub>.
==Sources==
*{{Cotton&Wilkinson6th}}
* [http://www.chemicalland21.com/arokorhi/industrialchem/inorganic/HYPOPHOSPHOROUS%20ACID.htm ChemicalLand21 Listing]
*D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam. ISBN 0-444-89307-5.
*V. V. Popik, A. G. Wright, T. A. Khan, J. A. Murphy "Hypophosphorous Acid" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.
==References==
<references/>
[[Category:Phosphorus compounds]]
[[Category:Acids]]
[[Category:Reagents for organic chemistry]]
[[Category:DEA List I chemicals]]
[[da:Phosphorundersyrling]]
[[de:Phosphinsäure]]
[[fr:Acide hypophosphoreux]]
[[it:Acido ipofosforoso]]
[[pt:Ácido hipofosforoso]]
[[ru:Фосфорноватистая кислота]]