Hypophosphorous acid

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Hypophosphorous acid [1]
Wireframe model of hypophosphorous acid Hypophosphorous-acid-2D.png
Wireframe model of hypophosphorous acid
Hypophosphorous-acid-3D-balls.png
Names
IUPAC name
Phosphinic acid
Other names
Hydroxy(oxo)-λ5-phosphane

Hydroxy-λ5-phosphanone
Oxo-λ5-phosphanol
Oxo-λ5-phosphinous acid

Phosphonous acid (for minor tautomer)

Contents

Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.026.001 OOjs UI icon edit-ltr-progressive.svg
KEGG
PubChem CID
UNII
UN number UN 3264
  • InChI=1S/H3O2P/c1-3-2/h3H2,(H,1,2) Yes check.svgY
    Key: ACVYVLVWPXVTIT-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/H3O2P/c1-3-2/h3H2,(H,1,2)
    Key: ACVYVLVWPXVTIT-UHFFFAOYAQ
  • O[PH2]=O
Properties
H3PO2
Molar mass 66.00 g/mol
Appearancecolorless, deliquescent crystals or oily liquid
Density 1.493 g/cm3 [2]

1.22 g/cm3 (50 wt% aq. solution)

Melting point 26.5 °C (79.7 °F; 299.6 K)
Boiling point 130 °C (266 °F; 403 K) decomposes
miscible
Solubility very soluble in alcohol, ether
Acidity (pKa)1.2
Conjugate base Phosphinate
Structure
pseudo-tetrahedral
Hazards
Flash point Non-flammable
Safety data sheet (SDS) JT Baker
Related compounds
Phosphorous acid
Phosphoric acid
Related compounds
Sodium hypophosphite
Barium hypophosphite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Hypophosphorous acid (HPA), or phosphinic acid, is a phosphorus oxyacid and a powerful reducing agent with molecular formula H3PO2. It is a colorless low-melting compound, which is soluble in water, dioxane and alcohols. The formula for this 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 hypophosphites. [3]

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.

Preparation and availability

Hypophosphorous acid was first prepared in 1816 by the French chemist Pierre Louis Dulong (1785–1838). [4]

The acid 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 H
2
PO
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:

H
2
PO
2
+ H+ → H3PO2

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 can be formed by the continuous extraction of aqueous solutions with diethyl ether. [5]

Properties

Tautomerism of H3PO2.png

The molecule displays P(═O)H to P–OH tautomerism similar to that of phosphorous acid; the P(═O) form is strongly favoured. [6]

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. [7]

3 H3PO2 → 2 H3PO3 + PH3

Reactions

Inorganic

Hypophosphorous acid can reduce chromium(III) oxide to chromium(II) oxide:

H3PO2 + 2 Cr2O3 → 4 CrO + H3PO4

Inorganic derivatives

Most metal-hypophosphite complexes are unstable, owing to the tendency of hypophosphites to reduce metal cations back into the bulk metal. Some examples have been characterised, [8] [9] including the important nickel salt [Ni(H2O)6](H2PO2)2. [10]

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, [11] the United States Drug Enforcement Administration designated hypophosphorous acid (and its salts) as a List I precursor chemical effective November 16, 2001. [12] 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. [12] [13] [14]

Organic

In organic chemistry, H3PO2 can be used for the reduction of arenediazonium salts, converting ArN+
2
to Ar–H. [15] [16] [17] When diazotized in a concentrated solution of hypophosphorous acid, an amine substituent can be removed from arenes.

Owing to its ability to function as a mild reducing agent and oxygen scavenger it is sometimes used as an additive in Fischer esterification reactions, where it prevents the formation of colored impurities.

It is used to prepare phosphinic acid derivatives. [18]

Applications

Hypophosphorous acid (and its salts) are used to reduce metal salts back into bulk metals. It is effective for various transition metals ions (i.e. those of: Co, Cu, Ag, Mn, Pt) but is most commonly used to reduce nickel. [19] This forms the basis of electroless nickel plating (Ni–P), which is the single largest industrial application of hypophosphites. For this application it is principally used as a salt (sodium hypophosphite). [20]

Sources

Related Research Articles

<span class="mw-page-title-main">Phosphate</span> Anion, salt, functional group or ester derived from a phosphoric acid

In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid, a.k.a. phosphoric acid H3PO4.

<span class="mw-page-title-main">Hydrogenation</span> Chemical reaction between molecular hydrogen and another compound or element

Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically constitutes the addition of pairs of hydrogen atoms to a molecule, often an alkene. Catalysts are required for the reaction to be usable; non-catalytic hydrogenation takes place only at very high temperatures. Hydrogenation reduces double and triple bonds in hydrocarbons.

<span class="mw-page-title-main">Phosphine</span> Chemical compound hydrogen phosphide

Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula PH3, classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting fish, due to the presence of substituted phosphine and diphosphane (P2H4). With traces of P2H4 present, PH3 is spontaneously flammable in air (pyrophoric), burning with a luminous flame. Phosphine is a highly toxic respiratory poison, and is immediately dangerous to life or health at 50 ppm. Phosphine has a trigonal pyramidal structure.

<span class="mw-page-title-main">Phosphite anion</span> Ion

A phosphite anion or phosphite in inorganic chemistry usually refers to [HPO3]2− but includes [H2PO3] ([HPO2(OH)]). These anions are the conjugate bases of phosphorous acid (H3PO3). The corresponding salts, e.g. sodium phosphite (Na2HPO3) are reducing in character.

<span class="mw-page-title-main">Hydrazoic acid</span> Unstable and toxic chemical compound

Hydrazoic acid, also known as hydrogen azide, azic acid or azoimide, is a compound with the chemical formula HN3. It is a colorless, volatile, and explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, and is therefore a pnictogen hydride. The oxidation state of the nitrogen atoms in hydrazoic acid is fractional and is -1/3. It was first isolated in 1890 by Theodor Curtius. The acid has few applications, but its conjugate base, the azide ion, is useful in specialized processes.

<span class="mw-page-title-main">Triphenylphosphine</span> Chemical compound

Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to PPh3 or Ph3P. It is versatile compound that is widely used as a reagent in organic synthesis and as a ligand for transition metal complexes, including ones that serve as catalysts in organometallic chemistry. PPh3 exists as relatively air stable, colorless crystals at room temperature. It dissolves in non-polar organic solvents such as benzene and diethyl ether.

<span class="mw-page-title-main">Phosphorus triiodide</span> Chemical compound

Phosphorus triiodide (PI3) is an inorganic compound with the formula PI3. A red solid, it is too unstable to be stored for long periods of time; it is, nevertheless, commercially available. It is widely used in organic chemistry for converting alcohols to alkyl iodides. It is also a powerful reducing agent.

<span class="mw-page-title-main">Phosphorous acid</span> Chemical compound (H3PO3)

Phosphorous acid is the compound described by the formula H3PO3. This acid is diprotic, not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in the preparation of other phosphorus compounds. Organic derivatives of phosphorous acid, compounds with the formula RPO3H2, are called phosphonic acids.

Borderline hydrides typically refer to hydrides formed of hydrogen and elements of the periodic table in group 11 and group 12 and indium (In) and thallium (Tl). These compounds have properties intermediate between covalent hydrides and saline hydrides. Hydrides are chemical compounds that contain a metal and hydrogen acting as a negative ion.

In chemistry, phosphorus oxoacid is a generic name for any acid whose molecule consists of atoms of phosphorus, oxygen, and hydrogen. There is a potentially infinite number of such compounds. Some of them are unstable and have not been isolated, but the derived anions and organic groups are present in stable salts and esters. The most important ones—in biology, geology, industry, and chemical research—are the phosphoric acids, whose esters and salts are the phosphates.

Phosphinates or hypophosphites are a class of phosphorus compounds conceptually based on the structure of hypophosphorous acid. IUPAC prefers the term phosphinate in all cases, however in practice hypophosphite is usually used to describe inorganic species, while phosphinate typically refers to organophosphorus species.

<span class="mw-page-title-main">Electroless deposition</span>

Electroless deposition (ED) or electroless plating is defined as the autocatalytic process through which metals and metal alloys are deposited onto conductive and nonconductive surfaces. These nonconductive surfaces include plastics, ceramics, and glass etc., which can then become decorative, anti-corrosive, and conductive depending on their final functions. Electroplating, unlike electroless deposition, only deposits on other conductive or semi-conductive materials when an external current is applied. Electroless deposition deposits metals onto 2D and 3D structures such as screws, nanofibers, and carbon nanotubes, unlike other plating methods such as Physical Vapor Deposition ( PVD), Chemical Vapor Deposition (CVD), and electroplating, which are limited to 2D surfaces. Commonly the surface of the substrate is characterized via pXRD, SEM-EDS, and XPS which relay set parameters based their final funtionality. These parameters are referred to a Key Performance Indicators crucial for a researcher’ or company's purpose. Electroless deposition continues to rise in importance within the microelectronic industry, oil and gas, and aerospace industry.

<span class="mw-page-title-main">Phosphite ester</span> Organic compound with the formula P(OR)3

In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of an unobserved tautomer phosphorous acid, H3PO3, with the simplest example being trimethylphosphite, P(OCH3)3. Some phosphites can be considered esters of the dominant tautomer of phosphorous acid (HP(O)(OH)2). The simplest representative is dimethylphosphite with the formula HP(O)(OCH3)2. Both classes of phosphites are usually colorless liquids.

Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective insecticides, although some are extremely toxic to humans, including sarin and VX nerve agents.

<span class="mw-page-title-main">Electroless nickel-phosphorus plating</span> Chemical-induced nickel coating of a surface

Electroless nickel-phosphorus plating, also referred to as E-nickel, is a chemical process that deposits an even layer of nickel-phosphorus alloy on the surface of a solid substrate, like metal or plastic. The process involves dipping the substrate in a water solution containing nickel salt and a phosphorus-containing reducing agent, usually a hypophosphite salt. It is the most common version of electroless nickel plating and is often referred by that name. A similar process uses a borohydride reducing agent, yielding a nickel-boron coating instead.

<span class="mw-page-title-main">Phosphine oxides</span> Class of chemical compounds

Phosphine oxides are phosphorus compounds with the formula OPX3. When X = alkyl or aryl, these are organophosphine oxides. Triphenylphosphine oxide is an example. An inorganic phosphine oxide is phosphoryl chloride (POCl3). The parent phosphine oxide (H3PO) remains rare and obscure.

<span class="mw-page-title-main">Sodium hypophosphite</span> Chemical compound

Sodium hypophosphite (NaPO2H2, also known as sodium phosphinate) is the sodium salt of hypophosphorous acid and is often encountered as the monohydrate, NaPO2H2·H2O. It is a solid at room temperature, appearing as odorless white crystals. It is soluble in water, and easily absorbs moisture from the air.

<span class="mw-page-title-main">Copper hydride</span> Chemical compound

Copper hydride is an inorganic compound with the chemical formula CuHn where n ~ 0.95. It is a red solid, rarely isolated as a pure composition, that decomposes to the elements. Copper hydride is mainly produced as a reducing agent in organic synthesis and as a precursor to various catalysts.

<span class="mw-page-title-main">Diethylphosphite</span> Chemical compound

Diethyl phosphite is the organophosphorus compound with the formula (C2H5O)2P(O)H. It is a popular reagent for generating other organophosphorus compounds, exploiting the high reactivity of the P-H bond. Diethyl phosphite is a colorless liquid. The molecule is tetrahedral.

<span class="mw-page-title-main">Organophosphinic acid</span>

An organophosphinic acid is an organophosphorus compound with the formula R2−nHnPO2H (R = alkyl, aryl). One or both P-H bonds in the parent hypophosphorous acid (aka phosphinic acid) are replaced by organic groups. The Cyanex family of dialkylphosphinic acids are used in hydrometallurgy to extract metals from ores.

References

  1. Petrucci, Ralph H. (2007). General Chemistry (9th ed.). p. 946.
  2. Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN   0-07-049439-8
  3. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  4. Dulong prepared acide hypo-phosphoreux by adding barium phosphide (Ba3P2) to water, which yielded phosphine gas (PH3), barium phosphate, and barium hypophosphite. Since the phosphine gas left the solution and the barium phosphate precipitated, only the barium hypophosphite remained in solution. Hypophosphorous acid could then be obtained from the filtrate by adding sulfuric acid, which precipitated barium sulfate, leaving hypophosphorous acid in solution. See:
  5. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 513. ISBN   978-0-08-037941-8.
  6. Janesko, Benjamin G.; Fisher, Henry C.; Bridle, Mark J.; Montchamp, Jean-Luc (2015-09-29). "P(═O)H to P–OH Tautomerism: A Theoretical and Experimental Study". The Journal of Organic Chemistry. 80 (20). American Chemical Society (ACS): 10025–10032. doi:10.1021/acs.joc.5b01618. ISSN   0022-3263.
  7. Shechkov, G. T.; Pevneva, I. A.; Meshkova, O. A. (August 2003). "Thermal Disproportionation of Hypophosphorous Acid". Russian Journal of Applied Chemistry. 76 (8): 1354–1355. doi:10.1023/B:RJAC.0000008318.22178.07. S2CID   96861842.
  8. Kuratieva, Natalia V.; Naumova, Marina I.; Podberezskaya, Nina V.; Naumov, Dmitry Yu. (2005-02-15). "The bivalent metal hypophosphites Sr(H 2 PO 2 ) 2 , Pb(H 2 PO 2 ) 2 and Ba(H 2 PO 2 ) 2". Acta Crystallographica Section C Crystal Structure Communications. 61 (2): i14–i16. doi:10.1107/S010827010403166X. PMID   15695880.
  9. Naumova, Marina I.; Kuratieva, Natalia V.; Podberezskaya, Nina V.; Naumov, Dmitry Yu. (2004-05-15). "The alkali hypophosphites KH 2 PO 2 , RbH 2 PO 2 and CsH 2 PO 2". Acta Crystallographica Section C Crystal Structure Communications. 60 (5): i53–i55. doi:10.1107/S0108270104002409. PMID   15131359.
  10. Kuratieva, Natalia V.; Naumova, Marina I.; Naumov, Dmitry Yu.; Podberezskaya, Nina V. (2003-01-15). "Hexaaquanickel(II) bis(hypophosphite)". Acta Crystallographica Section C Crystal Structure Communications. 59 (1): i1–i3. doi:10.1107/S0108270102018541. PMID   12506208.
  11. Gordon, P. E.; Fry, A. J.; Hicks, L. D. (23 August 2005). "Further studies on the reduction of benzylic alcohols by hypophosphorous acid/iodine" (PDF). Arkivoc. 2005 (vi): 393–400. ISSN   1424-6376.
  12. 1 2 66 FR 52670—52675. 17 October 2001.
  13. "21 CFR 1309". Archived from the original on 2009-05-03. Retrieved 2007-05-02.
  14. 21 USC, Chapter 13 (Controlled Substances Act)
  15. William H. Brown; Brent L. Iverson; Eric Anslyn; Christopher S. Foote (2013). Organic Chemistry. Cengage Learning. p. 1003. ISBN   978-1-133-95284-8.
  16. Robison, M. M.; Robison, B. L. "2,4,6-Tribromobenzoic acid". Organic Syntheses . 36: 94; Collected Volumes, vol. 4.
  17. Kornblum, N. (1941). "3,3′-Dimethoxybiphenyl and 3,3′-Dimethylbiphenyl". Organic Syntheses . 21: 30. doi:10.15227/orgsyn.021.0030 .
  18. Karla Bravo-Altamirano; Jean-Luc Montchamp (2008). "Palladium-Catalyzed Dehydrative Allylation of Hypophosphorous Acid with Allylic Alcohols". Org. Synth. 85: 96. doi: 10.15227/orgsyn.085.0096 .
  19. Guyon, Carole; Métay, Estelle; Popowycz, Florence; Lemaire, Marc (2015). "Synthetic applications of hypophosphite derivatives in reduction". Organic & Biomolecular Chemistry. 13 (29): 7879–7906. doi:10.1039/C5OB01032B. PMID   26083977.
  20. Abrantes, L. M. (1994). "On the Mechanism of Electroless Ni–P Plating". Journal of the Electrochemical Society. 141 (9): 2356–2360. Bibcode:1994JElS..141.2356A. doi:10.1149/1.2055125.