| Phosphite | |
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Phosphite[1] |
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| Identifiers | |
| CAS number | 14901-63-4 |
| PubChem | 107908 |
| ChemSpider | 97035 |
| MeSH | Phosphorite |
| ChEBI | CHEBI:45064 |
| ChEMBL | CHEMBL1235376 |
| Gmelin Reference | 68617 |
| Jmol-3D images | Image 1 Image 2 |
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| Properties | |
| Molecular formula | O3P3- |
| Molar mass | 78.9720 g mol-1 |
| Exact mass | 78.958505378 g mol-1 |
| Related compounds | |
| Other anions | Phosphinite |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
A phosphite is a salt of phosphorous acid. The phosphite ion (PO33−) is a polyatomic ion with a phosphorus central atom where phosphorus has an oxidation state of +3.[2] Its molecular geometry is approximately tetrahedral like ammonia.[3]
Because phosphorous acid exists as an equilibrium tautomeric mixture of P(OH)3 and HP(O)(OH)2, predominantly the latter, there is some confusion in nomenclature. The IUPAC recommends[4] that the trihydroxy form be called phosphorous acid and its salts phosphites, with the dihydroxy form being called phosphonic acid and its salts phosphonates, but despite this, salts of HP(O)(OH)2 are often called phosphites rather than phosphonates.
The term phosphite is also used to mean phosphite ester, an organophosphorus compound with the formula P(OR)3.
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Acid or hydrogen phosphites (which the IUPAC recommends be called acid or hydrogen phosphonates), such as NH4HP(O)2OH, can be prepared from phosphorous acid, HP(O)(OH)2.[2] Hydrogen bonding between anions leads to polymeric anionic structures. [3] Recently some others, RbHPHO3, CsHPHO3, TlHPHO3 have been prepared by reacting phosphorous acid with the metal carbonate. These compounds contain a layer polymeric anion consisting of HPO3 tetrahedra linked by hydrogen bonds. These layers are interleaved by layers of metal cations.[5]
Pyrophosphites (diphosphites) can be produced by gently heating acid phosphites under reduced pressure. They contain the ion, H2P2O52−which can be formulated [HP(O)2O−P(O)2H]2−.[2][3]
The traditional name for HPO32− is phosphite, and for HPO2(OH)− is hydrogenphosphite or acid phosphite. However IUPAC recommendations are that HPO32− is to be named hydrogenphosphite or phosphonate, HPO2(OH)− is to be named dihydrogenphosphite or hydrogenphosphonate and phosphite is reserved for the hypothetical PO33− ion. [4]
Organophosphorus compounds called phosphite esters (or sometimes just phosphites) have the formula (RO)3P. They are prepared by reacting phosphorus trichloride (or phosphorus tribromide) with an alcohol and a tertiary amine.
PCl3 + 3 ROH + 3 R'3N → P(OR)3 + 3R'3NHCl
Inorganic phosphites have been applied to crops to combat fungus-like pathogens of the order Oomycetes. The situation is confusing because of the similarity in name between phosphite and phosphate (a major plant nutrient and fertilizer ingredient), and controversial because phosphites have sometimes been advertised as fertilizers, even though they are converted to phosphate too slowly to serve as a plant's main phosphorus source. Lemoynie[6] and others[7] have described this complicated situation and noted that calling phosphites fertilizers avoided the regulatory complication and negative public perceptions that might have been incurred by registering them as fungicides.