 | |||
| |||
| Names | |||
|---|---|---|---|
| IUPAC name Phosphonate | |||
| Systematic IUPAC name Phosphite[1] | |||
| Identifiers | |||
3D model (JSmol) |
| ||
| ChEBI | |||
| ChemSpider |
| ||
| 1618 | |||
| MeSH | Phosphorite | ||
| |||
| |||
| Properties | |||
| HPO2− 3 | |||
| Molar mass | 79.9810 g mol−1 | ||
| Related compounds | |||
Otheranions | Phosphinite | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Aphosphite ion in inorganic chemistry usually refers to [HPO3]2− but includes [H2PO3]− ([HPO2(OH)]−). These anions are the conjugate bases ofphosphorous acid (H3PO3). The corresponding salts, e.g.sodium phosphite (Na2HPO3) are reducing in character.
The IUPAC recommended name for phosphorous acid isphosphonic acid. Correspondingly, the IUPAC-recommended name for theHPO2−
3 ion isphosphonate. In the US the IUPAC naming conventions for inorganic compounds are taught at high school, but not as a 'required' part of the curriculum.[2] A well-known university-level textbook follows the IUPAC recommendations.[3] In practice any reference to "phosphite" should be investigated to determine the naming convention being employed.
From the commercial perspective, the most important phosphite salt isbasic lead phosphite. Many salts containing the phosphite ion have been investigated structurally, these includesodium phosphite pentahydrate (Na2HPO3·5H2O). (NH4)2HPO3·H2O, CuHPO3·H2O, SnHPO3 and Al2(HPO3)3·4H2O.[4] The structure ofHPO2−
3 is approximately tetrahedral.[5][6]
HPO2−
3 has a number of canonical resonance forms making it isoelectronic withbisulfite ion,HSO−
3, which has a similar structure.[7]
Acid or hydrogen phosphites are called hydrogenphosphonates or acid phosphites. IUPAC recommends the name hydrogenphosphonates). They are anions HP(O)2OH−. A typical derivative is the salt [NH4][HP(O)2OH].[7][6] Many related salts are known, e.g., RbHPHO3, CsHPHO3, TlHPHO3. These salts are prepared by treatingphosphorous acid with the metalcarbonate. These compounds contain a layer polymeric anion consisting of HPO3 tetrahedra linked by hydrogen bonds. These layers are interleaved by layers of metal cations.[8]
Organic esters of hydrogen phosphites are anions with the formula HP(O)2OR− (R = organic group). One commercial example is thefungicidefosetyl-Al with the formula [C2H5OP(H)O2]3Al.[9]
Pyrophosphites (diphosphites) can be produced by gently heating acid phosphites under reduced pressure. They contain the ionH
2P
2O2−
5, which can be formulated [HP(O)2O−P(O)2H]2−.[7][6]
In contrast to the paucity of evidence forPO3−
3, the corresponding arsenic ion, ortho-arsenite,AsO3−
3 is known. An example is Ag3AsO3 as well as the polymeric meta-arsenite(AsO−
2)
n.[7] The iso-electronicsulfite ion,SO2−
3 is known from its salts.[7]
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Inorganic phosphites (containingHPO2−
3) have been applied to crops to combat fungus-like pathogens of the orderoomycetes (water molds). The situation is confusing because of the similarity in name between phosphite andphosphate (a major plantnutrient andfertilizer 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. In fact, phosphites may cause phytotoxicity when a plant is starved of phosphates.[10] Lemoynie[11] and others 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.[10]
A major form of inorganic phosphite used in agriculture ismonopotassium phosphite. This compound does serve as a potassium fertilizer.
