A phosphite anion or phosphite in inorganic chemistry usually refers to
3">PO3sup>2− but includes
2PO3">2PO3sup>− (
2(OH)">PO2(OH)sup>−). These anions are the conjugate bases of
phosphorous acid
Phosphorous acid (or phosphonic acid (singular)) is the compound described by the formula H3PO3. This acid is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in th ...
(H
3PO
3). The corresponding salts, e.g.
sodium phosphite
Disodium hydrogen phosphite is the name for inorganic compounds with the formula Na2HPO3.(H2O)x. The commonly encountered salt is the pentahydrate. A derivative of phosphorous acid (HP(O)(OH)2), it contains the anion HPO32−. Its common name su ...
(Na
2HPO
3) are reducing in character.
Nomenclature
The IUPAC recommended name for phosphorous acid is
phosphonic acid. Correspondingly, the IUPAC-recommended name for the ion is
phosphonate
In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing groups (where R = alkyl, aryl, or just hydrogen). Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly ...
. In the US the IUPAC naming conventions for inorganic compounds are taught at high school, but not as a 'required' part of the curriculum. A well-known university-level textbook follows the IUPAC recommendations.
[Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier ] In practice any reference to "phosphite" should be investigated to determine the naming convention being employed.
Salts containing , called phosphonates or phosphites
:
![Disodium hydrogen phosphite](https://upload.wikimedia.org/wikipedia/commons/4/42/Disodium_hydrogen_phosphite.png)
From the commercial perspective, the most important phosphite salt is
basic lead phosphite
Basic lead phosphite is an inorganic compound with the proposed composition Pb3O(OH)2(HPO3). The compound contains the phosphite anion
A phosphite anion or phosphite in inorganic chemistry usually refers to PO3sup>2− but includes 2PO3sup>â ...
. Many salts containing the phosphite ion have been investigated structurally, these include
sodium phosphite
Disodium hydrogen phosphite is the name for inorganic compounds with the formula Na2HPO3.(H2O)x. The commonly encountered salt is the pentahydrate. A derivative of phosphorous acid (HP(O)(OH)2), it contains the anion HPO32−. Its common name su ...
pentahydrate (Na
2HPO
3·5H
2O). (NH
4)
2HPO
3·H
2O, CuHPO
3·H
2O, SnHPO
3 and Al
2(HPO
3)
3·4H
2O. The structure of is approximately tetrahedral.
[L. E. Gordon, W. T. A. Harrison. "Bis(melaminium) hydrogen phosphite tetrahydrate". ''Acta Crystallogr.'' 59 (2): o195–o197. ]["Crystal chemistry of inorganic phosphites", J. Loub, ''Acta Crystallogr.'' (1991), B47, 468–473, ]
has a number of canonical resonance forms making it isoelectronic with
bisulfite
The bisulfite ion (IUPAC-recommended nomenclature: hydrogensulfite) is the ion . Salts containing the ion are also known as "sulfite lyes". Sodium bisulfite is used interchangeably with sodium metabisulfite (Na2S2O5). Sodium metabisulfite disso ...
ion, , which has a similar structure.
Salts containing HP(O)2OH−
Acid or hydrogen phosphites are called hydrogenphosphonates or acid phosphites. IUPAC recommends the name hydrogenphosphonates). They are anions HP(O)
2OH
−. Aypical derivative is the salt
4">H4HP(O)
2OH].
Many related salts are known, e.g., RbHPHO
3, CsHPHO
3, TlHPHO
3. These salts are prepared by treating
phosphorous acid
Phosphorous acid (or phosphonic acid (singular)) is the compound described by the formula H3PO3. This acid is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in th ...
with the metal
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
. These compounds contain a layer polymeric anion consisting of HPO
3 tetrahedra linked by hydrogen bonds. These layers are interleaved by layers of metal cations.
Organic esters of hydrogen phosphites are anions with the formula HP(O)
2OR
− (R = organic group). One commercial example is the
fungicide
Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...
fosetyl-Al with the formula
2H5OP(H)O2">2H5OP(H)O2sub>3Al.
Salts containing , called diphosphites or pyrophosphites
Pyrophosphites (diphosphites) can be produced by gently heating acid phosphites under reduced pressure. They contain the ion , which can be formulated
2O−P(O)2H">P(O)2O−P(O)2Hsup>2−.
Parallels in arsenic chemistry
In contrast to the paucity of evidence for , the corresponding arsenic ion, ortho-
arsenite
In chemistry, an arsenite is a chemical compound containing an arsenic oxyanion where arsenic has oxidation state +3. Note that in fields that commonly deal with groundwater chemistry, arsenite is used generically to identify soluble AsIII anions. ...
, is known. An example is Ag
3AsO
3 as well as the polymeric meta-arsenite .
The iso-electronic
sulfite ion, is known from its salts.
Use as fungicides
Inorganic phosphites (containing ) have been applied to crops to combat fungus-like pathogens of the order
oomycete
Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the resul ...
s (water molds). The situation is confusing because of the similarity in name between phosphite and
phosphate
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 .
The phosphate or orthophosphate ion is derived from phospho ...
(a major plant
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
and
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
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.
[ Lemoynie"Phosphites and Phosphates: When Distributors and Growers alike could get confused!" by Jean-Pierre Leymonie. Courtesy of ''New Ag International'', September 2007 edition.]
/ref> 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.
A major form of inorganic phosphite used in agriculture is monopotassium phosphite. This compound does serve as a potassium fertilizer.
See also
* Hypophosphite
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 ...
–
* Organophosphorus
Organophosphorus compounds 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 in ...
* Phosphine
Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...
– PH3 and the organic phosphines PR3
* Phosphine oxide – OPR3
* Phosphinite
In organic chemistry, phosphinites are organophosphorus compounds with the formula . They are used as ligands in homogeneous catalysis and coordination chemistry.
Preparation
Phosphinites are prepared by alcoholysis of organophosphinous chlor ...
– P(OR)R2
* Phosphonite
In organic chemistry, phosphonites are organophosphorus compounds with the formula P(OR)2R. They are found in some pesticides and are used as ligands.
Preparation
Although they are derivatives of phosphonous acid (RP(OH)2), they are not prepar ...
– P(OR)2R
* Phosphinate
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 inorgani ...
– OP(OR)R2
* Phosphonate
In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing groups (where R = alkyl, aryl, or just hydrogen). Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly ...
– organic phosphonates OP(OR)2R
* Phosphate
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 .
The phosphate or orthophosphate ion is derived from phospho ...
–
* Organophosphate
In organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered a ...
– OP(OR)3
Further reading
*
References
{{reflist
*
Phosphorus oxyanions
Functional groups
Phosphorus(III) compounds