Phosphite (ion)

The IUPAC recommended name for phosphorous acid is phosphonic acid. Correspondingly, the IUPAC-recommended name for the ion is phosphonate. 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. In practice any reference to "phosphite" should be investigated to determine the naming convention being employed. ==Salts containing HPO32−, called phosphonates or phosphites==

:. The anion has C3v symmetry. From the commercial perspective, the most important phosphite salt is basic lead phosphite. Many salts containing the phosphite ion have been investigated structurally, these include sodium phosphite pentahydrate (Na2HPO3·5H2O). (NH4)2HPO3·H2O, CuHPO3·H2O, SnHPO3 and Al2(HPO3)3·4H2O. The structure of is approximately tetrahedral. has a number of canonical resonance forms making it isoelectronic with bisulfite 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−. A typical derivative is the salt [NH4][HP(O)2OH]. Organic esters of hydrogen phosphites are anions with the formula HP(O)2OR− (R = organic group). One commercial example is the fungicide fosetyl-Al with the formula [C2H5OP(H)O2]3Al. ==Salts containing H2P2O52−, 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 [HP(O)2O−P(O)2H]2−. An example is potassium diplatinum(II) tetrakispyrophosphite. ==Valence-isoelectronic ions==

In contrast to the paucity of evidence for , the corresponding arsenic ion, ortho-arsenite, is known. An example is Ag3AsO3 as well as the polymeric meta-arsenite . The iso-electronic sulfite ion, is known from its salts. 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--> ==Use as fungicides==

Inorganic phosphites (containing ) have been applied to crops to combat fungus-like pathogens of the order oomycetes (water molds). 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. In fact, phosphites may cause phytotoxicity when a plant is starved of phosphates. 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 not serve as a phosphorus fertilizer, but does serve as a potassium fertilizer. ==See also==