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In chemistry, an arsenite is a chemical compound containing an arsenic oxoanion 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. IUPAC have recommended that arsenite compounds are to be named as arsenate(III), for example ortho-arsenatite is called trioxidoarsenate(III). Ortho-arsenite contrasts to the corresponding anions of the lighter members of group 15, phosphite which has the structure HPO2−
3 and nitrite, NO−
2 which is bent.
Contents
- Arsenite ion aso3 3 lewis dot structure
- Preparation of arsenites
- Arsenite minerals
- Arsenites in the environment
- Uses
- Bacteria using and generating arsenite
- References
A number of different arsenite anions are known:
3 ortho-arsenite, an ion of arsenous acid, with a pyramidal shape
2]
n meta-arsenite, a polymeric chain anion.
2O4−
5 pyro-arsenite, O2As–O–AsO2
3O5−
7 a polyarsenite, [O2As–O–As(O)–O–AsO2]
4O6−
9 a polyarsenite, [O2As–O–As(O)–O–As(O)–O–AsO2]
6O4−
11]
n, a polymeric anion
In all of these the geometry around the AsIII centers are approximately trigonal, the lone pair on the arsenic atom is stereochemically active. Well known examples of arsenites include sodium meta-arsenite which contains a polymeric linear anion, [AsO−
2]
n, and silver ortho-arsenite, Ag3AsO3, which contains the trigonal AsO3−
3 anion.
Arsenite ion aso3 3 lewis dot structure
Preparation of arsenites
Some arsenite salts can be prepared from an aqueous solution of As2O3. Examples of these are the meta-arsenite salts and at low temperature, hydrogen arsenite salts can be prepared, such as Na2(H2As4O8), NaAsO2·4H2O, Na2(HAsO3)·5H2O and Na5(HAsO3)(AsO3)·12H2O
Arsenite minerals
A number of minerals contain arsenite anions: reinerite, Zn3(AsO3)2; finnemanite, Pb5Cl(AsO3)3; paulmooreite, Pb2As2O5; stenhuggarite, CaFeSbAs2O7 (contains a complex polymeric anion); schneiderhöhnite, FeII
FeIII
3(As2O5)2AsO3; magnussonite, Mn5(OH)(AsO3)3; trippkeite, CuAs2O4; trigonite, Pb3Mn(AsO3)2(HAsO3); tooeleite, Fe6(AsO3)4SO4(OH)4·4H2O.
Arsenites in the environment
Arsenic can enter groundwater due to naturally occurring arsenic at deeper levels or from mine workings. Arsenic(III) can be removed from water by a number of methods, oxidation of AsIII to AsV for example with chlorine followed by coagulation with for example iron(III) sulfate. Other methods include ion-exchange and filtration. Filtration is only effective if arsenic is present as particulates, if the arsenite is in solution it passes though the filtration membrane.
Uses
Sodium arsenite is used in the water gas shift reaction to remove carbon dioxide. Fowler's solution first introduced in the 18th century was made up from As2O3 as a solution of potassium meta-arsenite, KAsO2.
Bacteria using and generating arsenite
Some species of bacteria obtain their energy by oxidizing various fuels while reducing arsenates to form arsenites. The enzymes involved are known as arsenate reductases.
In 2008, bacteria were discovered that employ a version of photosynthesis with arsenites as electron donors, producing arsenates (just like ordinary photosynthesis uses water as electron donor, producing molecular oxygen). The researchers conjectured that historically these photosynthesizing organisms produced the arsenates that allowed the arsenate-reducing bacteria to thrive.
In humans, arsenite inhibits pyruvate dehydrogenase (PDH complex) in the pyruvate–acetyl CoA reaction, and binds to the –SH group of lipoamide, a participant coenzyme. It also inhibits alpha ketoglutarate dehydrogenase, an enzyme of kreb's cycle. By both these inhibitions, arsenite poisoning affects energy production in the body.