Phosphate

Phosphate

Names
IUPAC name Phosphate[1]
Other names Orthophosphate Tetraoxophosphate(V) Tetraoxidophosphate(V)
Identifiers
CAS Number	14265-44-2 Y
3D model ( JSmol )	Interactive image Interactive image Interactive image Interactive image
Beilstein Reference	3903772
ChEBI	CHEBI:18367 Y
ChemSpider	1032 Y
Gmelin Reference	1997
MeSH	Phosphates
PubChem CID	1061
UNII	NK08V8K8HR Y
InChI InChI=1S/H3O4P/c1-5(2,3)4/h(H3,1,2,3,4)/p-3 Y Key: NBIIXXVUZAFLBC-UHFFFAOYSA-K Y
SMILES [O-]P([O-])([O-])=O [O-]P(=O)([O-])[O-] O=P([O-])([O-])[O-] [O-] [P+]([O-])([O-])[O-]
Properties
Chemical formula	PO3− 4
Molar mass	94.9714 g mol−1
Conjugate acid	Monohydrogen phosphate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

In

H₃PO₄.

The phosphate or orthophosphate ion [PO
₄]³⁻
is derived from phosphoric acid by the removal of three protons H⁺
. Removal of one proton gives the dihydrogen phosphate ion [H
₂PO
₄]⁻
while removal of two protons gives the hydrogen phosphate ion [HPO
₄]²⁻
. These names are also used for salts of those anions, such as ammonium dihydrogen phosphate and trisodium phosphate.

• 
  H
  ₃PO
  ₄
  Phosphoric
  acid
• 
  [H
  ₂PO
  ₄]⁻
  
  Dihydrogen
  phosphate
• 
  [HPO
  ₄]²⁻
  
  Hydrogen
  phosphate
• 
  [PO
  ₄]³⁻
  
  Phosphate or orthophosphate

In organic chemistry, phosphate or orthophosphate is an organophosphate, an ester of orthophosphoric acid of the form PO
₄RR′R″ where one or more hydrogen atoms are replaced by organic groups. An example is trimethyl phosphate, (CH
₃)
₃PO
₄. The term also refers to the trivalent functional group OP(O-)
₃ in such esters. Phosphates may contain sulfur in place of one or more oxygen atoms (thiophosphates and organothiophosphates).

Orthophosphates are especially important among the various phosphates because of their key roles in biochemistry, biogeochemistry, and ecology, and their economic importance for agriculture and industry.^[2] The addition and removal of phosphate groups (phosphorylation and dephosphorylation) are key steps in cell metabolism.

Orthophosphates can condense to form pyrophosphates.

Chemical properties

The phosphate ion has a

, H
₃PO
₄.

Many phosphates are

ammonium phosphates

are all water-soluble. Most other phosphates are only slightly soluble or are insoluble in water. As a rule, the hydrogen and dihydrogen phosphates are slightly more soluble than the corresponding phosphates.

Equilibria in solution

In water solution, orthophosphoric acid and its three derived anions coexist according to the dissociation and recombination equilibria below^[3]

Equilibrium	Dissociation constant Ka[4]	pKa
H3PO4 ⇌ H2PO−4 + H+	${\displaystyle K_{a1}={\frac {[{\ce {H+}}][{\ce {H2PO4-}}]}{[{\ce {H3PO4}}]}}\approx 7.5\times 10^{-3}}$	pKa1 = 2.14
H2PO−4 ⇌ HPO2−4 + H+	${\displaystyle K_{a2}={\frac {[{\ce {H+}}][{\ce {HPO4^2-}}]}{[{\ce {H2PO4-}}]}}\approx 6.2\times 10^{-8}}$	pKa2 = 7.20
HPO2−4 ⇌ PO3−4 + H+	${\displaystyle K_{a3}={\frac {[{\ce {H+}}][{\ce {PO4^3-}}]}{[{\ce {HPO4^2-}}]}}\approx 2.14\times 10^{-13}}$	pKa3 = 12.37

Values are at 25 °C and 0 ionic strength.

The pK_a values are the

. At pH 1 or lower, the phosphoric acid is practically undissociated. Around pH 4.7 (mid-way between the first two pK_a values) the dihydrogen phosphate ion, [H
₂PO
₄]⁻
, is practically the only species present. Around pH 9.8 (mid-way between the second and third pK_a values) the monohydrogen phosphate ion, [HPO
₄]²⁻
, is the only species present. At pH 13 or higher, the acid is completely dissociated as the phosphate ion, (PO
₄)³⁻
.

This means that salts of the mono- and di-phosphate ions can be selectively crystallised from aqueous solution by setting the pH value to either 4.7 or 9.8.

In effect, H
₃PO
₄, H
₂(PO
₄)⁻
and H(PO
₄)²⁻
behave as separate

because the successive pK_a differ by more than 4.

Phosphate can form many polymeric ions such as pyrophosphate, (P
₂O
₇)⁴⁻
, and triphosphate, (P
₃O
₁₀)⁵⁻
. The various metaphosphate ions (which are usually long linear polymers) have an empirical formula of (PO
₃)⁻
and are found in many compounds.

Biochemistry of phosphates

In biological systems, phosphorus can be found as free phosphate anions in solution (inorganic phosphate) or bound to organic molecules as various organophosphates.

Inorganic phosphate is generally denoted P_i and at physiological (homeostatic) pH primarily consists of a mixture of [HPO
₄]²⁻
and [H
₂PO
₄]⁻
ions. At a neutral pH, as in the cytosol (pH = 7.0), the concentrations of the orthophoshoric acid and its three anions have the ratios

Thus, only [H
₂PO
₄]⁻
and [HPO
₄]²⁻
ions are present in significant amounts in the cytosol (62% [H
₂PO
₄]⁻
, 38% [HPO
₄]²⁻
). In extracellular fluid (pH = 7.4), this proportion is inverted (61% [HPO
₄]²⁻
, 39% [H
₂PO
₄]⁻
).

Inorganic phosphate can also be present as pyrophosphate anions [P
₂O
₇]⁴⁻
, which give orthophosphate by hydrolysis:

[P
₂O
₇]⁴⁻
+ H₂O ⇌ 2 [HPO
₄]²⁻

Organic phosphates are commonly found in the form of esters as

.

Bones and teeth

An important occurrence of phosphates in biological systems is as the structural material of bone and teeth. These structures are made of crystalline

ions.

Medical and biological research uses

Phosphates are medicinal salts of phosphorus. Some phosphates, which help cure many

Plant metabolism

Plants take up phosphorus through several pathways: the

arbuscular mycorrhizal

pathway and the direct uptake pathway.

Adverse health effects

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Hyperphosphatemia, or a high blood level of phosphates, is associated with elevated mortality in the general population. The most common cause of hyperphosphatemia in people, dogs, and cats is kidney failure. In cases of hyperphosphatemia, limiting consumption of phosphate-rich foods, such as some meats and dairy items and foods with a high phosphate-to-protein ratio, such as soft drinks, fast food, processed foods, condiments, and other products containing phosphate-salt additives is advised.^[6]

Phosphates induce vascular calcification, and a high concentration of phosphates in blood was found to be a predictor of cardiovascular events.^[7]

Production

Geological occurrence

Phosphates are the naturally occurring form of the element phosphorus, found in many phosphate minerals. In mineralogy and geology, phosphate refers to a rock or ore containing phosphate ions. Inorganic phosphates are mined to obtain phosphorus for use in agriculture and industry.^[2]

The largest global producer and exporter of phosphates is

, Tunisia, Togo, and Jordan, countries that have large phosphate-mining industries.

Phosphorite mines are primarily found in:

• North America:
  Main article: Phosphate mining in the United States
  United States, especially Florida, with lesser deposits in North Carolina, Idaho, and Tennessee
• Africa: Morocco, Algeria, Egypt, Niger, Senegal, Togo, Tunisia, Mauritania
• Middle East: Saudi Arabia, Jordan, Israel, Syria, Iran and Iraq, at the town of Akashat, near the Jordanian border.
• Central Asia: Kazakhstan
• Oceania:
  Banaba Island

In 2007, at the current rate of consumption, the supply of phosphorus was estimated to run out in 345 years.

are mainly hydroxyapatite and fluoroapatite, phosphate minerals contain roughly 18.5% phosphorus by weight. If phosphate rock contains around 20% of these minerals, the average phosphate rock has roughly 3.7% phosphorus by weight.

Some phosphate rock deposits, such as Mulberry in Florida,^[14] are notable for their inclusion of significant quantities of radioactive uranium isotopes. This is a concern because radioactivity can be released into surface waters^[15] from application of the resulting phosphate fertilizer.

In December 2012,

Around 2018, Norway discovered phosphate deposits almost equal to those in the rest of Earth combined.[17]^[18]

In July 2022 China announced quotas on phosphate exportation.^[19]

The largest importers in millions of metric tons of phosphate are Brazil 3.2, India 2.9 and the USA 1.6.^[20]

Mining

The three principal phosphate producer countries (China, Morocco and the United States) account for about 70% of world production.

Production and global reserves of natural phosphate by country in 2019
(USGS, 2021)^[21]

Country	Production (millions kg)	Share of global production (%)	Reserves (millions kg)
Algeria	1,300	0.54	2,200,000
Australia	2,700	1.17	1,100,000
Brazil	4,700	3.00	1,600,000
China	95,000	44.83	3,200,000
Egypt	5,000	2.47	2,800,000
Finland	995	-	1,000,000
India	1,480	0.49	46,000
Iraq	200	0.09	430,000
Israel	2,810	1.48	57,000
Jordan	9,220	3.36	800,000
Kazakhstan	1,500	0.72	260,000
Mexico	558	0.76	30,000
Morocco and Western Sahara	35,500	13.45	50,000,000
Peru	4,000	1.79	210,000
Russia	13,100	5.60	600,000
Saudi Arabia	6,500	1.48	1,400,000
Senegal	3,420	0.45	50,000
South Africa	2,100	0.99	1,400,000
Syria	2,000	0.34	1,800,000
Togo	800	0.45	30,000
Tunisia	4,110	1.79	100,000
Uzbekistan	900	-	100,000
United States	23,300	12.37	1,000,000
Vietnam	4,650	1.21	30,000
Other countries	1,140	1.17	840,000
Total	227,000	100	71,000,000

Ecology

In ecological terms, because of its important role in biological systems, phosphate is a highly sought after resource. Once used, it is often a limiting nutrient in

Calcium hydroxyapatite and calcite precipitates can be found around

Phosphate deposits can contain significant amounts of naturally occurring heavy metals. Mining operations processing

See also

References

External links

Wikimedia Commons has media related to Phosphates.

• US Minerals Databrowser provides data graphics covering consumption, production, imports, exports and price for phosphate and 86 other minerals
• Phosphate: analyte monograph – The Association for Clinical Biochemistry and Laboratory Medicine