Chemistry:Sodium phosphate
A sodium phosphate is a generic variety of salts of sodium (Na+
) and phosphate (PO3−
4). Phosphate also forms families or condensed anions including di-, tri-, tetra-, and polyphosphates. Most of these salts are known in both anhydrous (water-free) and hydrated forms. The hydrates are more common than the anhydrous forms.[1]
Uses
Sodium phosphates have many applications in food and for water treatment. For example, sodium phosphates are often used as emulsifiers (as in processed cheese),[2] thickening agents, and leavening agents for baked goods. They are also used to control pH of processed foods.[3] They are also used in medicine for constipation and to prepare the bowel for medical procedures. They are also used in detergents for softening water and as an efficient anti-rust solution.
Adverse effects
Sodium phosphates are popular in commerce in part because they are inexpensive and because they are nontoxic at normal levels of consumption.[4] However, oral sodium phosphates when taken at high doses for bowel preparation for colonoscopy may in some individuals carry a risk of kidney injury under the form of phosphate nephropathy. There are several oral phosphate formulations which are prepared extemporaneously. Oral phosphate prep drugs have been withdrawn in the United States, although evidence of causality is equivocal.[5] Since safe and effective replacements for phosphate purgatives are available, several medical authorities have recommended general disuse of oral phosphates.[6]
Monophosphates
Three families of sodium monophosphates are common, those derived from orthophosphate (PO3−
4), hydrogen phosphate (HPO2−
4), and dihydrogenphosphate (H
2PO−
4). Some of the best known salts are shown in the following table.
| name | formula | CAS registry number |
|---|---|---|
| monosodium phosphate (anhydrous) | NaH 2PO 4 |
7558-80-7 |
| monosodium phosphate monohydrate | NaH 2PO 4 · H2O |
10049-21-5 |
| monosodium phosphate dihydrate | NaH 2PO 4 · 2H2O |
13472-35-0 |
| disodium phosphate (anhydrous) | Na 2HPO 4 |
7558-79-4 |
| disodium phosphate dihydrate | Na 2HPO 4 · 2H2O |
10028-24-7 |
| disodium phosphate heptahydrate | Na 2HPO 4 · 7H2O |
7782-85-6 |
| disodium phosphate octahydrate | Na 2HPO 4 · 8H2O |
|
| disodium phosphate dodecahydrate | Na 2HPO 4 · 12H2O |
10039-32-4 |
| trisodium phosphate (anhydrous, hexagonal) | Na 3PO 4 |
|
| trisodium phosphate (anhydrous, cubic) | Na 3PO 4 |
7601-54-9 |
| trisodium phosphate hemihydrate | Na 3PO 4 · 0.5H2O |
|
| trisodium phosphate hexahydrate | Na 3PO 4 · 6H2O |
|
| trisodium phosphate octahydrate | Na 3PO 4 · 8H2O |
|
| trisodium phosphate dodecahydrate | Na 3PO 4 · 12H2O |
10101-89-0 |
Di- and polyphosphates
In addition to these phosphates, sodium forms a number of useful salts with pyrophosphates (also called diphosphates), triphosphates and high polymers. Of these salts, those of the diphosphates are particularly common commercially.
| name | formula | CAS Registry number |
|---|---|---|
| monosodium diphosphate (anhydrous) | NaH 3P 2O 7 |
|
| disodium diphosphate (anhydrous) | Na 2H 2P 2O 7 |
7758-16-9 |
| disodium diphosphate hexahydrate | Na 2H 2P 2O 7 · 6H2O |
|
| trisodium diphosphate (anhydrous) | Na 3HP 2O 7 |
|
| trisodium diphosphate monohydrate | Na 3HP 2O 7 · H2O |
|
| trisodium diphosphate nonahydrate | Na 3HP 2O 7 · 9H2O |
|
| tetrasodium diphosphate (anhydrous) | Na 4P 2O 7 |
7722-88-5 |
| tetrasodium diphosphate decahydrate | Na 4P 2O 7 · 10H2O |
13472-36-1 |
Beyond the diphosphates, sodium salts are known triphosphates, e.g. sodium triphosphate and tetraphosphates. The cyclic polyphosphates, called metaphosphates, include the trimer sodium trimetaphosphate and the tetramer, Na
3P
3O
9 and Na
4P
4O
12, respectively.
Polymeric sodium phosphates are formed upon heating mixtures of NaH
2PO
4 and Na
2HPO
4, which induces a condensation reaction. The specific polyphosphate generated depends on the details of the heating and annealing. One derivative is the glassy (i.e., amorphous) Graham's salt (sodium hexametaphosphate). It is a cyclic polyphosphate with the formula Na
6[(PO
3)
6]. Crystalline high molecular weight polyphosphates include Kurrol's salt and Maddrell's salt (CAS#10361-03-2). These species have the formula [NaPO
3]
n[NaPO
3(OH)]
2 where n can be as great as 2000, and it is a white powder practically insoluble in water. In terms of their structures, these polymers consist of PO−
3 units, with the chains are terminated by protonated phosphates.[1][7]
References
- ↑ 1.0 1.1 Klaus Schrödter; Gerhard Bettermann; Thomas Staffel; Friedrich Wahl; Thomas Klein; Thomas Hofmann (2012). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_465.pub3.
- ↑ "Monosodium Phosphate | Sodium Phosphate Formula". http://www.sodiumphosphateformula.com/tag/monosodium-phosphate.
- ↑ Lampila, Lucina E. (2013). "Applications and functions of food-grade phosphates". Ann. N.Y. Acad. Sci. 1301 (1): 37–44. doi:10.1111/nyas.12230. PMID 24033359. Bibcode: 2013NYASA1301...37L.
- ↑ Razzaque, M. S. (2011). "Phosphate toxicity: New insights into an old problem". Clinical Science 120 (3): 91–97. doi:10.1042/CS20100377. PMID 20958267.
- ↑ Markawitz, GB; Parezelli, MA (Aug 12, 2007), "Acute Phosphate Nephropathyl", Kidney Int. 76 (10): 1027–34, doi:10.1038/ki.2009.308, PMID 19675530
- ↑ Mackey, AC; Breen, L; Amand, KS; Evigan, M (August 2007), "Sodium phosphate tablets and acute Phosphate Nephropathy", Am J Gastroenterol 104 (8): 1903–6, doi:10.1038/ajg.2009.342, PMID 19661931, https://zenodo.org/record/1233245
- ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 530. ISBN 978-0-08-037941-8.
External links
- Bell, Russel N, "Sodium Aluminum Phosphate Cheese Emulsifying Agent", US patent 3726960, published 1973
- Lien, YH (16 July 2008). "Is bowel preparation before colonoscopy a risky business for the kidney?". Nature Clinical Practice Nephrology 4 (11): 606–14. doi:10.1038/ncpneph0939. PMID 18797448.
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