Sodium phosphates

Sodium Dihydrogen Phosphate

Sodium Hydrogen Phosphate

Sodium Phosphate

Sodium phosphate is a generic term for a variety of salts of Na⁺ and phosphate (PO₄^3-)). 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 the food industry and for water treatment. For example, sodium phosphates are often used as leavening agents for baked goods. They are used to control pH of processed foods.^[2] They are also used in medicine for constipation and to prepare the bowel for medical procedures.

Adverse effects

Sodium phosphates are popular in commerce in part because they are inexpensive and nontoxic.

Oral sodium phosphates 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 Oral phosphate prep drugs have been withdrawn in the United States, although evidence of causality is equivocal.^[3] Since safe and effective replacements for phosphate purgatives are available, several medical authorities have recommended general disuse of oral phosphates.^[4]

Monophosphates

Three families of sodium monophosphates are common, those derived from orthophosphate (PO₄^3-), hydrogen phosphate (HPO₄^-), and dihydrogenphosphate (H₂PO₄^-). Some of the most well known salt are shown in the table.

Di- and polyphosphates

In addition to these phosphates, sodium forms a number of useful salts with pyrophosphates (called diphosphates), triphosphates and high polymers. Of these salts, those of the diphosphates are particularly common commercially.

Beyond the diphosphates, sodium salts are known triphosphates, e.g. sodium triphosphate and tetraphospates. The cyclic polyphosphates, called metaphosphates, include the trimer sodium trimetaphosphate and the tetramer, Na₃P₃O₉ and Na₄P₄O₁₂, respectively.

Polymeric sodium phosphates are formed upon heating mixtures of NaH₂PO₄ and Na₂HPO⁴, which induces condensation. The specific polyphosphate generated depends on the details of the heating and annealling. One derivative is the glassy (i.e., amorphous) Graham’s salt. Crystalline high molecular weight polyphosphates include Kurrol’s salt and Maddrell’s salt (CAS#10361-03-2). These species have the formula [NaPO₃]_n[NaPO₃(OH)]₂ where n can be as great as 2000. In terms of their structures, these polymers consist of PO₃^- "monomers", with the chains are terminated by protonated phosphates.^[1]

References

1. ↑ 1.0 1.1 Klaus Schrödter, Gerhard Bettermann, Thomas Staffel, Friedrich Wahl, Thomas Klein, Thomas Hofmann "Phosphoric Acid and Phosphates" in Ullmann’s Encyclopedia of Industrial Chemistry 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_465.pub3
2. ↑ Lucina E. Lampila "Applications and functions of food-grade phosphates" Ann. N.Y. Acad. Sci. 2013, vol. 1301, pp. 37–44. doi:10.1111/nyas.12230
3. ↑ Markowitz, GS; Perazella, MA (Aug 12, 2009), "Acute Phosphate Nephropathy", Kidney Int. 76 (10): 1027–34, doi:10.1038/ki.2009.308, PMID 19675530 
4. ↑ Mackey, AC; Green, L; Amand, KS; Avigan, M (2009), "Sodium phosphate tablets and acute Phosphate Nephropathy", Am J Gastroenterol (Aug) 104 (8): 1903–6, doi:10.1038/ajg.2009.342, PMID 19661931  Check date values in: |publicationdate= (help)

External links

• Bell, Russel N (1973), "SODIUM ALUMINUM PHOSPHATE CHEESE EMULSIFYING AGENT", US Patent 3726960 (April)  Check date values in: |publicationdate= (help)
• Lien, YH (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.