Sodium hexametaphosphate

Sodium hexametaphosphate (SHMP) is a hexamer of composition (NaPO3)6.[2] Sodium hexametaphosphate of commerce is typically a mixture of polymeric metaphosphates, of which the hexamer is one, and is usually the compound referred to by this name. Such a mixture is more correctly termed sodium polymetaphosphate.

Sodium hexametaphosphate[1]
Names
Other names
Calgon S

Glassy sodium
Graham's salt
Hexasodium metaphosphate

Metaphosphoric acid, hexasodium salt
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.299
EC Number
  • 233-343-1
MeSH sodium+polymetaphosphate
Properties
Na
6P
6O
18
Molar mass 611.7704 g mol−1
Appearance White crystals
Odor odorless
Density 2.484 g/cm3
Melting point 628 °C (1,162 °F; 901 K)
Boiling point 1,500 °C (2,730 °F; 1,770 K)
soluble
Solubility insoluble in organic solvents
1.482
Hazards
Main hazards Irritant
Safety data sheet hazard.com
S-phrases (outdated) S24/25
Lethal dose or concentration (LD, LC):
3.053 g kg−1
Related compounds
Other anions
 Trisodium phosphate
Tetrasodium pyrophosphate
Pentasodium triphosphate
Related compounds
 Sodium trimetaphosphate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Uses

SHMP is used as a sequestrant and has applications within a wide variety of industries, including as a food additive in which it is used under the E number E452i. Sodium carbonate is sometimes added to SHMP to raise the pH to 8.0–8.6, which produces a number of SHMP products used for water softening and detergents.

A significant use for sodium hexametaphosphate is as a deflocculant in the production of clay-based ceramic particles.[3][4][5][6] It is also used as a dispersing agent to break down clay and other soil types for soil texture assessment.[7]

It is used as an active ingredient in toothpastes as an anti-staining and tartar prevention ingredient.[8]

Food additive

As a food additive, SHMP is used as an emulsifier. Artificial maple syrup, canned milk, cheese powders and dips, imitation cheese, whipped topping, packaged egg whites, roast beef, fish fillets, fruit jelly, frozen desserts, salad dressing, herring, breakfast cereal, ice cream, beer, and bottled beverages, among other foods, can contain SHMP.[9][10][11]

Preparation

SHMP is prepared by heating monosodium orthophosphate to generate sodium acid pyrophosphate:

2 NaH2PO4 → Na2H2P2O7 + H2O

Subsequently, the pyrophosphate is heated to give the corresponding sodium hexametaphosphate:

3 Na2H2P2O7 → (NaPO3)6 + 3 H2O

followed by rapid cooling.

Reactions

SHMP hydrolyzes in aqueous solution, particularly under acidic conditions, to sodium trimetaphosphate and sodium orthophosphate.[12]

History

Hexametaphosphoric acid was named (but misidentified) in 1849 by the German chemist Theodor Fleitmann (1828–1904).[13][14] By 1956, chromatographic analysis of hydrolysates of Graham's salt (sodium polyphosphate) indicated the presence of cyclic anions containing more than four phosphate groups;[15] these findings were confirmed in 1961.[16] In 1963, the German chemists Erich Thilo and Ulrich Schülke succeeded in preparing sodium hexametaphosphate by heating anhydrous sodium trimetaphosphate.[17]

References
  1. Merck Index, 12th Edition, Sodium polymetaphosphate, 8814
  2. Van Wazer, John R. Phosphorus and its compounds. New York : Interscience Publishers (1958)
  3. The Role Of Sodium Hexametaphosphate In The Dissolution Process Of Kaolinite And KaolinF. Andreola; E.Castellini; T.Manfredini; M.Romagnoli. Journal of the European Ceramic Society, Volume 24, Number 7, June 2004.
  4. Impact Of Dispersants On The Mechanical Strength Development Of Alumina-Spinel Self-Flowing Refractory Castables. Sasan Otroj, Mohammad Reza Nilforushan, Arash Daghighi, Reza Marzban. Ceramics – Silikáty 54 (3) 284–289 (2010)
  5. Effect Of Adding Sodium Hexametaphosphate Liquefier On Basic Properties Of Calcium Phosphate Cements. S. Hesaraki; A. Zamanian; F. Moztarzadeh. Journal of Biomedical Materials Research Part A. Vol. 88A, No. 2, 2009
  6. Study Of Clay’s Mineralogy Effect On Rheological Behavior Of Ceramic Suspensions Using An Experimental Design. Afef Jmal Ayadi; Julien Soro; Amel Kamoun; Samir Baklouti. International Journal of Recent Research and Applied Studies 14 (2). February 2013.
  7. ASTM D422 – 63(2007) Standard Test Method for Particle-Size Analysis of Soils.
  8. Crest Pro-Health Frequently Asked Questions
  9. "Ingredient Results - Sodium Hexametaphosphate".
  10. "Food Additives & Ingredients - Food Additive Status List".
  11. "CFR - Code of Federal Regulations Title 21".
  12. Van Wazer, John (1958). Phosphorus and its Compounds. New York: Interscience Publishers. Retrieved 7 April 2015.
  13. Fleitmann, Th. (1849). "Ueber die verschiedenen Metaphosphorsäuren und zwei neue Säuren derselben Verbindungsproportion" [On various metaphosphoric acids and two new acids of the same compound proportion]. Annalen der Physik und Chemie. 2nd series (in German). 78: 233–260, 338–366. On p. 249, Fleitmann coined the name Hexametaphosphorsäure (hexametaphosphoric acid).
  14. Griffith, E.J.; Buxton, R.L. (1965). "The preparation and properties of the twelve-membered ring hexametaphosphate anion". Inorganic Chemistry. 4 (4): 549–551. doi:10.1021/ic50026a023. ; see p. 549.
  15. Van Wazer, J. R.; Kroupa, E. Karl (1956). "Existence of ring phosphates higher than tetrametaphosphate". Journal of the American Chemical Society. 78 (8): 1772. doi:10.1021/ja01589a086.
  16. (Thilo & Schülke, 1963a), p. 1175.
  17. See:
    • Thilo, E.; Schülke, U. (1963a). "Darstellung des echten Natrium-hexametaphosphates Na6[P6O18]" [Preparation of true sodium hexametaphosphate Na6[P6O18]]. Angewandte Chemie (in German). 75 (23): 1175–1176. doi:10.1002/ange.19630752305.
    • Thilo, E.; Schülke, U. (1963b). "Preparation of true sodium hexametaphosphate Na6[P6O18]". Angewandte Chemie International Edition. 2 (12): 742.
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