Sodium hexametaphosphate[1]
Skeletal formula of sodium hexametaphosphate
IUPAC name
sodium cyclo-hexaphosphate
Other names
Calgon S

Glassy sodium
Graham's salt
Hexasodium metaphosphate

Metaphosphoric acid, hexasodium salt
3D model (JSmol)
ECHA InfoCard 100.030.299 Edit this at Wikidata
EC Number
  • 233-343-1
MeSH sodium+polymetaphosphate
  • InChI=1S/6Na.H6O18P6/c;;;;;;1-19(2)13-20(3,4)15-22(7,8)17-24(11,12)18-23(9,10)16-21(5,6)14-19/h;;;;;;(H,1,2)(H,3,4)(H,5,6)(H,7,8)(H,9,10)(H,11,12)/q6*+1;/p-6 ☒N
  • [O-]P1(=O)OP(=O)([O-])OP(=O)([O-])OP(=O)(OP(=O)(OP(=O)(O1)[O-])[O-])[O-].[Na+].[Na+].[Na+].[Na+].[Na+].[Na+]
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)
Solubility insoluble in organic solvents
Occupational safety and health (OHS/OSH):
Main hazards
GHS labelling:[2]
GHS07: Exclamation mark
Lethal dose or concentration (LD, LC):
3.053 g kg−1
Safety data sheet (SDS)
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).
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Sodium hexametaphosphate (SHMP) is a salt of composition Na6[(PO3)6].[3] Sodium hexametaphosphate of commerce is typically a mixture of metaphosphates (empirical formula: NaPO3), 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. They are white solids that dissolve in water.


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.[4][5][6][7] It is also used as a dispersing agent to break down clay and other soil types for soil texture assessment.[8]

It is used as an active ingredient in toothpastes as an anti-staining and tartar prevention ingredient.[9]

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 drinks, among other foods, can contain SHMP.[10][11][12]

Water softener salt

SHMP is used in Diamond Crystal brand Bright & Soft Salt Pellets for water softeners in a concentration of 0.03%. It is the only additive other than sodium chloride.


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.


SHMP hydrolyzes in aqueous solution, particularly under acidic conditions and/or heat, to sodium trimetaphosphate and sodium orthophosphate.[13]


Sodium hexametaphosphate is the alkali salt of one of the series of polymetaphosphoric acids (acids formed by the polymerization of phosphate groups).[14] Hexametaphosphoric acid was first made in 1825 by the German chemist Johann Frederich Philipp Engelhart (1797-1853).[15] For his doctoral thesis, Engelhart intended to determine whether iron was responsible for the red color of blood. In order to purify his blood samples, Engelhart had found that he could coagulate the blood serum's albumin (dissolved proteins) by treating the blood with phosphoric acid. This contradicted the findings of the famous Swedish chemist Jöns Jacob Berzelius, who had stated that phosphoric acid did not coagulate water-soluble proteins such as egg white.[16] Berzelius and Engelhart collaborated with the intention of resolving the contradiction; they concluded that Engelhart had produced a new form of phosphoric acid simply by burning phosphorus in air and then dissolving the resulting substance in water.[17] However they did not determine the new acid's composition. That analysis was accomplished in 1833 by the Scottish chemist Thomas Graham, who named the sodium salt of the new acid "metaphosphate of soda".[18] Graham's findings were confirmed by the German chemists Justus von Liebig and Theodor Fleitmann.[19] In 1849 Fleitmann coined the name "hexametaphosphoric acid".[20][21]

By 1956, chromatographic analysis of hydrolysates of Graham's salt (sodium polyphosphate) indicated the presence of cyclic anions containing more than four phosphate groups;[22] these findings were confirmed in 1961.[23] In 1963, the German chemists Erich Thilo and Ulrich Schülke succeeded in preparing sodium hexametaphosphate by heating anhydrous sodium trimetaphosphate.[24]


Sodium phosphates are recognized to have low acute oral toxicity. SHMP concentrations not exceeding 10,000mg/L or mg/kg are considered protective levels by the EFSA and USFDA. Extreme concentrations of this salt may cause acute side effects from excessive blood serum concentrations of sodium, such as: “irregular pulse, bradycardia, and hypocalcemia."[25]


  1. ^ Merck Index, 12th Edition, Sodium polymetaphosphate, 8814
  2. ^ "C&L Inventory".
  3. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 530. ISBN 978-0-08-037941-8.
  4. ^ 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.
  5. ^ 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)
  6. ^ 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
  7. ^ 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.
  8. ^ ASTM D422 – 63(2007) Standard Test Method for Particle-Size Analysis of Soils.
  9. ^ "Crest Pro-Health Frequently Asked Questions". Archived from the original on 2012-11-19. Retrieved 2012-11-20.
  10. ^ "Ingredient Results - Sodium Hexametaphosphate".
  11. ^ "Food Additives & Ingredients - Food Additive Status List". Food and Drug Administration. 26 August 2021.
  12. ^ "CFR - Code of Federal Regulations Title 21".
  13. ^ Van Wazer, John (1958). Phosphorus and its Compounds. New York: Interscience Publishers. Retrieved 7 April 2015.
  14. ^ Mehrotra, R.C. (1975). "Synthesis and properties of simple and complex polymetaphosphate glasses of alkali metals". Pure and Applied Chemistry. 44 (2): 201-220. doi:10.1351/pac197544020201.
  15. ^ Stanley, Michael (November 1979) "The Chemical Work of Thomas Graham" Ph.D. thesis (The Open University, Milton Keynes, England, UK), p. 151.
  16. ^ Engelhart, Johann Friedrich (1825) "Commentatio de vera materiae sanguini purpureum colorem impertientis natura" [Commentary on the true nature of the substance of blood which imparts its purple color] Ph.D. thesis (University of Göttingen, Göttingen, Germany),(in Latin), pp. 40-42.
  17. ^ Berzelius (1827). "Sonderbare Verhalten der Phosphorsäure zur Eiweiss" [Strange behavior of phosphoric acid toward egg white]. Annalen der Physik und Chemie. 2nd series (in German). 9: 631–632.
  18. ^ Graham, Thomas (1833). "Researches on the arseniates, phosphates, and modifications of phosphoric acid". Philosophical Transactions of the Royal Society of London: 253–284. See p. 277.
  19. ^ Liebig, Justus (April 1838). "Ueber die Constitution der organischen Säuren" [On the composition of organic acids]. Annalen der Pharmacie (in German). 26: 113–189. See p. 142.
    • Reprinted in French: Liebig, J. (1838). "Sur la constitution des acides organiques" [On the composition of organic acids]. Annales de Chimie. 2nd series (in French). 68: 5–93. See p. 39.
    • See also: Stanley (1979) p. 186ff, footnote 162.
  20. ^ 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. 239, Fleitmann coined the name Hexametaphosphorsäure (hexametaphosphoric acid).
  21. ^ 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.
  22. ^ 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.
  23. ^ (Thilo & Schülke, 1963a), p. 1175.
  24. ^ 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. Bibcode:1963AngCh..75.1175T. doi:10.1002/ange.19630752305.
    • Thilo, E.; Schülke, U. (1963b). "Preparation of true sodium hexametaphosphate Na6[P6O18]". Angewandte Chemie International Edition. 2 (12): 742. doi:10.1002/anie.196307421.
  25. ^ Schrödter, Klaus; Bettermann, Gerhard; Staffel, Thomas; Wahl, Friedrich; Klein, Thomas; Hofmann, Thomas (2008). "Phosphoric Acid and Phosphates". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_465.pub3. ISBN 978-3527306732.