Sodium hexametaphosphate

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Sodium hexametaphosphate[1]
Skeletal formula of sodium hexametaphosphate
CAS number 10124-56-8 YesY
PubChem 24968
ChemSpider 23340 N
EC number 233-343-1
MeSH sodium+polymetaphosphate
Jmol-3D images Image 1
Molecular formula 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 in water soluble
Solubility insoluble in organic solvents
Refractive index (nD) 1.482
S-phrases S24/25
Main hazards Irritant
LD50 3.053 g kg−1
Related compounds
Other anions Trisodium phosphate
Tetrasodium pyrophosphate
Pentasodium triphosphate
Related compounds Sodium trimetaphosphate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

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. It is more correctly termed sodium polymetaphosphate. It is prepared by heating monosodium orthophosphate, according to the reaction:

Heating this salt above 169 °C gives the corresponding sodium acid pyrophosphate:

2 NaH2PO4 → Na2H2P2O7 + H2O

Subsequently, heat the pyrophosphate at 620 °C gives the corresponding sodium hexametaphosphate:

3Na2H2P2O7 → (NaPO3)6 + 3H2O

followed by rapid cooling. SHMP hydrolyzes in aqueous solution, particularly under acidic conditions, to sodium trimetaphosphate and sodium orthophosphate.


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. Also used as a dispersing agent to break down clay and other soil types.

One of the lesser-known uses for sodium hexametaphosphate is as a deflocculant in the making of terra sigillata, a ceramic technique using a fine particled slip. The sodium hexametaphosphate or another deflocculant allows the clay particles of an ordinary slip to remain suspended for an extended period of time; after 24hrs or more, the slip separates into layers with the larger particles at the bottom, and the finest particles can be siphoned off and applied to a green ware ceramic surface. It is also used as a deflocculant or dispersant for the ASTM D422 - 63(2007) Standard Test Method for Particle-Size Analysis of Soils.

It can be prepared from Na2HPO4 and NaH2PO4.[citation needed]

It is currently used as an active ingredient in Crest Pro-Health as a claimed anti-staining and tartar prevention ingredient.[3]

Sodium hexametaphosphate in foods[edit]

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 sodium hexametaphosphate. [4]


  1. ^ Merck Index, 12th Edition, Sodium polymetaphosphate, 8814
  2. ^ Van Wazer, John R. Phosphorus and its compounds. New York : Interscience Publishers (1958)
  3. ^
  4. ^

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