Sodium trimetaphosphate[1]
Other names
Sodium trimetaphosphate
  • 7785-84-4 checkY
3D model (JSmol)
ECHA InfoCard 100.029.171 Edit this at Wikidata
EC Number
  • 232-088-3
  • InChI=1S/3Na.H3O9P3/c;;;1-10(2)7-11(3,4)9-12(5,6)8-10/h;;;(H,1,2)(H,3,4)(H,5,6)/q3*+1;/p-3
  • O=P(OP(O1)([O-])=O)([O-])OP1([O-])=O.[Na+].[Na+].[Na+]
Molar mass 305.885 g/mol
Appearance colorless or white crystals
Density 2.49 g/cm3 (anhydrous)
1.786 g/cm3 (hexahydrate)
Melting point 53 °C (127 °F; 326 K) (hexahydrate, decomposes to anyhdrous)
22 g/100 mL
Solubility insoluble in alcohol
1.433 (hexahydrate)
triclinic (hexahydrate)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Sodium trimetaphosphate (also STMP), with formula Na3P3O9, is a metaphosphate of sodium. It has the empirical formula NaPO3. It is the sodium salt of trimetaphosphoric acid. It is a colourless solid that finds specialised applications in food and construction industries. STMP is prepared by heating samples sodium polyphosphate. [2]

Although drawn with a particular resonance structure, the trianion has D3d symmetry.[3] Hydrolysis of the ring leads to the acyclic sodium triphosphate:

Na3P3O9 + H2O → H2Na3P3O10

The main reactions of the triphosphate anion is ring-opening by nucleophiles, including amines.[4]


  1. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. pp. 4–86. ISBN 0-8493-0594-2.
  2. ^ Klaus Schrödter; Gerhard Bettermann; Thomas Staffel; Friedrich Wahl; Thomas Klein; Thomas Hofmann (2008). "Phosphoric Acid and Phosphates". Ullmann's Encyclopedia of Industrial Chemistry. Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_465.pub3. ISBN 978-3527306732.
  3. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 530. ISBN 978-0-08-037941-8.
  4. ^ Bezold, Dominik; Dürr, Tobias; Singh, Jyoti; Jessen, Henning J. (2020). "Cyclotriphosphate: A Brief History, Recent Developments, and Perspectives in Synthesis". Chemistry – A European Journal. 26 (11): 2298–2308. doi:10.1002/chem.201904433. PMC 7065162. PMID 31637774.