Sodium trimetaphosphate explained

Sodium trimetaphosphate (also STMP), with formula Na3P3O9, is one of the metaphosphates of sodium. It has the formula but the hexahydrate is also well known. It is the sodium salt of trimetaphosphoric acid. It is a colourless solid that finds specialised applications in food and construction industries.[1]

Although drawn with a particular resonance structure, the trianion has high symmetry.

Synthesis and reactions

Trisodium trimetaphosphate is produced industrially by heating sodium dihydrogen phosphate to 550 °C, a method first developed in 1955:[2]

The trimetaphosphate dissolves in water and is precipitated by the addition of sodium chloride (common ion effect), affording the hexahydrate.[3] STMP can also prepared by heating samples of sodium polyphosphate,[1] or by a thermal reaction of orthophosphoric acid and sodium chloride at 600°C.[4] [5]

Hydrolysis of the ring leads to the acyclic sodium triphosphate:

Na3P3O9 + H2O → H2Na3P3O10The analogous reaction of the metatriphosphate anion involves ring-opening by amine nucleophiles.[6]

Notes and References

  1. Book: Klaus Schrödter. Gerhard Bettermann. Thomas Staffel. Friedrich Wahl. Thomas Klein. Thomas Hofmann. Ullmann's Encyclopedia of Industrial Chemistry. Phosphoric Acid and Phosphates. Ullmann’s Encyclopedia of Industrial Chemistry. 2008. Wiley-VCH. Weinheim. 10.1002/14356007.a19_465.pub3. 978-3527306732. 94458523 .
  2. Thilo . Erich . Grunze . Herbert . Zur Chemie der kondensierten Phosphate und Arsenate. XIII. Der Entwässerungsverlauf der Dihydrogenmonophosphate des Li, Na, K, und NH4. . Zeitschrift für anorganische und allgemeine Chemie . December 1955 . 281 . 5–6 . 262–283 . 10.1002/zaac.19552810504.
  3. Book: 10.1002/9780470132340.ch26. Sodium Metaphosphates . 1950 . Bell . R. N. . Inorganic Syntheses . 103–106 . 9780470132340. 3 .
  4. Minh . Doan Pham . Ramaroson . Jocelyn . Nzihou . Ange . Sharrock . Patrick . Depelsenaire . Guy . A New Route for the Synthesis of Alkali Polyphosphate from Economical Starting Materials: Preparation and Characterization of Sodium Cyclotriphosphate . Phosphorus, Sulfur, and Silicon and the Related Elements . 1 January 2012 . 187 . 1 . 112–120 . 10.1080/10426507.2011.590950. 98164275 .
  5. Pham Minh . Doan . Ramaroson . Jocelyn . Nzihou . Ange . Sharrock . Patrick . One-Step Synthesis of Sodium Trimetaphosphate (Na 3 P 3 O 9) from Sodium Chloride and Orthophosphoric Acid . Industrial & Engineering Chemistry Research . 14 March 2012 . 51 . 10 . 3851–3854 . 10.1021/ie201085b. 98235073 .
  6. 10.1002/chem.201904433. Cyclotriphosphate: A Brief History, Recent Developments, and Perspectives in Synthesis. 2020. Bezold. Dominik. Dürr. Tobias. Singh. Jyoti. Jessen. Henning J.. Chemistry – A European Journal. 26. 11. 2298–2308. 31637774. 7065162.

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