Sodium trimetaphosphate (also STMP), with formula Na₃P₃O₉, is one of the

metaphosphate A metaphosphate ion is an oxyanion that has the empirical formula . It was first postulated in 1955 but was not observed until 1979, when it was detected by mass spectrometry. Metaphosphate is an intermediate in the hydrolysis of phosphate esters b ...

s of

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...

. It has the formula but the

hexahydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

is also well known. It is the sodium

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...

of trimetaphosphoric acid. It is a colourless solid that finds specialised applications in food and construction industries. Although drawn with a particular resonance structure, the trianion has high

symmetry Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...

Synthesis and reactions

Sodium dihydrogen phosphate is heated at 550 °C to give anhydrous trisodium trimetaphosphate: : The latter dissolves in water and precipitated by the addition of sodium chloride (

common ion effect The common-ion effect refers to the decrease in solubility of an ionic precipitate by the addition to the solution of a soluble compound with an ion in common with the precipitate. This behaviour is a consequence of Le Chatelier's principle for the ...

), affording the hexahydrate. STMP can also prepared by heating samples sodium polyphosphate. Hydrolysis of the ring leads to the acyclic sodium triphosphate: :Na₃P₃O₉ + H₂O → H₂Na₃P₃O₁₀ The analogous reaction of the metatriphosphate anion involves ring-opening by

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...

nucleophiles.

References

Food additives Sodium compounds Metaphosphates {{Sodium compounds