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

. It has the formula but the hexahydrate 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 quanti ...

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. Na3P3O9(H2O)3(CollCode345)

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), affording the hexahydrate. STMP can also prepared by heating samples

sodium polyphosphate Polyphosphates are salts or esters of polymeric oxyanions formed from tetrahedral PO4 (phosphate) structural units linked together by sharing oxygen atoms. Polyphosphates can adopt linear or a cyclic ring structures. In biology, the polyphosphate e ...

. 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 Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent su ...

nucleophiles.

References

Food additives Sodium compounds Metaphosphates {{Sodium compounds