Sodium trimetaphosphate

Sodium trimetaphosphate
Names
	Other names Sodium trimetaphosphate
Identifiers
CAS Number	7785-84-4 ;
3D model (JSmol)	Interactive image;
ECHA InfoCard	100.029.171
EC Number	232-088-3;
PubChem CID	24579;
UNII	3IH6169RL0 ;
CompTox Dashboard (EPA)	DTXSID7052789 ;
	InChI 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;
	SMILES O=P(OP(O1)([O-])=O)([O-])OP1([O-])=O.[Na+].[Na+].[Na+];
Properties
Chemical formula	Na3P3O9
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)
Solubility in water	22 g/100 mL
Solubility	insoluble in alcohol
Refractive index (nD)	1.433 (hexahydrate)
Structure
Crystal structure	triclinic (hexahydrate)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Sodium trimetaphosphate (also STMP), with formula Na₃P₃O₉, is one of the metaphosphates of sodium. It has the formula Na₃P₃O₉ but the hexahydrate Na₃P₃O₉·(H₂O)₆ 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: it is used as a phosphorylating agent for ascorbic acid to stabilize vitamin C mixtures against thermal decomposition; in the construction industry, sodium trimetaphosphate is used to prevent the shrinkage of gypsum plaster boards (US Pat. 03/0154888) and as a setting retarder for gypsum plaster.

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