Sodium triphosphate

Sodium triphosphate

Names
IUPAC name Pentasodium triphosphate
Other names sodium tripolyphosphate, polygon, STPP
Identifiers
CAS Number	7758-29-4 Y
ECHA InfoCard	100.028.944
E number	E451 (thickeners, ...)
PubChem	517047
RTECS number	YK4570000
UNII	9SW4PFD2FZ N
Properties
Chemical formula	Na5P3O10
Molar mass	367.864 g/mol
Appearance	white powder
Density	2.52 g/cm3
Melting point	622 °C (1,152 °F; 895 K)
Solubility in water	14.5 g/100 mL (25 °C)
Hazards
Safety data sheet	ICSC 1469
NFPA 704	0 2 0
Flash point	Non-flammable
Related compounds
Other anions	Trisodium phosphate Tetrasodium pyrophosphate Sodium hexametaphosphate
Other cations	Pentapotassium triphosphate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Sodium triphosphate (STP), also sodium tripolyphosphate (STPP), or tripolyphosphate (TPP),) is an inorganic compound with formula Na₅P₃O₁₀. It is the sodium salt of the polyphosphate penta-anion, which is the conjugate base of triphosphoric acid. It is produced on a large scale as a component of many domestic and industrial products, especially detergents. Environmental problems associated with eutrophication are attributed to its widespread use.

Sodium tripolyphosphate is produced by heating a stoichiometric mixture of disodium phosphate, Na₂HPO₄, and monosodium phosphate, NaH₂PO₄, under carefully controlled conditions.

In this way, approximately 2 million tons are produced annually.

STPP is a colourless salt, which exists both in anhydrous form and as the hexahydrate. The anion can be described as the pentanionic chain [O₃POP(O)₂OPO₃]⁵⁻. Many related di-, tri-, and polyphosphates are known including the cyclic triphosphate P₃O₉³⁻. It binds strongly to metal cations as both a bidentate and tridentate chelating agent.

The majority of STPP is consumed as a component of commercial detergents. It serves as a "builder," industrial jargon for a water softener. In hard water (water that contains high concentrations of Mg²⁺ and Ca²⁺), detergents are deactivated. Being a highly charged chelating agent, TPP⁵⁻ binds to dications tightly and prevents them from interfering with the sulfonate detergent.

STPP is a preservative for seafood, meats, poultry, and animal feeds. It is common in food production as E number E451. In foods, STPP is used as an emulsifier and to retain moisture. Many governments regulate the quantities allowed in foods, as it can substantially increase the sale weight of seafood in particular. The United States Food and Drug Administration lists STPP as "generally recognized as safe."