8697. Sodium Tripolyphosphate

Nomenclature

CAS number: 7758-29-4
Triphosphoric acid pentasodium salt; sodium triphosphate; tripolyphosphate; STPP; poly; pentasodium triphosphate.
Na5O10P3; mol wt 367.86.
Na 31.25%, O 43.49%, P 25.26%.
Na5P3O10.

Description and references

Prepd by molecular dehydration of mono- and disodium phosphates: Audrieth, Bell, Inorg. Synth. 3, 85 (1950). Toxicity study: H. F. Smyth et al., Am. Ind. Hyg. Assoc. J. 30, 470 (1969).

Properties

Slightly hygroscopic granules. Soly in water (g/100 ml) at 25°: 20; at 100°: 86.5. pH of 1% soln at 25° = 9.7-9.8. Its properties are between those of tetrasodium pyrophosphate and sodium metaphosphate. Stability: With prolonged heating of STPP solns, it tends to revert to the orthophosphate. More stable than the higher (i.e., meta-) phosphates, but less stable than tetrasodium pyrophosphate. LD50 orally in rats: 6.50 g/kg (Smyth).

Caution

Moderately irritating to skin, mucous membranes. Ingestion can cause violent purging.

Use

In water softening (calcium and magnesium hardness is sequestered from soln without precipitation); peptizing agent, emulsifier and dispersing agent, ingredient of cleansers in drilling fluids to control mud viscosity in oil fields; as preservative, sequestrant and texturizer in foods.