Sodium acid pyrophosphate

Disodium pyrophosphate
Names

IUPAC name Disodium dihydrogen diphosphate
Other names Diphosphoric acid, disodium salt Disodium dihydrogen pyrophosphate Disodium diphosphate Sodium acid pyrophosphate, SAPP
Identifiers
CAS Number	7758-16-9^Y
3D model (Jmol)	Interactive image
ChemSpider	22859^N
ECHA InfoCard	100.028.941
EC Number	231-835-0
PubChem	24451
UNII	H5WVD9LZUD^Y
InChI InChI=1S/2Na.H4O7P2/c;;1-8(2,3)7-9(4,5)6/h;;(H2,1,2,3)(H2,4,5,6)/q2+1;/p-2^N Key: GYQBBRRVRKFJRG-UHFFFAOYSA-L^N InChI=1/2Na.H4O7P2/c;;1-8(2,3)7-9(4,5)6/h;;(H2,1,2,3)(H2,4,5,6)/q2+1;/p-2 Key: GYQBBRRVRKFJRG-NUQVWONBAI
SMILES [Na+].[Na+].[O-]P(=O)(O)OP([O-])(=O)O
Properties
Chemical formula	Na₂H₂P₂O₇
Molar mass	221.94 g/mol
Appearance	White odorless powder
Density	2.31 g/cm³
Melting point	>600 °C
Solubility in water	11.9 g/100 mL (20 °C)
Refractive index (n_D)	1.4645 (hexahydrate)
Hazards
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD₅₀ (median dose)	2650 mg/kg (mouse, oral)
Related compounds
Other anions	Disodium phosphate Pentasodium triphosphate Sodium hexametaphosphate
Other cations	Calcium pyrophosphate Dipotassium pyrophosphate
Related compounds	Tetrasodium pyrophosphate
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

Disodium pyrophosphate or sodium acid pyrophosphate is an inorganic compound consisting of sodium cations and pyrophosphate anion. It is a white, water-soluble solid that serves as a buffering and chelating agent, with many applications in the food industry. When crystallised from water, it forms a hexahydrate, but it dehydrates above room temperature. Pyrophosphate is a polyvalent anion with a high affinity for polyvalent cations, e.g. Ca²⁺.

Disodium pyrophosphate is produced by heating sodium dihydrogen phosphate:

Disodium pyrophosphate is a popular leavening agent found in baking powders. It combines with sodium bicarbonate to release carbon dioxide:

It is available in a variety of grades that affect the speed of its action. Because the resulting phosphate residue has an off-taste, SAPP is usually used in very sweet cakes which mask the off-taste.

Disodium pyrophosphate and other sodium and potassium polyphosphates are widely used in food processing; in the E number scheme, they are collectively designated as E450, with the disodium form designated as E450(a). In the United States, it is classified as generally recognized as safe (GRAS) for food use. In canned seafood, it is used to maintain color and reduce purge during retorting. Retorting achieves microbial stability with heat. It is an acid source for reaction with baking soda to leaven baked goods. In baking powder, it is often labeled as food additive E450. In cured meats, it speeds the conversion of sodium nitrite to nitrite (NO₂⁻) by forming the nitrous acid (HONO) intermediate, and can improve water-holding capacity. Disodium pyrophosphate is also found in frozen hash browns and other potato products, where it is used to keep the color of the potatoes from darkening.

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Wikipedia