Disodium dihydrogen diphosphate
Diphosphoric acid, disodium salt
Disodium dihydrogen pyrophosphate
Sodium acid pyrophosphate, SAPP
|Molar mass||221.94 g/mol|
|Appearance||White odorless powder|
|Melting point||>600 °C|
|11.9 g/100 mL (20 °C)|
Refractive index (nD)
|EU Index||Not listed|
LD50 (Median lethal dose)
|2650 mg/kg (mouse, oral)|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
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:
- 2 NaH2PO4 → Na2H2P2O7 + H2O
- Na2H2P2O7 + NaHCO3 → Na3HP2O7 + CO2 + H2O
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.
It is designated in the United States as generally recognized as safe (GRAS) for food use. It is used in canned seafood to maintain color and reduce purge[clarification needed] 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,[clarification needed] 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.
In leather treatment, it can be used to remove iron stains on hides during processing. It can stabilize hydrogen peroxide solutions against reduction. It can be used with sulfamic acid in some dairy applications for cleaning, especially to remove soapstone. When added to scalding water, it facilitates removal of hair and scurf in hog slaughter and feathers and scurf in poultry slaughter. In petroleum production, it can be used as a dispersant in oil well drilling muds.
- John Brodie, John Godber "Bakery Processes, Chemical Leavening Agents" in Kirk-Othmer Encyclopedia of Chemical Technology 2001, John Wiley & Sons. doi:10.1002/0471238961.0308051303082114.a01.pub2
-  -Retorting, Accessed 2010-11-27
- Ellinger, R.H. (1972). "Phosphates in Food Processing". Handbook of Food Additives (2nd ed.). Cleveland: CRC Press. pp. 617–780.