Disodium 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 Registry Number	7758-16-9 Y
ChemSpider	22859 N
EC number	231-835-0
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
Jmol-3D images	Image
PubChem	24451
SMILES [Na+].[Na+].[O-]P(=O)(O)OP([O-])(=O)O
UNII	H5WVD9LZUD Y
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 (nD)	1.4645 (hexahydrate)
Hazards
EU Index	Not listed
Flash point	Non-flammable
LD50 (Median lethal 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 noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
N verify (what is: Y/N?)
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:

2 NaH₂PO₄ → Na₂H₂P₂O₇ + H₂O

Food uses

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

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.^[1]

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 during retorting. Retorting achieves microbial stability with heat.^[2] It is an acid source for reaction with baking soda to leaven baked goods.^[3] In baking powder, it is often labeled as food additive E450.^[4] 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.^[3]

Other uses

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.

References

1. ↑ 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
2. ↑ -Retorting, Accessed 2010-11-27
3. ↑ 3.0 3.1 Ellinger, R.H. (1972). "Phosphates in Food Processing". Handbook of Food Additives (2nd ed.). Cleveland: CRC Press. pp. 617–780. 
4. ↑