Disodium pyrophosphate
Disodium pyrophosphate, also known as sodium acid pyrophosphate (SAPP), is an inorganic compound with the chemical formula Na₂H₂P₂O₇ and a molecular weight of 221.94 g/mol.[1] It appears as a white, odorless crystalline powder or granules that is highly soluble in water, with a pH of approximately 4 in a 1% solution, and decomposes at around 220°C.[2] This sodium salt of pyrophosphoric acid is produced industrially by neutralizing phosphoric acid with sodium hydroxide or carbonate followed by thermal dehydration at about 250°C.[2] In the food industry, disodium pyrophosphate serves multiple functions as a generally recognized as safe (GRAS) additive, including acting as a leavening agent in baked goods like cakes and pancakes by releasing carbon dioxide upon reaction with baking soda.[1] It also functions as an emulsifier in processed cheeses to prevent separation and as a sequestrant in canned tuna or potatoes to inhibit discoloration and chelate metal ions that could affect quality.[2] Beyond food, it finds applications in industrial processes such as electroplating, metal cleaning, and as a dispersant in oil well drilling muds, as well as in cosmetics as a chelating and buffering agent.[1] Disodium pyrophosphate is regulated as GRAS by the U.S. Food and Drug Administration (FDA) for use in human food and animal feeds under good manufacturing practices, with specific limits in standardized foods such as up to 3% in cheese products and 0.5% in canned tuna.[2] The U.S. Environmental Protection Agency (EPA) exempts it from pesticide residue tolerances when used as an inert ingredient, and it is approved internationally by bodies like Codex Alimentarius (INS 450(i)) and the European Union (E 450(i)), with a recommended phosphorus intake limit of 70 mg/kg body weight per day.[2] Safety assessments indicate low toxicity, with an oral LD50 of 2650 mg/kg in mice, though it can cause mild irritation to skin, eyes, and respiratory tract upon direct exposure to dust.[1]Chemical identity and properties
Nomenclature and identifiers
Disodium pyrophosphate is systematically named disodium dihydrogen diphosphate according to IUPAC nomenclature.[1] It is commonly referred to as sodium acid pyrophosphate (SAPP) or disodium diphosphate in industrial and food contexts.[1][3] Key chemical identifiers for disodium pyrophosphate include the following:| Identifier | Value |
|---|---|
| CAS Number | 7758-16-9[1] |
| EC Number | 231-835-0 |
| E Number (food additive) | E450(i)[3] |