Disodium pyrophosphate
[CAS 7758-16-9]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Phosphides, metal phosphoric acid, metaphosphoric acid, hypophosphorous acid and pyrophosphate
• Name: Disodium pyrophosphate
• Synonyms: Disodium dihydrogenpyrophosphate; Diphosphoric acid disodium salt; Disodium dihydrogen pyrophosphate
• Molecular Formula: Na₂H₂P₂O₇
• Molecular Weight: 221.94
• CAS Registry Number: 7758-16-9
• EC Number: 231-835-0
• SMILES: OP(=O)([O-])OP(=O)(O)[O-].[Na+].[Na+]

Properties

• Melting point: 600 °C (Expl.)

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H302-H319
• Safety Statements: P264-P264+P265-P270-P280-P301+P317-P305+P351+P338-P330-P337+P317-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	4	H302
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Serious eye damage	Eye Dam.	1	H318

chemBlink Chemical Story

Disodium pyrophosphate, commonly called sodium acid pyrophosphate or SAPP, shows how a phosphate can be designed not merely to control pH but to control time. Its formula is Na₂H₂P₂O₇. Unlike ordinary orthophosphate, pyrophosphate contains two phosphorus centers joined through a P-O-P bridge. The compound is acidic enough in water to react with bicarbonate, and that reaction became the basis of one of its most familiar uses: chemical leavening.

In baking powder and prepared doughs, sodium bicarbonate releases carbon dioxide when neutralized by an acid. If all the gas appears too early, it can escape before the dough structure is ready to retain it; if it appears too late, expansion is incomplete. SAPP can be manufactured in grades with different reaction rates, and food-grade specifications even allow suitable calcium or aluminum salts to be present to control leavening behavior. The chemistry is therefore not simply acid plus bicarbonate. It is reaction-rate engineering synchronized with mixing, resting, heating, and starch/protein setting.

The same pyrophosphate structure gives SAPP another useful property: it can interact with metal ions and participate in sequestration and dispersion. Pyrophosphate is a condensed phosphate, and its multiple oxygen donor sites can coordinate cations. In foods this chemistry contributes to functions beyond leavening, including control of mineral interactions and processing behavior. But these applications depend on formulation; the name of the ingredient alone does not predict its exact performance.

Pyrophosphate also has a striking biochemical counterpart. In cells, pyrophosphate is generated when many biosynthetic reactions use ATP or related nucleotide triphosphates. Enzymatic hydrolysis of pyrophosphate to orthophosphate helps pull such reactions forward thermodynamically. The food ingredient and the cellular intermediate are not interchangeable biological concepts, but they share the same P-O-P motif and illustrate how much chemical potential can be associated with condensed phosphate bonds.

SAPP matters because it makes reaction timing visible in an everyday product. A biscuit rising in an oven is partly a kinetic experiment: carbon dioxide must be produced at the right rate while the food matrix is becoming able to trap it. Disodium pyrophosphate turns acid-base chemistry into a controllable clock, demonstrating that industrial formulation often depends not merely on whether a reaction occurs, but on precisely when it occurs.

References:
Food Chemicals Codex. Sodium Acid Pyrophosphate. DOI: 10.31003/FCC_F100536_06_01.
U.S. FDA. 21 CFR provisions and food-ingredient information for sodium acid pyrophosphate.
Harold FM. Bacteriological Reviews. 1966;30:772-794. Biochemical context of phosphate and pyrophosphate metabolism.

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