Tetrasodium pyrophosphate
[CAS 7722-88-5]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Phosphides, metal phosphoric acid, metaphosphoric acid, hypophosphorous acid and pyrophosphate
• Name: Tetrasodium pyrophosphate
• Synonyms: Diphosphoric acid tetrasodium salt; Pyrophosphoric acid tetrasodium salt; Sodium diphosphate
• Molecular Formula: Na₄P₂O₇
• Molecular Weight: 265.90
• CAS Registry Number: 7722-88-5
• EC Number: 231-767-1
• SMILES: [O-]P(=O)([O-])OP(=O)([O-])[O-].[Na+].[Na+].[Na+].[Na+]

Properties

• Density: 2.53 g/mL (25 °C) (Expl.)

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Risk Statements: H302-H315-H318-H319-H335
• Safety Statements: P261-P264-P264+P265-P270-P271-P280-P301+P317-P302+P352-P304+P340-P305+P351+P338-P305+P354+P338-P317-P319-P321-P330-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Serious eye damage	Eye Dam.	1	H318
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Acute toxicity	Acute Tox.	3	H301
Acute toxicity	Acute Tox.	4	H312

chemBlink Chemical Story

Tetrasodium pyrophosphate, Na₄P₂O₇, belongs to the condensed phosphates. Its defining structural feature is the P-O-P bridge joining two phosphate tetrahedra. That bond changes the chemistry substantially compared with ordinary orthophosphate: pyrophosphate can bind multivalent metal ions, disperse particles, modify protein-water interactions, and act as a sequestrant.

Pyrophosphate can be viewed formally as a product of phosphate condensation with loss of water. In biology, the reverse reaction is equally important. Pyrophosphate is released in many biosynthetic reactions, and enzymatic hydrolysis of PPi to orthophosphate can help pull those reactions forward. Industrial tetrasodium pyrophosphate uses the same anion for very different purposes, exploiting its charge and metal-binding behavior rather than its biochemical energy role.

In food technology, regulatory sources identify tetrasodium pyrophosphate as an emulsifier, sequestrant, pH-control agent, stabilizer, and related functional additive. Its ability to bind calcium and other metal ions can change texture, prevent unwanted mineral reactions, and influence protein behavior. In detergents and cleaning systems, sequestration of hardness ions historically helped surfactants work more effectively and prevented mineral deposition, although environmental concerns about phosphate loading changed the use of phosphorus-containing builders in many regions.

The fully neutralized tetrasodium salt is strongly different from acid pyrophosphate salts used as leavening acids. Sodium acid pyrophosphate still contains acidic protons and can react with bicarbonate to release carbon dioxide in baking. Tetrasodium pyrophosphate instead represents the more basic end of the neutralization series. Similar names can therefore hide very different acid-base behavior and different technological functions.

The chelation role also explains why pyrophosphate can influence dispersions. Multivalent cations often bridge negatively charged surfaces or promote aggregation; binding part of that metal-ion population can change particle-particle interactions. In food, mineral slurries, and cleaning systems this can alter viscosity, suspension stability, and deposition. Such effects are formulation-specific, so the same pyrophosphate that improves one system may cause undesirable mineral balance or environmental phosphorus loading in another. Functional additives work through equilibria, and those equilibria belong to the whole formulation rather than to one ingredient in isolation.

Tetrasodium pyrophosphate matters because a single P-O-P bond changes what phosphate can do. Condensation converts familiar orthophosphate into an anion with stronger sequestration and distinctive interfacial effects. The same pyrophosphate motif appears in food processing, cleaning, mineral chemistry, and cellular metabolism. It is a good example of how linking two common inorganic units can create a chemical species whose behavior is more than the sum of its parts.

References:

1. U.S. FDA. Sodium pyrophosphate / tetrasodium pyrophosphate, CAS 7722-88-5.

2. FAO/WHO JECFA. Tetrasodium pyrophosphate, INS 450(iii).

3. Biochemistry literature on pyrophosphate release and inorganic pyrophosphatase.

4. General condensed phosphate chemistry and sequestration literature.

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