Sodium tripolyphosphate
[CAS# 7758-29-4]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Phosphides, metal phosphoric acid, metaphosphoric acid, hypophosphorous acid and pyrophosphate
• Name: Sodium tripolyphosphate
• Synonyms: Pentasodium triphosphate; Sodium triphosphate; STPP
• Molecular Formula: Na₅P₃O₁₀
• Molecular Weight: 367.86
• CAS Registry Number: 7758-29-4
• EC Number: 231-838-7
• SMILES: [O-]P(=O)([O-])OP(=O)([O-])OP(=O)([O-])[O-].[Na+].[Na+].[Na+].[Na+].[Na+]

Properties

• Water solubility: 20 g/100 mL (20 °C)
• Melting point: 622 °C

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H319-H335
• Safety Statements: P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

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

Discovery and Applications

Sodium tripolyphosphate (STPP), with the chemical formula Na₅P₃O₁₀, was synthesized in the early 20th century as chemists sought to develop effective detergents. Sodium tripolyphosphate is formed by the condensation of phosphoric acid (H₃PO₄) with sodium hydroxide (NaOH) to form a polyphosphate chain structure. The resulting compound consists of five sodium ions (Na⁺) attached to a linear triphosphate chain (P₃O₁₀⁵⁻).

The main applications of sodium tripolyphosphate are in detergents and cleaning products. It acts as a water softener, preventing the precipitation of hardness ions such as calcium and magnesium in water. This property enhances the effectiveness of detergents by improving their ability to bind to dirt and soil, resulting in cleaner, brighter clothes. In addition to household detergents, STPP is also used in industrial cleaning, including metal finishing, boiler cleaning, and vehicle washing. Its chelating properties help prevent scaling and increase the efficiency of the cleaning process. In textile manufacturing, sodium tripolyphosphate is used as a dispersant and leveling agent for dyes. It ensures uniform dye absorption by textile fibers, improves color uniformity and reduces dye wastage. In addition, it helps prevent redeposition of dirt and impurities on fabrics during washing. STPP is used as a dispersant in ceramic and clay processing. It helps control viscosity, improves plasticity, and enhances the uniformity of ceramic slurries and clay suspensions during molding and firing.

In the food industry, sodium tripolyphosphate is primarily used as a food additive (E451) due to its water-retaining and emulsifying properties. It improves moisture retention and texture in processed meat, seafood, and poultry products. In addition, it stabilizes and improves the appearance of canned and frozen foods. STPP is used as a corrosion inhibitor and antiscalant in water treatment facilities. It helps control water hardness and prevents scale buildup in pipes and equipment, thereby extending their service life and improving overall efficiency.

References

2007. Electrosprayed bovine serum albumin-loaded tripolyphosphate cross-linked chitosan capsules: Synthesis and characterization. Journal of Microencapsulation.
DOI: 10.1080/02652040601058434

2010. Chitosan/Polyethylene Glycol Beads Crosslinked with Tripolyphosphate and Glutaraldehyde for Gastrointestinal Drug Delivery. AAPS PharmSciTech.
DOI: 10.1208/s12249-010-9483-z

2019. Tripolyphosphate-assisted electro-Fenton process for coking wastewater treatment at neutral pH. Environmental science and pollution research international, 26(8).
DOI: 10.1007/s11356-019-04548-w