Overview
Hypophosphorous acid (CAS 6303-21-5 ), also known as phosphinic acid and commonly abbreviated as HPA, is a reducing acid used across chemical manufacturing, surface treatment, and stabilization processes.
It functions primarily as a strong reducing agent and antioxidant, preventing oxidative degradation in sensitive formulations and enabling metal deposition in industrial finishing applications.
In electroless nickel plating, HPA serves as the reducing agent that drives metal deposition onto non-conductive substrates, making it a process-critical input for electronics and precision component manufacturing.
Pharmaceutical manufacturers use it to prevent discoloration and oxidative breakdown in active ingredient formulations during production and storage. It ensures the stability of sensitive chemical compounds.
In textile and leather processing, it controls unwanted oxidation during dyeing and finishing operations, improving color consistency and product shelf life for high-quality consumer goods.
Water treatment applications rely on HPA for pH regulation and as a reducing agent to manage dissolved oxygen and metal ion activity in complex industrial process water systems.
Hypophosphorous acid is supplied as an aqueous solution, with 50% concentration being the most commercially standard grade. Technical and industrial grades are the primary market offerings for most users.
Pharmaceutical-grade material is available to meet stricter purity requirements for drug manufacturing applications. Bulk liquid supply in IBC containers and drums is the typical packaging format for buyers.
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Physical Properties
| Melting Point | 26.5 °C |
| Boiling Point | 108 °C (759.8513 mmHg) |
| Density | 1.479 g/cm³ @ Temp: 20 °C |
| Appearance | colourless liquid |
| Color | Colorless |
| Form | hygroscopic crystals or colorless oily liquid |
| Water Solubility | SOLUBLE |
| Vapor Pressure | <17 mmHg ( 20 °C) |
| pH | pKa1= 1.00(25℃) |
Safety & Handling
Danger GHS05 Hazard Statements H290 May be corrosive to metals H314 Causes severe skin burns and eye damage H318 Causes serious eye damage Precautionary Statements P234 Keep only in original packaging. P260 Do not breathe dust/fume/gas/mist/vapours/spray. P264 Wash … thoroughly after handling. P280 Wear protective gloves/protective clothing/eye protection/face protection. P316 Get emergency medical help immediately. P317 Get emergency medical help. P321 Specific treatment (see … on this label). P363 Wash contaminated clothing before reuse. P390 Absorb spillage to prevent material damage. P405 Store locked up. P406 Store in a corrosion-resistant/… container with a resistant inner liner. P501 Dispose of contents/container in accordance with local regulations. P264+P265 Wash … thoroughly after handling. P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing. P301+P330+P331 Rinse mouth. Do NOT induce vomiting. P302+P361+P354 IF ON SKIN: Take off immediately all contaminated clothing. Rinse skin with water/shower. P305+P354+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
Trade & Regulatory
| HS Code | 28111990 |
| UN Number | 3264 |
| ADR Class | 8 |
| Packing Group | III |
| Storage Class | 8B - Non-combustible corrosive hazardous materials |
| WGK (Germany) | 1 |
Other Names
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Chemical Properties
- CAS Number
- 6303-21-5
- EC Number
- 228-601-5
- Mol. Weight
- 65.996
- HS Code
- 28111990
- Category
- Oxidizers & Peroxides