Hypophosphorous acid CAS 6303-21-5

Molecular Formula: HO2P
Molecular Weight: 63.980501
Appearance: colorless liquid
Purity: ≥95%
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Chemical substances play a pivotal role in modern society, contributing to a wide range of industries and applications. One such compound, Hypophosphorous acid(HPA), with the chemical formula H3PO2 and CAS number 6303-21-5, has garnered significant attention due to its diverse properties and applications. In this blog post, we will delve into the world of Hypophosphorous acid(HPA), exploring its properties, applications, and the significant role of HPA plays in our daily lives.

What Is Hypophosphorous Acid?

Hypophosphorous acid is a colorless oil or deliquescence crystal with low melting, also known as “hypophosphite”, ng, soluble in water, dioxane, and alcohols. As an important fine chemical product, its main use is as a reducing agent for electroless plating, phosphoric prevents the discoloration of resins. It can also be used in the esterification reaction catalyst, the refrigerant, in particular for the production of high-purity product sodium hypophosphite.

Hypophosphorous acid is a powerful reducing agent. The formula is generally written H3PO2, but a more descriptive presentation is HOP(O)H2 which highlights its monoprotic character. Salts derived from this acid are called phosphinates (hypophosphites). HOP(O)H2 exists in equilibrium with the minor tautomer HP(OH)2. In some cases, the minor tautomer is called hypophosphorous acid and the major tautomer is called phosphinic acid.

Properties of Hypophosphorous Acid

1. Reducing Agent

One of the most remarkable properties of Hypophosphorous acid(HPA) is its potent reducing capabilities. It effectively reduces metal ions like copper, silver, and nickel to their respective lower oxidation states. The reducing properties of HPA make it a key component in various chemical processes, such as electroless plating and metal refining. In electroless plating, the reduction of metal ions on the surface of substrates leads to uniform and high-quality metal coatings, which find applications in industries like electronics, automotive, and aerospace.

2Stabilizing Agent

Hypophosphorous acid(HPA) plays a crucial role as a stabilizing agent in certain chemical reactions. Its ability to scavenge free radicals and prevent unwanted side reactions makes it highly valuable in the pharmaceutical and chemical industries. For instance, during the synthesis of certain active pharmaceutical ingredients (APIs), the presence of HPA can enhance the yield and purity of the desired product by inhibiting undesirable byproducts.

3. Water Treatment

Due to its ability to remove dissolved oxygen from water, Hypophosphorous acid(HPA) finds extensive use in water treatment processes, particularly in boiler systems. Oxygen in boiler feedwater can lead to corrosion of metal components, reducing the efficiency and lifespan of industrial equipment. By reducing the oxygen content in water, HPA minimizes the risk of corrosion, ensuring smoother operation and longer equipment life.

4. Polymer Industry

In the polymer industry, Hypophosphorous acid(HPA) is employed as a chain transfer agent during the production of acrylic polymers and polyesters. This unique property allows manufacturers to control the molecular weight of polymers, leading to the synthesis of materials with desired physical and mechanical properties. Additionally, HPA acts as a stabilizing agent during the polymerization process, preventing unwanted side reactions and ensuring the production of high-quality polymers.

What Is Hypophosphorous Acid Used for?

1. Electroless Plating

As mentioned earlier, Hypophosphorous acid(HPA) is a key component in electroless plating processes. Electroless plating is an essential technique in various industries, providing a method for depositing a uniform layer of metal on different substrates without the need for an external power source. This process is widely used in the electronics industry to manufacture printed circuit boards (PCBs) and semiconductor devices. The deposition of thin metal layers on these substrates enhances electrical conductivity, corrosion resistance, and solderability.

2. Pharmaceuticals

The pharmaceutical industry relies on Hypophosphorous acid(HPA) for its role as a stabilizing agent in the synthesis of certain active pharmaceutical ingredients (APIs). The production of pharmaceuticals often involves complex chemical reactions, where the control of reaction conditions is critical to achieving high yields of the desired products. HPA‘s stabilizing properties help prevent side reactions, ensuring that the synthesis proceeds smoothly, resulting in the production of high-quality drugs.

3. Chemical Synthesis

Hypophosphorous acid(HPA) plays a pivotal role in the manufacture of various chemicals, including plasticizers, flame retardants, and antioxidants. Its reducing properties and compatibility with other compounds make it a preferred choice in several synthesis processes. For example, in the production of flame retardants, HPA serves as a reducing agent, enabling the conversion of metal compounds into flame-retardant additives used in various materials.

4. Agriculture

Hypophosphorous acid(HPA) is used in agricultural applications as a source of phosphorous. Phosphorous is an essential nutrient for plants, promoting healthy growth and improved crop yields. HPA‘s water-soluble nature allows it to be easily absorbed by plants, ensuring efficient nutrient uptake.

Safety Considerations

While Hypophosphorous acid(HPA) offers numerous benefits, it is essential to handle it with care. It is a corrosive compound and can cause severe skin and eye irritation. Also as a reducing agent, it can be reactive and may pose risks when mishandled. Proper personal protective equipment (PPE) should be worn while handling HPA, and all safety guidelines must be strictly adhered to. Storage of HPA should be in a cool, well-ventilated area away from incompatible substances.


CAS 6303-21-5Hypophosphorous Acid (CAS 6303-21-5) is a versatile chemical compound with significant applications in various industries. From its role as a reducing agent in chemical reactions to its application in electroless plating, water treatment, pharmaceuticals and agriculture, this compound’s diverse properties make it indispensable in modern manufacturing and technology. As researchers continue to explore new applications and methods of production, Hypophosphorous Acid‘s prominence in the chemical landscape is likely to remain steadfast, shaping the course of numerous industries for years to come.


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