Phosphorous Acid (Phosphonic Acid, H₃PO₃)
Phosphorous acid (phosphonic acid, H₃PO₃) is a high-purity (99%), white, crystalline and odorless compound used in both agricultural and industrial applications. In agriculture it is an active ingredient in SL fungicide formulations and special liquid plant nutrition products. In industry it works as a reducing agent, stabilizer and intermediate in many chemical processes.
Chemical Formula: H₃PO₃
CAS No: 13598-36-2
Density: 1.651 g/cm³
Melting Point: 73.6 °C
Boiling Point: 200 °C
Water Solubility: 310 g/100 ml (20 °C)
What Is Phosphorous Acid?
Phosphorous acid is an inorganic acid with the formula H₃PO₃ that dissolves readily in water. It is also sold as phosphonic acid or orthophosphorous acid. All three names refer to the same compound (CAS 13598-36-2).
It is often confused with phosphoric acid (H₃PO₄), although the two are different compounds. Phosphoric acid is a direct phosphorus source in fertilizer production, while phosphorous acid forms mobile phosphite ions in the plant and is valued mainly for its fungicidal effect. Data on the other compound is available on our phosphoric acid page.
Chemical and Physical Properties
Phosphorous acid is produced by controlled hydrolysis of phosphorus trichloride or by other synthesis routes. It is a moderately strong acid and a strong reducing agent. The compound is hygroscopic and absorbs moisture from the air. On strong heating it decomposes and can release phosphine, so handling requires proper safety measures. Detailed physicochemical data is available in the PubChem database.
| Property | Value |
|---|---|
| Appearance | White crystal, odorless |
| CAS No | 13598-36-2 |
| Molecular Formula | H₃PO₃ |
| Chemical Name | Orthophosphorous Acid, Phosphonic Acid |
| Purity | 99% |
| Density | 1.651 g/cm³ |
| Melting Point | 73.6 °C |
| Boiling Point | 200 °C |
| Solubility in Water | 310 g/100 ml (20 °C) |
| Other Solubility | Soluble in ethanol and alcohols |
| Storage Condition | Store in a cool, dry and well-ventilated place, away from moisture and heat, in sealed packaging. |
Usage Areas
Plant Nutrition and Protection Products
Phosphorous acid is used mainly in SL fungicide formulations and special liquid fertilizers. It enhances plant resistance and nutrient absorption efficiency.
- Used in liquid SL fungicide formulations
- Acts as a phosphorus source in plant nutrition
- Improves product efficiency in custom liquid formulations
Research has shown that phosphite salts derived from phosphorous acid have a systemic fungicidal effect against oomycete diseases such as Phytophthora and Pythium. For details see the University of Florida (EDIS) publication and the Pacific Northwest Pest Management Handbooks. Phosphites are widely used in orchards, vineyards and vegetable production.
Potassium Phosphite Production
The most common use in the liquid fertilizer sector is the production of potassium phosphite. Phosphorous acid is neutralized with potassium hydroxide to obtain a potassium phosphite solution.
Industrial Applications
This compound serves several functions across industries:
- Used in reduction reactions as a chemical agent
- Precursor in phosphonate synthesis for water treatment
- Acts as a stabilizer in PVC manufacturing
- Used in the production of synthetic fibers, emulsifiers, flotation agents and viscosity adjusters
Among other raw materials for fungicide production, Obafer Kimya also supplies copper chloride dihydrate.
Is Phosphorous Acid Hazardous?
Used correctly and at the right dosage, it is considered safe. Direct skin contact may cause irritation, eye contact may cause serious irritation, and inhaling the dust may irritate the respiratory tract. Protective gloves, goggles and a mask should be worn during handling, and workplace safety instructions should be followed.
Storage and Transport
Store in a dry, cool place, away from moisture and direct sunlight, in airtight packaging made of chemically resistant material. Under proper conditions the product keeps its properties for a long time.
Frequently Asked Questions
What is phosphorous acid used for?
It is the main raw material for systemic fungicides and phosphite-based plant nutrition products. It stimulates the plant’s natural defense mechanisms and protects against oomycete diseases such as Phytophthora and Pythium. In industry it is used as a reducing agent, stabilizer and intermediate.
What is the difference between phosphorous acid and phosphoric acid?
Phosphorous acid (H₃PO₃) and phosphoric acid (H₃PO₄) are different compounds. Phosphoric acid is a direct phosphorus source in fertilizer production, while phosphorous acid forms phosphite ions that move within plant tissue and stands out for its fungicidal effect.
Are phosphonic acid and phosphorous acid the same?
Yes. Phosphonic acid and phosphorous acid are two names for the same compound (H₃PO₃, CAS 13598-36-2), and both are common in the industry.
How is phosphorous acid packaged?
Obafer Kimya supplies 99% phosphorous acid in crystalline form, in bulk and in packaging suitable for industrial use. Contact us for packaging options and supply terms.
Reliable Supply with Obafer Quality
When buying phosphorous acid, purity, certificates of analysis and supplier reliability matter. Obafer Kimya supplies high-purity phosphorous acid at wholesale for agricultural and industrial formulations, with technical support. Contact us for details.
