Phosphorous acid is produced from PCl3 and H3PO3, which are dicarboxylic acids, slightly stronger than phosphoric acid. It has strong reducing properties and readily reduces metal ions, making it suitable for producing potassium phosphite, aluminum phosphite, and other organophosphorus compounds. Phosphorous acid is widely used abroad in plant disease and pest control and plant nutrition. Its salts, when used as fungicides, are highly effective in inhibiting oomycete pathogens affecting Solanum, Brassica, and other leafy vegetables.

I. Basic Information

English Name: Phosphorous acid

CAS Number: 13598-36-2

Molecular Formula: H3PO3

Molecular Weight: 82

Density: 1.65 g/cm3

UN Number: 2834

EC NO: 237-066-7

Hazard Code: 81502

Hazard Class: 8

Appearance: White crystals

Melting Point: 73.6℃

Boiling Point: 200℃ (decomposes)

Solubility: Easily soluble in water and alcohol; highly hygroscopic.

Density: 1.65 g/cm³

Hazardous Characteristics: Corrosive; decomposes upon heating to produce the particularly harmful gas H3P.

II. Product Specifications

Phosphorous acid≥99.0%

PO4≤0.1%

Cl≤0.005%

SO4≤0.0001%

Pb≤0.0002%

Fe≤0.001%

III. Mechanism of Action

The +3 valent phosphorus in phosphorous acid can be transported through both the xylem and phloem of crops, accelerating nutrient absorption and utilization. Regarding disease resistance, it is believed that +3 valent phosphorus can induce crops to produce resistance toxins and pathogenesis-related proteins (PR proteins), possibly relying on salicylic acid (SA) to activate defense mechanisms, enabling crops to develop sustained immunity against pathogens.

IV. Product Characteristics

1. Phosphorous acid is highly hygroscopic.

2. It has strong deliquescent properties.

3. It has a certain degree of corrosiveness.

4. It has bactericidal effects. Phosphorites have been proven to increase crop yield and improve disease resistance.

V. Production Process

The main production process for high-grade products in China is the PCl3 hydrolysis method. The specific process is as follows: Hydrolysis method: PCl3 is slowly hydrolyzed by adding water dropwise under stirring to produce phosphorous acid. After purification, cooling crystallization, and decolorization, the finished phosphorous acid product is obtained. Its reaction is PCl3 + 3H2O → H3PO3 + 3HCl. Hydrogen chloride generated during the production process is recovered and reused to produce hydrochloric acid.

VI. Contact and Storage Measures

1. Wear protective gloves/protective clothing/protective goggles/protective mask.

2. Thoroughly wash skin after handling.

3. Store only in the original container. Do not inhale dust or fumes.

4. Do not eat, drink, or smoke while using this product.

Phosphorous acid may corrode metals. Avoid direct skin contact, as it can irritate the skin. Especially avoid contact with eyes, as it can cause serious eye damage. It is used as a reducing agent in chemical reactions, and the actual reaction is relatively mild and highly controllable. Phosphorous acid is used as a raw material for the production of potassium phosphite, aluminum phosphite, potassium dihydrogen phosphite, and calcium hydrogen phosphite. It is also used in synthetic fibers, pesticide industries, etc.