Phosphorous Acid
Phosphorous acid is an important inorganic oxoacid of phosphorus and is a key intermediate in both industrial chemistry and agricultural formulations.
CAS # 13598-36-2
Phosphorous acid is readily soluble in water and has many polar solvents, forming acidic solutions with strong reducing capability. Because of this behavior, phosphorous acid is widely used in redox chemistry, specialty synthesis reactions, and the manufacture of valuable phosphorus-containing derivatives.
Phosphorous acid plays a significant industrial role due to its distinct chemical behavior and ability to form phosphite salts. These derivatives have unique physical, agricultural, and industrial properties that are highly valuable in manufacturing sectors.
General Information and Properties
Other names: Phosphonic acid
Chemical formula: H₃PO₃
Appearance: White, crystalline, hygroscopic solid
Melting point: ~73–74 °C (decomposes slowly on heating)
Applications
Manufacture of Phosphite Salts and Derivatives
One of the most prominent uses of phosphorous acid is the production of phosphite salts, including: Sodium phosphite, Potassium phosphite, and Calcium phosphite.
Agriculture and Plant Health
Phosphorous acid’s phosphite derivatives are widely used in modern crop management strategies. Phosphites are valued for providing rapid plant uptake and translocation, enhancing natural plant defense responses, and acting as active components in fungicide formulations.
Reducing Agent in Chemical Synthesis
Phosphorous acid functions as a selective reducing agent, making it valuable in reduction of metal ions in controlled environments, synthesis of specialty organophosphorus intermediates, and industrial redox reactions.
Plastics, Polymers, and Materials Processing
Phosphorous acid is used indirectly in the production of phosphite stabilizers, which serve as antioxidants for plastics and heat stabilizers to reduce polymer degradation during processing.
Water Treatment and Industrial Chemical Formulations
Due to their stability and performance, phosphite derivatives are used in corrosion and scale inhibitors, boiler-water treatment chemicals, and industrial cleaning agents.
Advantages
Efficient Reducing Agent: It provides reliable, controlled reduction in synthesis without the unpredictability associated with some stronger reducing agents.
Versatile Precursor: Forms a wide variety of phosphite salts, many of which have applications that phosphorous acid alone cannot provide.
High Solubility: Dissolves readily in water and polar solvents, allowing easy incorporation into liquid formulations.
Compatibility with Industrial Materials: Useful in polymer stabilization, agricultural formulations, metal surface treatments, and specialty chemical manufacturing.
Safety and Handling Information
While phosphorous acid is widely used, it is classified as a corrosive and potentially hazardous chemical, and appropriate precautions must be taken.
Corrosive to skin and eyes: Can cause burns or severe irritation.
Respiratory hazard: Dust or mist may irritate the throat and lungs.
Harmful if swallowed: May cause gastrointestinal distress or corrosive injury.
Thermal decomposition: Produces irritating phosphorus oxides.