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Phosphorous Acid
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Description
Phosphorous Acid
Other Names: Orthophosphorous acid, Dihydroxyphosphine oxide
CAS Number: 13598-36-2
Sum Formula: H₃PO₃
Molar Mass: 82.00 g/mol
Appearance: White crystalline solid or powder
Phosphorous acid is a diprotic, inorganic oxyacid of phosphorus. It contains one P=O bond and two hydroxyl groups, making it a moderately strong reducing agent and a versatile intermediate in chemical synthesis. It is widely used in corrosion inhibition, metal treatment, and the manufacture of phosphonates and organophosphorus compounds.
Chemical and Physical Properties
Density: ~1.65 g/cm³
Melting Point: 73–74°C (decomposes on heating)
Boiling Point: Decomposes before boiling
Solubility in Water: Highly soluble
Solubility in Organic Solvents: Slightly soluble in alcohols
pKa: ~1.3 (first dissociation), ~6.7 (second)
Odor: Odorless
Stability: Stable under dry conditions; decomposes in hot aqueous solution
Applications
Used as a reducing agent in chemical synthesis
Intermediate in the production of phosphonates and phosphinates
Applied in corrosion inhibitors and metal surface treatments
Used in technical formulations requiring phosphorus-based acids
Employed in polymer chemistry and specialty reagent systems
Safety
Signal Word: Warning
H302: Harmful if swallowed [Warning Acute toxicity, oral]
H314: Causes severe skin burns and eye damage [Danger Skin corrosion/irritation]
P260, P264, P270, P280, P301+P317, P301+P330+P331, P302+P361+P354, P304+P340, P305+P354+P338, P316, P321, P330, P363, P405, and P501
First Aid Measures
Eye Contact: Rinse immediately with water for several minutes. Seek medical attention if irritation persists
Skin Contact: Wash with plenty of soap and water. Remove contaminated clothing
Inhalation: Move to fresh air. Seek medical help if respiratory symptoms appear
Ingestion: Rinse mouth. Do not induce vomiting. Seek medical advice
Handling and Storage
Store in tightly closed containers in a cool, dry, and well-ventilated area
Keep away from strong bases, oxidizers, and moisture
Avoid generating dust. Use proper PPE to prevent contact with skin, eyes, and clothing