Hypophosphorous acid appears as colorless oily liquid or deliquescent crystals with a sour odor, it is a weak acid.

Lewis structure

Properties

Pure hypophosphorous acid forms white crystals that melt at 26.5 °C (79.7 °F). The electronic structure of hypophosphorous acid is such that it has only one hydrogen atom bound to oxygen, and it is thus a monoprotic oxyacid. It forms only one series of salts, the hypophosphites.

Preparation

Hypophosphorous acid is prepared industrially via a two step process:

Firstly, elemental white phosphorus reacts with alkali and alkaline earth hydroxides to give an aqueous solution of hypophosphites:

P4 + 4 OH^? + 4 H2O → 4 H2PO2^?+ 2 H2

Any phosphites produced in this step can be selectively precipitated out by treatment with calcium salts. The purified material is then treated with a strong, non-oxidizing acid (often sulfuric acid) to give the free hypophosphorous acid:

H2PO2^?+ H⁺ → H3PO2

Uses

Hypophosphorous acid is primarily used for electroless nickel plating. It is involved in the reduction of arenediazonium salts. It acts as an additive in Fischer esterification reactions. Also, it serves as a neutralizing agent, antioxidant, catalyst in polymerization and poly condensation, and wetting agent.

Hazard

Hypophosphorous acid is danger, it will cause severe skin burns and eye damage, it may cause respiratory irritation.

Prevention

Do not breathe dust/fume/gas/mist/vapors/spray

Wash face, hands and any exposed skin thoroughly after handling

Wear protective gloves/protective clothing/eye protection/face protection

Use only outdoors or in a well-ventilated area

Storage

Keep in a dry, cool and well-ventilated place. Keep container tightly closed. Corrosives area.

Incompatible materials: Strong oxidizing agents. Strong bases. Metals.