Phosphinate
Phosphinates or hypophosphites are a class of phosphorus compounds conceptually based on the structure of hypophosphorous acid. IUPAC prefers the term phosphinate in all cases, however in practice hypophosphite is usually used to describe inorganic species (e.g. sodium hypophosphite), while phosphinate typically refers to organophosphorus species.
Hypophosphites
The hypophosphite ion is (H
2PO
2)−
. The salts are prepared by heating white phosphorus in warm aqueous alkali e.g. Ca(OH)2:
- P4 + 2 Ca(OH)2 + 4 H2O → 2 Ca(H2PO2)2 + 2 H2
Hypophosphites are reducing agents:
- (H
2PO
2)−
+ 3 OH− → (HPO
3)2−
+ 2 H2O + 2 e−
Hypophosphites are used in electroless nickel plating as the reducing agent to deposit for example Ni metal from Ni salts. The hypophosphite ion is thermodynamically unstable, and disproportionates on heating to phosphine and phosphate salts:
- 2 H
2PO
2−
→ PH3 + HPO
42−
Uses
Hypophosphite (usually sodium hypophosphite) acts as a reducing agent to deposit nickel onto surfaces without using electricity. Common in electronics, automotive, and aerospace industries for corrosion resistance and hardness. Some hypophosphite compounds are used in medicines, particularly as sources of phosphorus or as stabilizers in formulations.
In polymer and plastic stabilization, they are used today as antioxidants and thermal stabilizers to prevent degradation during the processing of plastics like PVC. Beyond nickel plating, hypophosphites are used in general chemical synthesis where a mild reducing agent is needed.
Additionally, in wood science, sodium hypophosphite in combination with other agents, such as ammonium-, nitrogen- or aluminium-containing chemicals, has been used for in solid wood and particleboard to improve the fire retarding properties.
See also
- Organophosphinic acid
- Phosphine - PR3
- Phosphine oxide - OPR3
- Phosphite - P(OR)3
- Phosphonate - OP(OR)2R
- Phosphate - OP(OR)3