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.

## Contents

* 1 Hypophosphites
* 2 Uses
* 3 See also
* 4 References

## Hypophosphites

The hypophosphite ion is (H2PO2)−. The salts are prepared by heating white phosphorus in warm aqueous alkali e.g. Ca(OH)2:[1]

P4 \+ 2 Ca(OH)2 \+ 4 H2O → 2 Ca(H2PO2)2 \+ 2 H2

Hypophosphites are reducing agents:[1]

(H2PO2)− \+ 3 OH− → (HPO3)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.[1] The hypophosphite ion is thermodynamically unstable, and disproportionates on heating to phosphine and phosphate salts:

2 H2PO2− → PH3 \+ HPO42−

## 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.[2][3]

## See also

* Organophosphinic acid
* Phosphine \- PR3
* Phosphine oxide \- OPR3
* Phosphite - P(OR)3
* Phosphonate \- OP(OR)2R
* Phosphate \- OP(OR)3

## References

1. ↑ 1.0 1.1 1.2 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 512. ISBN 978-0-08-037941-8.
2. ↑ Pan, Fangya; Jia, Hongyu; Huang, Yuxiang; Chen, Zhilin; Liang, Shanqing; Jiang, Peng (2023-11-21). "Analyzing Temperature Distribution Patterns on the Facing and Backside Surface: Investigating Combustion Performance of Flame-Retardant Particle Boards Using Aluminum Hypophosphite, Intumescent, and Magnesium Hydroxide Flame Retardants". Polymers (MDPI AG) 15 (23): 4479. doi:10.3390/polym15234479. ISSN 2073-4360.
3. ↑ Kim, Injeong; Ross, Lone; Alfredsen, Gry; Karlsson, Olov; Kaynak, Elif; Das, Oisik; Jones, Dennis; Mantanis, George I. et al. (2025-03-16). "Enhancement of Biological Durability and Fire Safety in Wood Modified with Maleic Anhydride and Sodium Hypophosphite". Forests (MDPI AG) 16 (3): 526. doi:10.3390/f16030526. ISSN 1999-4907.

* v
* t
* e

Organophosphorus

Only P-O bonds|

| P(III)|

* Phosphite/Organophosphite

|

P(V)|

* Phosphate/Organophosphate

With P-C bonds|

| One P-C bonds|

| P(III)|

* Phosphonite

|

P(V)|

* Phosphonate

Two P-C bonds|

| P(III)|

* Phosphinite

|

P(V)|

* Phosphinate

Three P-C bonds|

| P(III)|

* Phosphine

|

P(V)|

* Phosphine oxide

With P-N bonds|

| One P-N bond|

| P(III)|

* Phosphoramidite
* e.g. Nucleoside phosphoramidite

|

P(V)|

* Phosphoramidate
* e.g. Phosphocreatine

Two P-N bond|

| P(III)|

* Phosphorodiamidite

|

P(V)|

* Phosphorodiamidate
* e.g. Morpholino
* Cyclophosphamide

Three P-N bond|

| P(V)|

* Phosphoramide
* e.g. Hexamethylphosphoramide
* Metepa

|

With P-C and P-N bonds|

| One P-C bond and one P-N bond|

| P(V)|

* Phosphonamidate

|

One P-C bond and two P-N bond|

| P(V)|

* Phosphonamide

|

Two P-C bond and one P-N bond|

| P(V)|

* Phosphinamide

|

With P-S bonds|

| One P-S bond|

| P(III)|

* Phosphorothioite

|

P(V)|

* Phosphorothioate

Two P-S bond|

| P(III)|

* Phosphorodithioite

|

P(V)|

* Phosphorodithioate

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