Phosphinates or hypophosphites are a class of
phosphorus
Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...
compounds conceptually based on the structure of
hypophosphorous acid
Hypophosphorous acid (HPA), or phosphinic acid, is a phosphorus oxyacid and a powerful reducing agent with molecular formula H3PO2. It is a colorless low-melting compound, which is soluble in water, dioxane
and alcohols. The formula for th ...
.
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
prefers the term phosphinate in all cases, however in practice hypophosphite is usually used to describe inorganic species (e.g.
sodium hypophosphite
Sodium hypophosphite (NaPO2H2, also known as sodium phosphinate) is the sodium salt of hypophosphorous acid and is often encountered as the monohydrate, NaPO2H2·H2O. It is a solid at room temperature, appearing as odorless white crystals. It is s ...
), while phosphinate typically refers to
organophosphorus
Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarb ...
species.
Hypophosphites
The hypophosphite
ion
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
is . The salts are prepared by heating white phosphorus in warm aqueous alkali e.g. Ca(OH)
2:
:P
4 + 2 Ca(OH)
2 + 4 H
2O → 2 Ca(H
2PO
2)
2 + 2 H
2
Hypophosphites are
reducing agents
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ).
Examples of substances that are common reducing agents include hydrogen, carbon ...
:
: + 3 OH
− → + 2 H
2O + 2 e
−
Hypophosphites are used in
electroless nickel plating
Electroless Deposition, Electroless nickel-phosphorus plating, also referred to as ''E-nickel'', is a chemical engineering, chemical process that deposits an even layer of nickel-phosphorus alloy on the surface of a solid substrate, like metal o ...
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
Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...
and
phosphate
Phosphates are the naturally occurring form of the element phosphorus.
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...
salt
In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...
s:
: 2 → PH
3 +
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
Wood science is the scientific field which predominantly studies and investigates elements associated with the formation, the physical and chemical composition, and the macro- and microstructure of wood as a bio-based and lignocellulosic materi ...
, 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
An organophosphinic acid is an organophosphorus compound with the formula R2−nHnPO2H (R = alkyl, aryl). One or both P-H bonds in the parent hypophosphorous acid (aka phosphinic acid) are replaced by organic groups. The Cyanex family of dialk ...
*
Phosphine
Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...
- PR
3
*
Phosphine oxide
Phosphine oxide is the inorganic compound with the formula H3PO. Although stable as a dilute gas, liquid or solid samples are unstable. Unlike many other compounds of the type POxHy, H3PO is rarely discussed and is not even mentioned in major so ...
- OPR
3
*
Phosphite
The general structure of a phosphite ester showing the lone pairs on the P
In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of ...
- P(OR)
3
*
Phosphonate
In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing Functional group, groups, where R is an organic group (alkyl, aryl). If R is hydrogen then the compound is a Phosphite_ester#Chemistry_of_HP(O)(OR ...
- OP(OR)
2R
*
Phosphate
Phosphates are the naturally occurring form of the element phosphorus.
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...
- OP(OR)
3
References
{{Organophosphorus
Functional groups