Phosphinous acids are usually

organophosphorus compound 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 hydrocarbo ...

s with the formula R₂POH. They are pyramidal in structure. Phosphorus is in the oxidation state III. Most phosphinous acids rapidly convert to the corresponding phosphine oxide, which is tetrahedral and is assigned oxidation state V.

Synthesis

Only one example is known, bis(trifluoromethyl)phosphinous acid, (CF₃)₂POH. It is prepared in several steps from

phosphorus trichloride Phosphorus trichloride is an inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic ...

(Et = ethyl): :PCl₃ + 2 Et₂NH → PCl₂NEt₂ + Et₂NH₂Cl :2 P(NEt₂)₃ + PCl₂NEt₂ + 2 CF₃Br → P(CF₃)₂NEt₂ + 2 BrClP(NEt₂)₃ :P(CF₃)₂NEt₂ + H₂O → P(CF₃)₂OH + HNEt₂ WAJJOH

Reactions

With the lone exception of the bis(trifluoromethyl) derivative, the dominant reaction of phosphinous acids is

tautomerization In chemistry, tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the reloca ...

: :PR₂OH → OPR₂H Even the pentafluorophenyl compound P(C₆F₅)₂OH is unstable with respect to the

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 ...

. Although phosphinous acids are rare, their P-bonded

coordination complex A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

es are well established, e.g. Mo(CO)₅P(OH)₃.

Secondary and primary phosphine oxides

Tertiary phosphine oxides, compounds with the formula R₃PO cannot tautomerize. The situation is different for the secondary and primary phosphine oxides, with the respective formulas R₂(H)PO and R(H)₂PO.{{cite journal, doi=10.1016/S0040-4039(00)88307-0, title=Preparation and characterization of sterically protected primary phosphine sulfide and oxide, journal=Tetrahedron Letters, volume=24, issue=39, pages=4227–4228, year=1983, last1=Yoshifuji, first1=Masaaki, last2=Shibayama, first2=Katsuhiro, last3=Toyota, first3=Kozo, last4=Inamoto, first4=Naoki File:(EtO)2POH.png, diethylphosphite File:Phosphonic-acid-2D-dimensions-vector.svg,

phosphorous acid Phosphorous acid (or phosphonic acid) is the Compound (chemistry), compound described by the chemical formula, formula . It is diprotic (readily ionizes two protons), not triprotic as might be suggested by its formula. Phosphorous acid is an in ...

File:Diphenylphosphine oxide.png, Diphenylphosphine oxide File:Hypophosphorous-acid-2D.png,

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 ...

References

Functional groups Organophosphorus compounds