Phosphinous acids are usually organophosphorus compounds 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 are tetrahedral and are 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 toxi ...

(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 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 relocation of a hyd ...

: :PR₂OH → OPR₂H Even the pentafluorophenyl compound P(C₆F₅)₂OH is unstable with respect to the phosphine oxide. Although phosphinous acids are rare, their P-bonded

coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as '' ligands'' or complexing agents. ...

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 (singular)) is the compound described by the formula H3PO3. This acid is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in th ...

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 this ...

References

Functional groups Organophosphorus compounds