Phosphinous acids


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 is tetrahedral and is assigned oxidation state V.

Synthesis

Only one example is known, bisphosphinous acid, 2POH. It is prepared in several steps from phosphorus trichloride :

Reactions

With the lone exception of the bis derivative, the dominant reaction of phosphinous acids is tautomerization:
Even the pentafluorophenyl compound P2OH is unstable with respect to the phosphine oxide.
Although phosphinous acids are rare, their P-bonded coordination complexes are well established, e.g. Mo5P3.

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 R2PO and R2PO.