Phosphinous acids

Phosphinous acids are usually organophosphorus compounds with the formula R2POH.

[1] It is prepared in several steps from phosphorus trichloride (Et = ethyl):[2] With the lone exception of the bis(trifluoromethyl) derivative, the dominant reaction of phosphinous acids is tautomerization: Even the pentafluorophenyl compound P(C6F5)2OH is unstable with respect to the phosphine oxide.

[2] Although phosphinous acids are rare, their P-bonded coordination complexes are well established, e.g.

[3] 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.