Diethylphosphite

Diethyl phosphite is the organophosphorus compound with the formula (C₂H₅O)₂P(O)H. It is a popular reagent for generating other organophosphorus compounds, exploiting the high reactivity of the P-H bond. Diethyl phosphite is a colorless liquid. The molecule is tetrahedral.

The compound was probably prepared in the 1850s by combining phosphorus trichloride and ethanol, but intentional preparations came later. It arises as follows:

Under similar conditions but in the presence of base, triethyl phosphite results:

Many analogues of diethyl phosphite can be prepared. Despite being named as a phosphite the compound exists overwhelmingly in its phosphonate form, (C₂H₅O)₂P(O)H, a property it shares with its parent acid phosphorous acid. Nonetheless many of its reactions appear to proceed via the minor phosphorus(III) tautomer.

Diethyl phosphite hydrolyzes to give phosphorous acid. Hydrogen chloride accelerates this conversion.:

Diethyl phosphite undergoes transesterification upon treating with an alcohol. For alcohols of high boiling points, the conversion can be driven by removal of ethanol:

Similarly amines can displace ethoxide:

Diethyl phosphite undergoes deprotonation with potassium tert-butoxide. This reactivity allows alkylation at phosphorus (Michaelis–Becker reaction):