Diethylphosphite


Diethylphosphite is the organophosphorus compound with the formula 2PH. It is a popular reagent for generating other organophosphorus compounds, exploiting the high reactivity of the P-H bond. Diethylphosphite is a colorless liquid. The molecule is tetrahedral.

Synthesis and properties

The compound was probably prepared in the 1850s by combining phosphorus trichloride and ethanol, but intentional preparations came later. It arises as follows:
Many derivatives can be prepared similarly. Despite being named as a phosphite it exists overwhelmingly in its phosphonate form,, a property it shares with its parent acid phosphorous acid; despite this many of its reactions are difficult to rationalise without assuming the existence of the following tautomerism equilibrium between phosphorus and phosphorus forms:

Reactions

Alkoxide exchange

Diethylphosphite 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:

P-alkylation

Diethylphosphite undergoes deprotonation with potassium tert-butoxide. This reactivity allows alkylation at phosphorus:
For converting aryl halides, palladium-catalysis can be employed. The C-P coupling process is reminiscent of the Buchwald-Hartwig amination.
Reaction of diethylphosphite with Grignard reagents results in initial deprotonation followed by displacement of the ethoxy groups. This reactivity provides a route to secondary phosphine oxides, such as dimethylphosphine oxide as shown in the following pair of idealized equations:

Hydrophosphonylation

Diethylphosphite can add across unsaturated groups via a hydrophosphonylation reaction. For example, it adds to aldehydes in a manner similar to the Abramov reaction:
It can also add to imines in the Pudovik reaction and Kabachnik–Fields reaction, in both cases forming aminophosphonates