Nonetheless many of its reactions appear to proceed via the minor phosphorus(III) tautomer.

For alcohols of high boiling points, the conversion can be driven by removal of ethanol:[8] Similarly amines can displace ethoxide:[9] Diethyl phosphite undergoes deprotonation with potassium tert-butoxide.

This reactivity allows alkylation at phosphorus (Michaelis–Becker reaction):[10] For converting aryl halides, palladium-catalysis can be employed.

Reaction of diethyl phosphite with Grignard reagents results in initial deprotonation followed by displacement of the ethoxy groups.

[11][12] This reactivity provides a route to secondary phosphine oxides, such as dimethylphosphine oxide as shown in the following pair of idealized equations: Diethyl phosphite can add across unsaturated groups via a hydrophosphonylation reaction.