Diethyl phosphite is theorganophosphorus 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.[1] The molecule istetrahedral.
The compound was probably prepared in the 1850s by combiningphosphorus trichloride and ethanol, but intentional preparations came later. It arises as follows:[2]
Many analogues of diethyl phosphite can be prepared.[4][5] 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 acidphosphorous acid. Nonetheless many of its reactions appear to proceed via the minor phosphorus(III)tautomer.[6]
(C2H5O)2PIII(OH) ⇌ (C2H5O)2PV(O)H, K = 15 x 106 (25°C, aqueous)[7]
Diethyl phosphite hydrolyzes to give phosphorous acid. Hydrogen chloride accelerates this conversion.:[2]
Diethyl phosphite undergoestransesterification upon treating with an alcohol. For alcohols of high boiling points, the conversion can be driven by removal of ethanol:[8]
For converting aryl halides, palladium-catalysis can be employed.[1] The C-P coupling process is reminiscent of theBuchwald-Hartwig amination.
Reaction of diethyl phosphite withGrignard reagents results in initial deprotonation followed by displacement of theethoxy groups.[11][12] This reactivity provides a route to secondary phosphine oxides, such asdimethylphosphine oxide as shown in the following pair of idealized equations:
^Fakhraian, H.; Mirzaei, A. (2004). "Reconsideration of the Base-Free Batch-Wise Esterification of Phosphorus Trichloride with Alcohols".Org. Process Res. Dev.8 (3):401–404.doi:10.1021/op049958v.
^Doak, G. O.; Freedman, Leon D. (1961). "The Structure and Properties of the Dialkyl Phosphonates".Chem. Rev.61 (1):31–44.doi:10.1021/cr60209a002.
^Hays, Hugh R. (1968). "Reaction of diethyl phosphonate with methyl and ethyl Grignard reagents".J. Org. Chem.33 (10):3690–3694.doi:10.1021/jo01274a003.
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