Diethylphosphite
| Names | |
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| Preferred IUPAC name
Diethyl phosphonate | |
| Other names
diethyl phosphonite; DEP; Phosphonic acid, diethyl ester
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3D model (JSmol)
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| 4-01-00-01329 | |
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PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| C4H11O3P | |
| Molar mass | 138.103 g·mol−1 |
| Appearance | colorless liquid |
| Density | 1.072 g/cm3 |
| Boiling point | 50-51 °C at 2 mm Hg |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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.[1] The molecule is tetrahedral.
Synthesis and properties
[edit | edit source]The compound was probably prepared in the 1850s by combining phosphorus trichloride and ethanol, but intentional preparations came later. It arises as follows:[2]
- PCl3 + 3 C2H5OH → (C2H5O)2P(O)H + 2 HCl + C2H5Cl
Under similar conditions but in the presence of base, triethyl phosphite results:[3]
- PCl3 + 3 EtOH + 3 R3N → P(OEt)3 + 3 R3NH + 3 Cl−
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 acid phosphorous 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]
Reactions
[edit | edit source]Hydrolysis and alcoholysis
[edit | edit source]Diethyl phosphite hydrolyzes to give phosphorous acid. Hydrogen chloride accelerates this conversion.:[2]
Diethyl phosphite undergoes transesterification upon treating with an alcohol. For alcohols of high boiling points, the conversion can be driven by removal of ethanol:[8]
- (C2H5O)2P(O)H + 2 ROH → (RO)2P(O)H + 2 C2H5OH
Similarly amines can displace ethoxide:[9]
- (C2H5O)2P(O)H + RNH2 → (C2H5O)(RN(H)P(O)H + C2H5OH
P-alkylation
[edit | edit source]Diethyl phosphite undergoes deprotonation with potassium tert-butoxide. This reactivity allows alkylation at phosphorus (Michaelis–Becker reaction):[10]
- (C2H5O)2P(O)H + KOtBu → (C2H5O)2P(O)K + HOtBu
- (C2H5O)2P(O)K + RBr → (C2H5O)2P(O)R + KBr
For converting aryl halides, palladium-catalysis can be employed.[1] The C-P coupling process is reminiscent of the Buchwald-Hartwig amination.
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:
- (C2H5O)2P(O)H + CH3MgBr → (C2H5O)2P(O)MgBr + CH4
- (C2H5O)2P(O)MgBr + 2 CH3MgBr → (CH3)2P(O)MgBr + 2 MgBr(OC2H5)
- (CH3)2P(O)MgBr + H2O → (CH3)2P(O)H + MgBr(OH)
Hydrophosphonylation
[edit | edit source]Diethyl phosphite can add across unsaturated groups via a hydrophosphonylation reaction. For example, it adds to aldehydes in a manner similar to the Abramov reaction:
- (C2H5O)2P(O)H + RCHO → (C2H5O)2P(O)CH(OH)R
It can also add to imines in the Pudovik reaction and Kabachnik–Fields reaction,[13] in both cases forming aminophosphonates
See also
[edit | edit source]References
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