Dimethylphosphine oxide

Dimethylphosphine oxide is an organophosphorus compound with the formula (CH3)2P(O)H. It is a colorless liquid that soluble in polar organic solvents. It exists as the phosphine oxide, not the hydroxy tautomer. A related compound is diphenylphosphine oxide. Both are sometimes called secondary phosphine oxides.

Dimethylphosphine oxide
Names
Preferred IUPAC name
Dimethyl-λ5-phosphanone
Other names
dimethylphosphinous acid tautomer
Identifiers
3D model (JSmol)
ChemSpider
EC Number
  • 230-591-2
  • InChI=1S/C2H7OP/c1-4(2)3/h4H,1-2H3
    Key: HGDIHUZVQPKSMO-UHFFFAOYSA-N
  • CP(=O)C
Properties
C2H7OP
Molar mass 78.051 g·mol−1
Appearance colorless liquid
Boiling point 65–67 °C
Hazards
GHS labelling:
GHS07: Exclamation mark
Warning
H302, H315, H319, H335
P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P340, P305+P351+P338, P312, P321, P330, P332+P313, P337+P313, P362, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Preparation

The compound arises by the hydrolysis of chlorodimethylphosphine:[1]

Me2PCl + H2O → Me2P(O)H + HCl

Methanol, but not ethanol, can also be used in place of water, the co-product being methyl chloride.

Since chlorodimethylphosphine is dangerous to handle, alternative routes to dimethylphosphine oxide have been developed. A popular method starts with diethylphosphite, according to the following idealized equations:[2]

(C2H5O)2P(O)H + 3 CH3MgBr → (CH3)2P(O)MgBr + 2 MgBr(OC2H5) + CH4
(CH3)2P(O)MgBr + H2O → (CH3)2P(O)H + 2 MgBr(OH)

Reactions

Chlorination gives dimethylphosphoryl chloride. It undergoes hydroxymethylation with formaldehyde.

Me2P(O)H + CH2O → Me2P(O)CH2OH

Many aldehydes effect a similar reaction.

References
  1. Kleiner, H. J. (1974). "Herstellung und Umsetzungen von Dimethylphosphinoxid (Preparation and Reactions of Dimethylphosphine Oxide)". Justus Liebigs Ann. Chem.: 751–764. doi:10.1002/jlac.197419740507.
  2. Hays, H. R. (1968). "Reaction of diethyl phosphonate with methyl and ethyl Grignard reagents". J. Org. Chem. 33: 3690–3694. doi:10.1021/jo01274a003.
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