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
CAS Number	7211-39-4
3D model (JSmol)	Interactive image
ChemSpider	10415346
EC Number	230-591-2
PubChem CID	81631
InChI InChI=1S/C2H7OP/c1-4(2)3/h4H,1-2H3 Key: HGDIHUZVQPKSMO-UHFFFAOYSA-N
SMILES CP(=O)C
Properties
Chemical formula	C2H7OP
Molar mass	78.051 g·mol−1
Appearance	colorless liquid
Boiling point	65–67 °C
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H315, H319, H335
Precautionary statements	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.