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Dimethylphosphine oxide

Dimethylphosphine oxide is an organophosphorus compound with the formula (CH<sub>3</sub>)<sub>2</sub>P(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.

Preparation

The compound arises by the hydrolysis of chlorodimethylphosphine:

Me<sub>2</sub>PCl + H<sub>2</sub>O → Me<sub>2</sub>P(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:

(C<sub>2</sub>H<sub>5</sub>O)<sub>2</sub>P(O)H + 3 CH<sub>3</sub>MgBr → (CH<sub>3</sub>)<sub>2</sub>P(O)MgBr + 2 MgBr(OC<sub>2</sub>H<sub>5</sub>) + CH<sub>4</sub>
(CH<sub>3</sub>)<sub>2</sub>P(O)MgBr + H<sub>2</sub>O → (CH<sub>3</sub>)<sub>2</sub>P(O)H + 2 MgBr(OH)

Reactions

Chlorination gives dimethylphosphoryl chloride. It undergoes hydroxymethylation with formaldehyde.

Me<sub>2</sub>P(O)H + CH<sub>2</sub>O → Me<sub>2</sub>P(O)CH<sub>2</sub>OH

Many aldehydes effect a similar reaction.

References