Dimethylphosphine oxide
# Dimethylphosphine oxide

Dimethylphosphine oxide is an organophosphorus compound with the formula $(CH_3)_2P(O)H.$ 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.

## Preparation

The compound arises by the hydrolysis of chlorodimethylphosphine:

    $Me_2PCl$ + $H_2O$ → $Me_2P(O)H$ + 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:

    $(C_2H_5O)_2P(O)H$ + 3 $CH_3MgBr$ → $(CH_3)_2P(O)MgBr$ + 2 $MgBr(OC_2H_5)$ + $CH_4$
    $(CH_3)_2P(O)MgBr$ + $H_2O$ → $(CH_3)_2P(O)H$ + 2 MgBr(OH)

## Reactions

Chlorination gives dimethylphosphoryl chloride. It undergoes hydroxymethylation with formaldehyde.

    $Me_2P(O)H$ + $CH_2O$ → $Me_2P(O)CH_2OH$

Many aldehydes effect a similar reaction.

