By means of phosphoryl halides

Partial reaction of phosphoryl chloride with amines can be used for synthesis of phosphonic acids 392,393 if applied to phosphonic dichlorides it affords unsymmetrical phosphinic acids.396 

Tertiary phosphine oxides are obtained from phosphinic chlorides and Grignard reagents,397 and ditertiary phosphine oxides similarly from di-Grignard reagents.398 

Ethyldiphenylphosphine oxide 397 Diphenylphosphinic acid (0.22 g) is converted into the acid chloride by 1-2 hours boiling under reflux with thionyl chloride (0.5 ml) in toluene. About half the solvent is then distilled off and the residual solution is diluted with benzene and dropped at room temperature into a Grignard solution prepared from magnesium (0.25 g) and ethyl bromide (2.5 ml). The reaction is complete after half an hour s boiling under reflux. The product is hydrolysed by ice and hydrochloric acid, the aqueous layer is washed with ether, and ether phases are united, dried, and evaporated. The residue is subjected to steam-distillation and then extracted several times with ether. The residue left on evaporation of these extracts crystallizes at once or on short storage and is decolorized in acetone by charcoal. Recrystallization from ether-light petroleum or aqueous acetone affords the oxide, m.p. 123-124° (67%). 

Unlike the phosphorus chlorides mentioned above, thiophosphoryl chloride reacts with alkylmagnesium halides to form tetraalkyldiphosphane disulfides which contain a P-P bond 402-411 

particularly for the lower homologs, yields are good and the P-P bond can be cleaved readily, this reaction provides a preparatively important route to the phosphinic acid series. 

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