By means of phosphorous esters

Oxidation of the hydrolysed Grignard mixture with hydrogen peroxide or bromine provides phosphinic acids 383,398,423 however, the methyl and ethyl derivatives are difficult to isolate because of their great solubility in water, and these are better obtained by way of the diphosphane disulfides.409 Thio-phosphinic acids are obtained analogously in good yield by addition of sulfur 424 

A simple method of preparing tertiary phosphine oxides is to alkylate, by alkyl halides, the metalated secondary phosphine oxides which are intermediates 425,426 

Dialkyl thiophosphites are converted into dithiophosphinic acids by Grignard reactions followed by addition of sulfur,427 and into diphenylphosphine sulfides after reaction with phenyllithium.325 

Kabachnik and co-workers, Dokl. Akad. Nauk SSSR, 135, 603 (1960) Chem. Abstr., 55, 12272 (1961). 

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