By the Oxidation of Phosphorus III Compounds

In principle, any phosphorus(III) compound possessing one (phosphonous acid derivative) or two (phosphinous acid derivative) P—C bonds may be oxidized to the corresponding derivative of the quinquevalent phosphonic or phosphinic acid. In practice, this might be difficult to achieve because of the extremely high reactivity of the phosphorus(III) compound in oxidation under both anhydrous or aqueous conditions, and it might also prove inconvenient because of difficulties in the synthesis of the phosphorus(III) compound. Alternative synthetic routes are always available. A phosphonous dichloride (dichlorophosphine) (317) may be converted into the phosphonic diester 319 by way of the phosphonous diester 318 alternatively, the original dichloride 317 may be first oxidized to the phosphonic dichloride 320 before esterification to 319 a similar sequence exists for the phosphinous-phosphinic series. 

In a novel procedure, trichloroacetic acid acts on phosphorus(III) chlorides with the formation of the corresponding phosphorus(V) chloride together with dichloroacetyl chloride  

The conversion of an aryldichlorophosphine into the phosphonic dichloride, directly or indirectly, has been widely described. Aryltetrafluorophosphoranes are converted into the corresponding phosphonic difluorides with hexamethyldisiloxane or other similar silicon compounds A constant-boiling mixture of PhP(0)F2 and PhP(S)F2 is obtained from KSO2F and PhPCl2 Trichlorodiphenylphosphorane and MeOPCl2 give diphenylphosphinic acid in 92% yield.  

Reactions between alkyl iodides and red phosphorus with iodine or P2I4 afford the phosphoranes R2PI3, which on hydrolysis yield the dialkyIphosphinic acids  

At this juncture, it may be noted that aryltetrachlorophosphoranes have been used to provide a wide range of derivatives of arylphosphonic and diarylphosphinic acids, as 

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