The oxidative phosphonation of alkanes

This procedure, although not widely used since it does indeed have some severe restrictions, has nevertheless proved useful in a few cases. The reaction involves bubbling oxygen or air through a mixture of the hydrocarbon and PCI3 and the results accord with equation 26. The case most widely reported and one which has always provided excellent results is that of cyclohexane % and it has been claimed that a second dichlorophosphonylation step can occur Ethyl or methyl dichlorophosphites can be used to replace the PCl3.  

Although the reaction requires no catalysis, and is not catalysed by AICI3,12, iron or BF3, the drawbacks to the procedure are (i) a large wastage of the trichloride as POCI3 (ii) a lack of regiospecificity clearly demonstrable in the reactions of linear or non-symmetrical 

To a very limited degree, the procedure has been applied to the preparation of selected phosphinic chlorides of these, reactions involving methyl- and ethylphosphonous dichlo-rides and PhPCl2, in conjunction with cyclohexane, successfully lead to the phosphinic chlorides, CyRP(0)Cl (R = Me, Et, or Ph). 

The reaction often fails if the reactants, particularly the hydrocarbon, are purified to a high degree, and it has therefore been suggested that the mechanism of the reaction is one involving free radicals, on the assumption that purification of the hydrocarbon removed peroxide impurities. The substitution occurs most readily at a teriary carbon site and least easily at a primary carbon. Radical mechanisms were proposed by Soborovskii et al and later by Flurry and Boozer .  

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