By means of phosphorus triesters

When heated with alkyl halides at temperatures between 100° and 200°, phosphorous triesters containing at least one P-Oalkyl group afford phos-phonic diesters  

This procedure, known as the Michaelis-Arbuzov reaction,251 is one of the oldest but still one of the most important methods of forming P-C bonds. 

When R = R the reaction amounts to isomerization of the phosphite to phosphonate, and then catalytic amounts of alkyl halide suffice. 

Dimethyl methylphosphonate 352 Trimethyl phosphite (0.1 mole) is heated with methyl iodide (10 mmoles) at 100° for 30 min. After a short induction period a violent reaction sets in which is complete in a few minutes. Distillation in a vacuum gives a 93 % yield of the phosphonate, b.p. 63°/10 mm. When only 1 mmole of methyl iodide is used, the yield of phosphonate amounts to about 80%. 

The nucleophilicity of the trivalent phosphorus and thus the reactivity increases with increasing +/ effect of substituents on the phosphorus atom. The phosphonous esters and, more so, phosphinous esters undergo the Arbuzov reaction more readily than do phosphorous esters.253 Methyl diphenylphos-phinite, for instance, reacts exothermally with methyl iodide even at room temperature, giving the isomeric phosphine oxide 254 although it is usual to work without a solvent, it is advisable to moderate the often very exothermic reaction of phosphonites by dilution with the reaction product and by carefully controlled portionwise addition of phosphonite. 

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