Alkoxyphosphonium Salts. 3. Kinetics and Thermodynamics in Alkylation by Alkoxyphosphonium Salts

Article abstract of DOI:10.1021/jo00335a009

Several methoxyphosphonium trifluoromethanesulfonates (triflates) are characterized by the rates of methyl transfer to the 2,4-dinitrophenoxide ion.In acetone at 25 deg C, the measured second-order rate constants range from about 0.2 to about 40 M^-1s^-1, putting substances of this class among the most powerful methylating agents.The methylating power is confirmed by the measurement of the equilibrium extent of methylation of the counterion, the triflate ion.The Arbuzov rearrangement of trimethyl phosphite is slow with the catalyst methyl iodide but is fast enough with the cata lyst methyltrimethoxyphosphonium triflate to allow calorimetric measurement for the conversion of trimethyl phosphite to dimethyl methylphosphonate; ΔH = -24 +/- 2 kcal/mol.An earlier error in the measurement of the rate of this reaction is corrected, so that the mechanism of the methyl iodide catalyzed Arbuzov reaction of trimethyl phosphite is no longer in question; the first step is rate-determining.