Alkoxyphosphonium ions. 5. Kinetics of the Michaelis–Arbuzov intermediate

Abstract

156 (1986).Rates of formation and destruction of the alkoxyphosphonium ion, the intermediate in the Michaelis-Arbuzov reactions of some methyl esters of trivalent phosphorus acids with methyl iodide, are followed by a conductivity method in the solvent propylene carbonate. Specific conductances of the unstable intermediates are well estimated through stable model salts. Rate constants for both the alkylationof the reagent and the dealkylation of the intermediate are obtained. The conductivity time curves are simulated by adjusting rate constants for two sequential second order reactions, assuming no ion pairing at the concentrations used. In these measurements of the intermediate only, there is no rate-determining step; for the overall reaction the first step is in most cases rate-determining. Optrant dans le carbonate de propylkne comme solvant et faisant appel i une mtthode de conductivitk, on a dttermint les vitesses de formation et de destruction de I'ion alkylphosphonium, I'intemtdiaire dans les rtactions de Michaelis-Arbuzov de quelques esters mtthyliques d'acides phosphoreux trivalents avec I'iodure de mtthyle. En se basant sur des sels modbles stables, on a pu bien Cvalut les conductivitts sptcifiques des intermtdiaires instables. On a pu dkterminer les constantes de vitesse tant de I'alkylation du rtactif que de la dtalkylation de I'intermtdiaire. Faisant I'hypothkse qu'il n'y a pas de couplage d'ions ux concentrations utilistes, on a simult les courbes de conductivitk vs. temps en ajustant les constantes de vitesse pour deux rtactions du deuxi&me ordre qui se suivent. Dans ces mesures qui n'impliquent que I'intermtdiaire, il n'y a pas d'ttape dtterminante; pour I'ensemble de la rkaction, la premibre ttape est gtnkralement I'ktape qui dttermine la vitesse. IntroductionUp to now, kinetic studies of the Arbuzov reaction have not provided the precision needed to uncover the possible mechanistic complexities, and to allow studies of structurereactivity relations. This interesting reaction has been neglected quantitatively, in part because many potential analyses such as absorption or titration for the reagents or products are inapplicable or undeveloped.The first reasonably successful method, by Aksnes and Aksnes (I), used an infrared analysis based upon the formation of the characteristic P=O bond in the product, leading to the still accepted conclusion that in that case the first alkylation step was rate-detemining. This analysis is cumbersome, slow, and of limited precision; we have not found it attractive for our studies. Our attempts to substitute a gas chromatographic analysis did not overcome these problems, but a nmr method showed promise as a highly compound-specific method. This was in fact successful at the level of seeing compounds at fairly high concentrations and it allowed the observation of the intermediate alkoxyphosphonium salt and rough rate studies using both proton and phosphorus nmr (2). Studies of structure reactivity relations were unconvincing. Nevertheless, the mechanisms were cle...

Novel 2‐phosphabicyclo[2.2.2]oct‐5‐ene derivatives and their use in phosphinylations

“…(9) [19] A 15 ml toluene solution containing 0.80 g (3.35 mmol) of dihydrophosphinine oxide 1 [16] consisting of 75% of the A and 25 % of the B isomer and 0.50 g (4.63 mmol) of benzoquinone was stirred at boiling point for 4 days. The solvent was evaporated, and the residual material purified by flash chromatography as above to furnish 0.42 g (36%) of product 8 consisting of four isomers (δ P 32.0 (34%), 38.1 (17%), 38.2 (15%), and 40.5 (34%)).…”