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Rates and Equilibria of the Reactions of Tertiary Phosphanes and Phosphites with Benzhydrylium Ions

โœ Scribed by Bernhard Kempf; Herbert Mayr

Publisher
John Wiley and Sons
Year
2005
Tongue
English
Weight
202 KB
Volume
11
Category
Article
ISSN
0947-6539

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โœฆ Synopsis

Abstract

The kinetics of the reactions of benzhydrylium ions and quinone methides with eight tertiary phosphanes and two phosphites were investigated photometrically. The nucleophilicity parameters N and slope parameters s of these nucleophiles were derived according to the equation logโ€‰k~20โ€‰ยฐC~ = s(N + E). Correlations of the nucleophilicity parameters N with p__K__~Ha~ and ฯƒ~p~ values as well as with the rate constants of reactions with other electrophiles are discussed. In some cases, equilibrium constants for the formation of phosphonium ions were measured, which allow one to determine the Marcus intrinsic barriers of ฮ”__G__~0~^โ‰ ^ = 58 kJโ€‰mol^โˆ’1^ for the reactions of triarylphosphanes with benzhydrylium ions. The N parameters [5.51 for P(OPh)~3~, 10.36 for P(OBu)~3~, 14.33 for PPh~3~, 15.49 for PBu~3~, 18.39 for P(4โ€Me~2~NC~6~H~4~)~3~] are compared with the reactivities of other classes of nucleophiles (see, www.cup. uniโ€muenchen.de/oc/mayr).

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