title: Kinetics of bromine-magnesium exchange reactions in substituted bromobenzenes.
abstract: Competition experiments have been performed to determine the relative reactivities of substituted bromobenzenes, bromonaphthalenes, and 9-bromoanthracene toward i-PrMgCl x LiCl in THF at 0 degrees C. The rates of the bromine-magnesium exchange reactions are accelerated by electron-acceptor substituents, the activating efficiency of which increases in the order para < meta << ortho. The activation free enthalpies of the bromine-magnesium exchange reactions correlate fairly (r(2) = 0.83) with the proton affinities of analogously substituted aryllithiums (slope 0.8). The kinetics of two representative bromoarenes with i-PrMgCl x LiCl were found to be first-order in both bromoarene and i-PrMgCl x LiCl. Combination of the resulting second-order rate constants with the k(rel) values from competition experiments allowed us to calculate reaction times for the bromine-magnesium exchange reactions of a large variety of bromoarenes.
authors.affiliation: Department Chemie und Biochemie der Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13 (Haus F), 81377 München, Germany.
authors.forename: Lei
authors.initials: L
authors.lastname: Shi
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Chu
authors.forename: Paul
authors.initials: P
authors.lastname: Knochel
authors.forename: Herbert
authors.initials: H
authors.lastname: Mayr