Kinetics of bromine-magnesium exchange reactions in substituted bromobenzenes.

Lei Shi, Yuanyuan Chu, Paul Knochel, Herbert Mayr

文献索引：J. Org. Chem. 74(7) , 2760-4, (2009)

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摘要

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.