SIDE-CHAIN BROMINATION OF ALPHA-SUBSTITUTED TOLUENES BY N-BROMOSUCCINIMIDE . A REVISION AND EXTENSION OF PREVIOUS OBSERVATIONS

Values for the relative reactivities of α-substituted toluenes with N-bromosuccinimide which have been obtained in previous investigations are not in complete agreement. The reactivities have, therefore, been redetermined through competition experiments using nmr techniques for analysis of the product mixtures. Application of the nmr method has made possible, in most instances, the cross-checking of both the quantities of reactants consumed and the quantities of α-bromotoluene derivatives produced. The logarithms of the relative reactivities of the various α-substituted toluene derivatives (C6H4CH3X) show a reasonably goodpσ correlation using the σp+ values of the substituents X; the p value is substantially more negative (-2.46) than that observed previously for the reactions of ring-substituted toluenes (XC5H4CH3) with N-bromosuccinimide under similar conditions. Thus, appreciable polarization of the benzylic carbon presumably occurs during the activation processes of these reactions. © 1969, American Chemical Society. All rights reserved.