Polar Radicals. 16. Comments on a Recently Published Mechanistic Study of Photobromination Using Bromotrichloromethane

Article abstract of DOI:10.1021/jo01313a032

The mechanism of the photobromination reactions of a series of 10-substituted 9-methylanthracenes with bromotrichloromethane was reexamined.It was shown, contrary to the previous report, that the reaction proceeded by a mixed chain involving abstraction by both the bromine atom and the trichloromethyl radical.The kinetic results obtained from these reactions were shown to be dominated by reversible hydrogen transfer of the radicals formed in the reaction with the small amounts of hydrogen bromide produced from bromine atom abstraction.When the reactions were carried out in the presence of a hydrogen bromide scavenger, either ethylene oxide or powdered potassium carbonate, the kinetc results of photobromination were found to be almost insensitive to the effects of the changes in substituents.The reactivities of fluorene relative to the 10-substituted 9-methylanthracenes were found to be anomalously high, as was previously reported; however, when the reactions were carried out in the presence of ethylene oxide, the relative reactivities were shown to be predictably almost the same as those obtained when tert-butoxy radicals were the abstracting species.