Testing the Veracity of Claims of Lewis Acid Catalysis

Abstract Are reactions employing Lewis acids really catalysed by those Lewis acids, or by “hidden Bronsted acids”, i.e. Bronsted acids generated in situ by hydrolysis? Testing of a series of reactions using Sc(III), Fe(III), In(III) and Y(III) by addition of 2,6-di- t -butyl-4-methylpyridine reveal that all are likely to follow the latter pathway. A reaction claimed to be catalysed by CBr 4 through halogen bonding is also likely to be Bronsted acid catalysed.