The effect of α-cyclodextrin upon the kinetics of aqueous bromination of anisole

Abstract

α-Cyclodextrin (cyclohexaamylose) (CD) reduces the rate of bromination of anisole and p-methylanisole in aqueous KBr solutions (0.05–0.1 M). This retardation is largely due to the formation of a CD – tribromide ion complex and, to a lesser extent, to the encapsulation of bromine and of the anisole substrate. For p-methylanisole no other effects seem to be important. However, for anisole a pathway involving free (or complexed) anisole and complexed (or free) bromine seems to be operative. The intermediacy of a ternary complex (CD–anisole–Br2) cannot be ruled out. Both equilibrium and kinetic measurements indicate that the dissociation constant of the CD–Br3− complex is ~2 × 10−4 M.