Dehalogenation reactions of vicinal dihalides. Part III. Dehalogenations of 1-chloro-2-iodo-1,2-diphenylethane induced by a variety of nucleophiles. The nucleophilic reactivity towards iodine

Abstract

Dehalogenations of erythro-1-chloro-2-iodo-1,2-diphenylethane promoted by a variety of nucleophiles have been studied in methanol and, in the case of halide ions, also in NN-dimethylformamide. The susceptibility of iodine in this compound to undergo nucleophilic attack is extremely high and surpasses that of bromine by a factor larger than 10⁶. An order of nucleophilic reactivity towards iodine bonded to a saturated carbon has been established. Dehalogenation rates follow approximately the Edwards equation with α and β values (2·13 and –0·12, respectively) indicating that polarizability and desolvation factors play a larger role than basicity in determining nucleophilic reactivity. The importance of the polarizability is also shown by the reactivity order of the halide ions in dimethylformamide which is I^– > Br^– > Cl^–. As an electrophilic centre, iodine appears to have a susceptibility to be attacked by polarizable nucleophilies which is larger than that of the saturated carbon atom.