MECHANISTIC STUDIES OF ARENE OXIDE AND DIOL EPOXIDE REARRANGEMENT AND HYDROLYSIS REACTIONS

Using the semiempirical all valence electron MINDO/3 method, the mechanisms of acid-catalyzed rearrangement and hydrolysis of benzene oxide and benzene diol epoxide were studied. Both product stabilities and reaction pathways were calculated. The results show that benzene oxide prefers phenol formation to hydrolysis, and suggest that the mechanismfor this reaction involves rate-determining SN1-type formation of a carbocation quickly followed by the NIH shift, inagreement with experiment. Formation of a carbocation in benzene diol epoxide is less favorable, and should also be followed by the NIH shift leading to a ketone. Since this sort of ketone is only a minor product of the diol epoxides studied to date, it is inferred that the hydrolysis of benzene diol epoxide does not proceed by carbocation trapping, but instead by an SN2 mechanism. These results are used to rationalize why polycyclic diol epoxides are highly mutagenic and good candidates as ultimate carcinogens, whereas polycyclic arene oxides are not. © 1979, American Chemical Society. All rights reserved.