Aryl Proton Transfer Reactions of 9-Arylanthracene and 9-Substituted Anthracene Radical Cations with 2,6-Di-tert-butylpyridine

Article abstract of DOI:10.1021/jo00101a015

Radical cations of anthracenes with substituents at the 9-position (Br, CN, or NO2) or those of 9-arylanthracenes were observed to undergo proton transfer reactions with 2,6-di-tert-butylpyridine (TBP) to generate the corresponding anthracenyl radical.Under the same conditions 2,6-dimethylpyridine (LUT) undergoes combination reactions with the radical cations, and the proton transfer reactions could not be detected.The characteristic features of the reactions producing the anthracenyl radicals are as follows: (a) primary deuterium kinetic isotope effects are observed on substitution of the 10-H with 10-D, (b) the apparent Arrhenius activation energies vary from -2 to -11 kcal/mol, and (c) 10-Br-substituted anthracenes are formed during bromine atom abstraction from bromoform by the free radicals.The intermediate bromo derivatives are further oxidized under the reaction conditions.A two-step mechanism involving a reversible ?-complex formation followed by rate-determining proton transfer is proposed.The results of the reactions with TBP are compared to those obtained from the corresponding reactions of the radical cations with LUT.