Catalyzed oxidation of anthracene with oxygen and tert-butylhydroperoxide

Oxidation of anthracene to anthraquinone by oxygen/RhCl(PPh₃)₃ proceeds via solvent-derived hydroperoxides. tert-Butylhydroperoxide/RhCl(PPh₃)₃ effects the same transformation in up to 96% yield. Possible mechanisms for the TBHP-catalyzed reaction are discussed.     

Rh-Catalyzed Oxidation of Anthracenes with tert-Butyl Hydroperoxide. Kinetic Aspects

The polar effects of substituents on reactivity in oxidation of 2-substituted anthracenes with tert-butyl hydroperoxide (TBHP)/Rh(PPh₃)₃Cl have been investigated and compared with those obtained with TBHP/VO(acac)₂ and chromic acid. The anthracene reactivities obtained from competition experiments are correlated with Hammett's σ_p-constants. The P-values are -2.60 for chromic acid and 0.72 for TBHP/VO(acac)₂. A poor correlation with p = ?0.17 (r = 0.756) was obtained for TBHP/Rh (PPh₃)₃Cl. It is concluded that the Rh-catalyzed reaction does not consist in electrophilic oxygen transfer to the anthracene.