Regio- and Chemoselectivity of Oxidative Conversion of Diarylamines to N,N'-Diaryldihydrophenazines and N,N'-Diarylbenzidines: DFT and Experimental Study

摘要

Detailed quantum-chemical investigation of competing routes of substituted diphenylamines oxidation was performed. Chemoselectivity as well regioselectivity of the phenazine and benzidine skeletons formation were elucidated and confirmed by experimental testing on the model diphenylamines containing CF3, Bu-t, alpha-methylcyclopropyl substituents. It was shown that the oxidation of 4,4'-disubstituted donor-acceptor amines leads to dihydrophenazines chemo- and regioselectively. For 2,4'-disubstituted donor-acceptor diphenylamines, the reaction rates for the competing reactions differ ca. 25 times in favor of the benzidine formation. Oxidation of 2,4'-disubstituted diphenylamines with electron-rich phenyl rings is much less selective; both benzidines and dihydrophenazines are formed. It was shown that the activation energy for the benzidines formation is strongly dependent on the electronic properties of the substituents in the starting amine, in contrast to the competing formation of the phenazines, which is more sensitive to sterical bulkiness of substituents.