Effects of Phenyl- and Methyl-Substituents on p-Phenylenediamine, an Electrochemical and Spectral Study

Two series of substituted p-phenylenediamines have been studied for their electronic effects on redox potential and spectral properties, p-Phenylenediamines and N,N,N',N'-tetramethyl-p-phenylenediamine substituted with different numbers of phenyl groups have been synthesized and their cyclic voltammograms have been obtained. The correlation between the substituent number and the redox potential appears linear. The slope reflects the additive effect of electron-donating methyl and electron-withdrawing phenyl groups. The absorption spectra of the cation radicals indicate that phenyl-substituted ones have broad intervalence-charge transfer bands. The p-phenylenediamines exhibit different properties from triphenylamines in that the oxidized forms are more stable in CH3CN then those in CH2Cl2. Some of the cation radicals or dications could undergo follow-up chemical reactions and form products that are more easily oxidized.