On the electrochemistry of 2,4,6-triphenylnitrobenzene and related compounds

Cyclic voltammetry at a glassy carbon electrode of 2,4,6-triphenylnitrobenzene (1) in DMF shows two reversible one-electron reductions. Preparative reduction of 1 yields 2,4,6-triphenylaniline under both acidic and alkaline conditions and in DMF in the presence of acetic anhydride. On reduction in dry DMF is formed a stable, violet radical anion with a broad maximum at 682 nm; in acetonitrile 1 is reported to yield an unstable bluish radical which is transformed to a yellow-purple radical with a maximum at 520 nm. Solid-state 13C NMR confirmed the existence of two stereoisomers in the crystals found by X-ray structure determination, whereas 13C NMR in chloroform at ambient temperature indicated one isomer in solution. 2,4,6-Triphenylaniline shows in CV in acetonitrile a reversible oxidation; in acetonitrile containing pyridine it is oxidized to azo(2,4,6-triphenylbenzene). This compound is in acidic aqueous DMF reduced to 2,4,6-triphenylaniline. The three phenyl groups act as electron donating groups during reductions akin to p-hydroxy or p-amino groups.