Anodic Oxidation of 2-Aminofluorene at a Platinum Electrode in Acetonitrile Solutions

Abstract

Abstract Anodic oxidation of 2-aminofluorene in acetonitrile solutions at a Pt electrode was investigated by using electrochemical techniques and by preparative-scale electrolyses. The cyclic voltammogram of 2-aminofluorene exhibited two anodic waves, which had peak potentials at 0.45 V (Ia) and 1.15 V (IIa) vs. Ag/0.01 M AgClO4. Wave IIa was due to oxidation of protonated 2-aminofluorene. In the voltammogram of repetitive sweeps, another redox couple (IIIa/IIIc) was observed at 0.13 V for IIIa and 0.06 V for IIIc, respectively. This indicates that at wave Ia, a species which is more easily oxidized than 2-aminofluorene was produced by follow-up chemical steps. By controlled-potential electrolysis at 0.5 V of a 2-aminofluorene solution containing pyridine as a prpton acceptor, a dark green product, 3-(2-fluorenylimino)-2,3-dihydro-2-fluorenimine (5) (or 1-(2-fluorenylimino)-1,2-dihydro-1-fluorenimine (5′)), precipitated as the main product in more than 70% yield. The oxidation pathway of 2-aminofluorene (Eqs. 1—4) has been proposed on the bases of the following results: (i) The apparent n-value was 1.95, (ii) two protons/molecule of 2-aminofluorene were released in the follow-up chemical steps, and (iii) the peak potential for oxidation of 2′-amino-2,3′-difluorenylamine (3) (or 2-amino-1,2′-difluorenylamine (3′)) was in good agreement with that of wave IIIa, and the anodic oxidation of 3 (or 3′) gave the same product as that obtained by oxidation of 2-aminofluorene.