Magnetic resonance studies of aniline oligomers formed in the reaction of aniline with 1,1-diphenyl-2-picrylhydrazyl

Abstract

Aniline oligomers, which are formed in the reaction of aniline with 1,1-diphenyl-2-picrylhydrazyl (DPPH) in methanol and chloroform as solvents, are investigated by means of magnetic resonance techniques. The electron paramagnetic resonance (EPR) spectrum of the products of the reaction of aniline with DPPH (mole ratio, 2∶1) in chloroform solution, and of aniline with DPPH (mole ratio, 1∶2) in methanol solution, were recorded as the reaction progressed, and after the reaction was finished. The spectra of the products after reaction were resolved into the spectra of two species. For the acidified methanol solution the spectrum of one of the species shows hyperfine coupling to two nitrogen atoms with a coupling constanta(2·14N)=5.8 G, in good agreement with previously reported observations for the radical cation of model aniline trimers. A species is observed in the chloroform solution witha(1·14N)=11.4 G, which suggests the presence of aniline dimers. Both solutions also show a second signal which is attributed to higher oligomer radical cations with unresolved14N hyperfine structure.1H nuclear magnetic resonance (NMR) spectra of aniline and aniline-DPPH solutions in CDCl3 with the peaks due to DPPHH, the product of reduction of DPPH, were observed. The1H NMR experiments show that only 15% of the available aniline was consumed, in agreement with the theoretical calculations for the formation of polyaniline-emeraldine base salt under these conditions rather than the sole formation of dimers, which would be expected to consume 33% of the available aniline. This is probably due to formation of partially oxidized long-chain aniline oligomers as the main reaction product.