The intermediates in the replacement of hydrogen in 2-quinoxalone by arylamines were recorded by PMR spectroscopy. The synthesized model compounds - 3,4-dihydro-3-R-quinoxal-2-ones - are spectrally identical to the observed intermediates. Under the reaction conditions they undergo reversible decomposition to the starting compounds and are oxidized to give the reaction products. 6-Nitro-2-quinoxalone forms stable addition products in the reaction with arylamines. The polarographic oxidation of 3,4-dihydro-3-R-quinoxal-2-ones and the model compounds shows that primarily the dihydro fragment of the molecule is oxidized.