Polarography of nitro and carbonyl derivatives of arylfurans in anhydrous dimethylformamide

Abstract

It is shown that the first reversible one-electron wave in the reduction of 5-arylfurans in anhydrous dimethylformamide (DMF) corresponds to the formation of an anion radical and that the subsequent waves are associated with cleavage of the C-Hal bond in the case of halo derivatives and with reduction of the anion radical and the arylfuran fragment. The character of the reduction of 5-(p-nitrophenyl)furan derivatives is determined by the ability of the substituent in the 2 position to delocalize the negative charge. In conformity with this, the first two reversible waves of carbonyl-substituted derivatives are one-electron waves and correspond to the formation of a stable dianion, the greatest contribution to the resonance hybrid of which is made by a p-quinoid structure. The second wave of 5-(p-nitrophenyl)furan and its 2-CH2OH derivative is irreversible and corresponds to the transfer of three electrons. Lithium ions have a substantial effect on the height and E1/2 value of the second reduction wave, and this effect is manifested more markedly, the less the substituent in the 2 position is capable of delocalizing the negative charge. The transmission factor of the furan ring is 0.48.