Physico-chemical studies on areno-tropilidenes and tropones. I. The polarographic behaviour and electron affinities of thiophenotropone derivatives in buffer solutions of varying pH values and in DMF

Abstract

The polarographic behaviour of some thiophenotropone derivatives were studied in DMF and in Thiel buffer solutions of varying pH values and μ of 0.1 at 25 ± 0.1 °C. It was found that the carbonyl group is the active centre towards reduction. In strong acid media, the reduction proceeds via one reversible electron forming a free radical which dimerises to produce pinacol. In solutions of pH values from 4 to 9, the polarograms consist of two reduction waves of equal heights each corresponding to 1 F. In strong alkaline media, one wave is observed; in most cases, depending on the molecular structure, the wave corresponds to the uptake of two electrons. The first step involves the direct reduction of the basic form to the anion radical which undergoes a further reduction forming the corresponding thiophenotropolone. At pH values > 13, the height of the limiting current decreases until it attains the height corresponding to 1 F indicating that the anion radical is stable in such media. Also, the electron affinities of these compounds were calculated.