L.G. Chatten

Substituted oxindoles. Part VI. Polarographic reduction of substituted trans-3-benzylideneindol-2(3H)-ones

The polarographic reduction of a number of substituted 3-benzylideneindol-2(3H)-ones in ethanol–water (3:2 v/v) has been studied. These exhibit one or two reduction waves depending on the supporting electrolyte and the pH of the solution. Changes in E½ are discussed in terms of the Hammett σ values.

A study of the polarographic reduction of methaqualone

Abstract Methaqualone [2-methyl-3-o-tolyl-4(3H)-quinazolinone] is reduced at pH 1.5–5 in a single two-electron step. At pH 1.5–3, wave i1 appears and is gradually replaced by wave i2 which predomiantes in the solution between pH 4.5 and 6.5. At pH > 5, the height of wave i2 decreases in the shape of a dissociaton curve with increasing pH. For both waves, the diprotonated form of methaqualone (Ia) is reduced to 1,2,-dihydromethaqualone as the final product. In wave i1, the monoprotonated form Ib is further protonated at the electrode surface before it accepts the first electron; in wave i2, the free base form I accepts two protons at the electrode surface before the first electron uptake. Polarographic curves are complicated by the presence of three waves of catalytic hydrogen evolution. Wave i1, cata appears at pH 5. Citrate buffers pH 1.5–3 or Britton-Robinson buffers at pH 2.6–3.6 are most suitable for quantitative work with eitehr d.c. polarography or differential pulse polarography.