Comparative investigations of the electrochemical and radiation-chemical oxidation of organic sulphides

The aim of this dissertation is to study some aspects of the electrochemical and radiation-chemical oxidation of sulphur compounds. Mechanistic investigations above all were carried out with regard to the sulphoxide formation. The electrochemical oxidation of the R-S- (CH2)n-S-R which occurs through an irreversible two-electron transfer in each case, supplied the lowest oxidation potentials for n=3. This is explained by a strong auxiliary group effect between the two sulphur atom as well as through the formation of a ring in the (S.S)-3e--bonded radical cation, which results from the oxidation. This result agrees well with radiation-chemical findings where the corresponding radical cation with n=3 shows the highest stability and yield. The dependence of the oxidation potential on the inductive effect through the substitutents R showed a linear relationship with negative increase, that is, the t-butyl-substituted compound is more difficult to oxidize than the methyl-substituted. Another factor favouring the oxidationof the methyl-substituted compound energetically, is the fact that an antibonding electron is removed in the case of the further oxidation of the radical cation to the dication. This electron in the case of the methyl-substituted radical cation is on a higher energy level and is easier to extract. The same behavior is observed in the oxidation of the compounds of the type X- (CH2)n-S-R (X=halogen). Here, too, with n(CH2)=3, the lowest potentials were found, that on account of the electronegativity of the halogen decline in the following sequence: Cl > Br > I. The dependence of the potential on the inductive effect of R corresponded to that of R-S- (CH2)3-S-R and was explained correspondingly. Sulphoxide was the main product of such irreversible oxidations, which was separated and identified by HPLC. (orig./BBR)