Reactivity studies of S‐methylthiophenium tetrafluoroborates

Abstract

AbstractThe polarographic behavior of four S‐methylthiophenium tetrafluoroborates, I‐IV, has been investigated in Britton‐Robinson aqueous buffers. The compounds under study were the S‐methylbenzo[b]thiophenium (I), S‐methylnaphtho[2,3‐b]thiophenium (II), S‐methyldibenzothiophenium (III), and S‐methylnaphtho[2,1‐b]thiophenium (IV) tetrafluoroborates which were obtained from the parent sulfur heterocycles by their reaction with methyl iodide and silver tetrafluoroborate in 1,2‐dichloroethane, II and IV being new compounds. Compounds I‐IV give two one‐electron reduction waves and the more positive wave appears to be associated with an electron transfer from the electrode to the LUMO of the substrate as indicated by the experimental E1/2 vs calculated LUMO values plot (Figure 2). The rates of demethylation of the ions I‐IV with the iodide ion acting as the nucleophile have been determined in the Britton‐Robinson buffer (pH 6)‐acetonitrile solution at 24°. The results of the polarographic study and of the kinetic studies with the iodide ion confirm the high reactivity of S‐methylthiophenium ions which originates in the antiaromatic destabilization of these structures.