Kinetic studies of the reactions of 2-alkylsulphonyl-, 2-alkylsulphinyl-, and 2-alkylthio-quinoxalines with sodium methoxide showed that for the methyl, ethyl, isopropyl, and t-butyl compounds a decreased reactivity was observed with increasing size of the group. This effect was least for the sulphides (1·8 fold difference) and greatest (140 fold) for sulphoxides. U.v. and ¹H n.m.r. spectra are recorded and discussed.