Abstract: Kinetic studies on the nucleophilic substitution reaction of Y-substituted phenylmethanesulfonyl halides with X-substituted anilines in methanol-acetonitrile have been carried out in order to elucidate the reaction mechanism. The phenylmethanesulfonyl fluorides (PSF) had markedly lower rates and smaller magnitudes of px and py values compared with those for the chlorides (PSC). On the contrary, however, the magnitude of ...