The specific rates of solvolysis of phenyl chlorothionoformate (PhOCSCl) are remarkably similar to those previously reported for phenyl chlorothioformate (PhSCOCl). When analyzed using the extended Grunwald-Winstein equation over the usual range of solvent types, these solvolyses show essentially identical divisions into the solvents favoring the addition-elimination channel and those favoring the ionization channel. The introduction of one sulfur caused a partial shift away from the addition-elimination pathway, which was dominant over the full range of solvents for phenyl chloroformate (PhOCOCl). Consistent with these results, introduction of the second sulfur within phenyl chlorodithioformate (PhSCSCl) leads to a completion of this shift, such that an extended Grunwald-Winstein treatment of the specific rates of solvolysis now shows the ionization pathway to be dominant over the full range of solvents.Key words: Grunwald-Winstein equation, solvent nucleophilicity, solvolysis, phenyl chlorothionoformate, phenyl chlorodithioformate.