Mechanism of sulfur transfer from 1,2,4- dithiazolidine-3,5-diones to triphenylphosphines

摘要

The mechanism of sulfurization of substituted triphenylphosphines with 4-(3- and 4-substituted)-1,2,4- dithiazolidine-3,5-diones in acetonitrile, dichloromethane, tetrahydrofuran and toluene at 25 °C was studied. The reaction pathway involves rate-limiting initial nucleophilic attack of the phosphorus at sulfur followed by fast decomposition of the phosphonium intermediate to the corresponding phosphine sulfide, phenylisocyanate and carbonylsulfide. From the Hammett correlations and from the solvent dependency, it was concluded that the transition-state structure is very polar and resembles the zwitter-ionic intermediate. The extent of P-S bond formation and S-S bond cleavage is very similar in the solvents series, but the latter gradually decreases with the decreasing polarity of the solvent.