KINETICS AND MECHANISM OF THE AMINOLYSIS OF O-ETHYL S-ARYL DITHIOCARBONATES IN ACETONITRILE

The aminolysis reactions of O-ethyl S-(Z-phenyl) dithiocarbonates (Z = p-CH3, H p-Cl, and p-NO2) with anilines (AN) and N,N-dimethylanilines (DMA) in acetonitrile at 30.0 degrees C are investigated. Relatively small values of beta(X) (beta(nuc),0.4 ca. 0.7) and beta(Z) (beta(lg) -0.1 ca. -0.4) for both ANs and DMAs, significantly large k(H)/k(D) va lues (1.1 ca. 1.9) involving deuterated anilines, and large negative r ho(XZ) values for ANs (-0.56) are interpreted to indicate a concerted mechanism for both ANs and DMAs but with a hydrogen bonded four-center type transition state (TS) for ANs. The relative leaving ability, k(Z = p-NO2)/k(Z = p-CH3), is smaller for ANs than for DMAs, especially f or a weaker nucleophile (1.9 and 4.7 for AN and DMA, respectively, wit h X = p-Cl), This suggests that the rate enhancement by the hydrogen-b ond formation in the four-center type TS for AN is greater for a weake r nucleofuge (Z = p-CH3), especially when the nucleophile (X = p-Cl) i s weaker. (C) 1998 John Wiley & Sons, Inc.