KINETICS AND MECHANISM OF THE AMINOLYSIS OF PHENYL DITHIOBENZOATES

The kinetics and mechanism of the reactions of phenyl dithiobenzoates with anilines in acetonitrile at 55.0 degrees C have been studied. The large magnitude of beta(X)(beta(nuc)) and the signs of cross-interact ion constants, rho(XY)(e) > 0, rho(YZ) < 0 and rho(XZ) > 0, are all co nsistent with the carbonyl addition mechanism in which the breakdown o f the tetrahedral intermediate, T-+/-, is rate limiting. The thiocarbo nyl group (drop C=S) is found to favour amine expulsion in contrast to the carbonyl group (drop C=O) which favours the S-bonded nucleofuge e xpulsion from T-+/-. The signs of cross-interaction constants, rho(XY) , rho(XZ) and/or rho(XZ), are shown to provide useful mechanistic crit eria for distinguishing, especially, the carbonyl addition mechanism i nvolving the rate-limiting breakdown of the tetrahedral intermediate ( T-+/-) from the concerted S(N)2 mechanism.