The kinetics and mechanism of the aminolysis of aryl proanedithioates with
benzylamines are investigated in acetonitrile at -35.0 degreesC. A large ma
gnitude of the Hammett (rho (X) and rho (Z)) and Bronsted (beta (X) and bet
a (Z)) coefficients and exceptionally large cross-interaction constant rho
(XZ)(=3.5) are consistent with a stepwise mechanism in which leaving group
expulsion from an intermediate, T+/-, is the rate-determining step. The fas
ter rates observed for dithio esters (II) than for thio esters (I), and the
validity of the reactivity-selectivity principle (RSP) are also in line wi
th the mechanism proposed. The k(H)/k(D) values (=1.0-1.8) determined with
deuterated benzylamines (XC6H4CH2ND2) and the activation parameters, DeltaH
(similar or equal to8 kcal mol(-1)) and DeltaS(not equal)(=-16 to -23 e.u.)
, suggest that proton transfer occurs concurrently with leaving group depar
ture in the transition state.