STRUCTURE-REACTIVITY CORRELATION IN THE REACTIONS OF PYRROLIDINE WITHO-ETHYL S-ARYL DITHIOCARBONATES IN AQUEOUS-ETHANOL

The reactions of pyrrolidine with O-ethyl S-(X-phenyl) dithiocarbonate s (X = 4-methyl, 4-methoxy, H, 4-chloro, 4-nitro, 2,4-dinitro, and 2,4 ,6-trinitro) are subjected to a kinetic study in 44 wt% aqueous ethano l, 25.0 degrees C, and ionic strength 0.2 M (maintained with KCl). Pse udo-first-order kinetics are found under amine excess. Linear plots of the pseudo-first-order rate coefficient against concentration of free -base pyrrolidine are obtained for all the reactions, the nucleophilic rate coefficient (it,) being the slope of such plots. The Bronsted-ty pe plot (log k(N) vs. pK(a) for the leaving group) is linear with slop e beta(lg) = -0.2, which is consistent with a mechanism through a tetr ahedral intermediate (T-+/-) where its formation is rate determining. The beta(lg) Value is very similar to that found in the same reactions in water. There is a great difference in the mechanism of the reactio ns of O-ethyl S-phenyl dithiocarbonate with pyrrolidine (order one in amine) and piperidine (complex order in amine) in aqueous ethanol, and this is attributed to a greater nucleofugality from T-+/- of piperidi ne rather than pyrrolidine. (C) 1997 John Wiley & Sons, Inc.