Kinetics and Mechanism of the Benzenethiolysis of <i>O</i>-Ethyl<i> S</i>-(2,4-Dinitrophenyl) and <i>O</i>-Ethyl <i>S</i>-(2,4,6-Trinitrophenyl) Dithiocarbonates and <i>O</i>-Methyl <i>O</i>-(2,4-Dinitrophenyl) Thiocarbonate
作者:Enrique A. Castro、Paulina Pavez、José G. Santos
DOI:10.1021/jo0352530
日期:2003.11.1
Reactions of O-ethyl2,4-dinitrophenyldithiocarbonate (EDNPDTC), O-ethyl 2,4,6-trinitrophenyl dithiocarbonate (ETNPDTC), and O-methyl O-(2,4-dinitrophenyl) thiocarbonate (MDNPTOC) with a series of benzenethiolate anions in aqueous solution, at 25.0 degrees C and an ionic strength of 0.2 M (KCl), are subjected to a kinetic investigation. Under excess benzenethiolate, these reactions obey pseudo-first-order
The reactions of pyrrolidine with O-ethyl S-(X-phenyl) dithiocarbonates (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 ethanol, 25.0 degrees C, and ionic strength 0.2 M (maintained with KCl). Pseudo-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-type plot (log k(N) vs. pK(a) for the leaving group) is linear with slope beta(lg) = -0.2, which is consistent with a mechanism through a tetrahedral 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 reactions 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 piperidine rather than pyrrolidine. (C) 1997 John Wiley & Sons, Inc.