Concerted mechanism of the aminolysis of 2,4,6‐trinitrophenyl o‐ethyl dithiocarbonate in aqueous ethanol

The reactions of the title substrate with a series of secondary alicyclic amines are subjected to a kinetic study in 44 wt% aqueous ethanol, 25.0°C, and ionic strength 0.2 M (KCl). The Brönsted‐type plot (log k N vs. p K a of the amine, where k N is the second‐order rate coefficient) obtained is linear with slope β = 0.53, which indicates a concerted mechanism. The predicted Brönsted break for a hypothetical stepwise mechanism is p K   a 0= 8.7, which was not observed (p K a range of amines: 6–11). The same reaction in water is stepwise, which shows that the tetrahedral intermediate found in water is much destabilized by the change of solvent from water to aqueous ethanol. © 1994 John Wiley & Sons, Inc.