CONCERTED MECHANISM OF THE AMINOLYSIS OF 2,4,6-TRINITROPHENYL O-ETHYLDITHIOCARBONATE IN AQUEOUS-ETHANOL

The reactions of the title substrate with a series of secondary alicyc lic amines are subjected to a kinetic study in 44 wt% aqueous ethanol, 25.0-degrees-C, and ionic strength 0.2 M (KCl). The Bronsted-type plo t (log k(N) vs. pK(a) of the amine, where k(N) is the second-order rat e coefficient) obtained is linear with slope beta = 0.53, which indica tes a concerted mechanism. The predicted Bronsted break for a hypothet ical stepwise mechanism is pK(a)o = 8.7, which was not observed (pK(a) range of amines: 6-11). The same reaction in water is stepwise, which shows that the tetrahedral intermediate found in water is much destab ilized by the change of solvent from water to aqueous ethanol. (C) 199 4 John Wiley & Sons, Inc.