Mechanistic study on the substitution reactions of O ‐ethyl S ‐aryl dithiocarbonates with quinuclidines

The quinuclidinolysis of 4‐nitrophenyl, 2,4‐dinitrophenyl and 2,4,6‐trinitrophenyl O ‐ethyl dithiocarbonates ( 1 , 2 , and 3 , respectively) are studied kinetically at 25.0 °C, ionic strength 0.2 M; the two former in water and the latter in 44 wt% ethanol–water. The Brønsted plots (log k N vs. p K a of quinuclidinium ions) for the reactions of 1 and 2 are linear with slopes β  = 0.94 and 0.76, respectively, and that of 3 shows a smooth curvature. From these results and other arguments it can be concluded that the quinuclidinolysis of dithiocarbonate 1 in water is stepwise, in contrast to those of dithiocarbonates 2 in water and 3 in aqueous ethanol, which are concerted. The kinetics and mechanistic effects of the leaving and electrophilic groups and the amine nature are discussed. Copyright © 2008 John Wiley & Sons, Ltd.