The reactions of O ‐(4‐nitrophenyl) S ‐aryl dithiocarbonates with anilines: Effects on the relative nucleofugality

Kinetic and high‐performance liquid chromatography studies were investigated for the reactions of S ‐phenyl, S ‐(4‐chlorophenyl), and S ‐(4‐nitrophenyl) O ‐(4‐nitrophenyl) dithiocarbonates with anilines. These were performed in the presence of 0.1M borate buffer in 44 wt% aqueous ethanol. For reactions of the 3 substrates, the mechanism is stepwise with 2 tetrahedral intermediates, one zwitterionic (T ± ), and the other anionic (T − ), where the intermediate T − is formed by proton transfer from T ± to the borate buffer. The nonleaving group is not passive, playing an important role in the relative nucleofugality of the groups, which depend largely on its electron withdrawing capability. The nucleofugacity of 4‐nitrophenolate ion and of 4‐nitrophenylthiolate from the same tetrahedral intermediate is similar, despite the differences in their basicities (3 p K a units). In the reactions of S ‐(4‐nitrophenyl) O ‐(4‐nitrophenyl) dithiocarbonate, the change of nucleophile from pyridines (only 4‐nitrophenolate ion is nucleofuge) to anilines (2 nucleofuges) shows that the nature of the amine impacts on the relative nucleofugality of groups.