Cation-Anion Combination Reactions. 21. Reactions of Thiolate Ions, Cyanide Ion, and Amines with Cations and Carbonyl Compounds in Me2SO Solution

Article abstract of DOI:10.1021/ja00376a041

The pK_a's of three alkanethiols and of two ammonium ions, and the rates of reactions of the thiolates, amines, and of cyanide ion with Malachite Green, Crystal Violet, 2,4-dinitrophenyl acetate, and 9-acetyl-9-cyanofluorene, all in Me2SO solution, have been measured.The pK_a's of the thiols in Me2SO, compared with those in water, indicate important hydrogen bonding of water to the thiolates.The reactions of nucleophiles with both the triarylmethyl cations and 2,4-dinitrophenyl acetate have rate constants that are greater in Me2SO than in water.The solvent effects on rates are compared with solvent effects on equilibrium constants to arrive at measures of the progress of the transition states toward products as "seen" by solvent.These measures are not in accord with other measures, such as Broensted slopes, possibly indicating that transition states are not solvated in a manner suggested by stable molecule analogues.The pattern of nucleophilic reactivities toward 9-acetyl-9-cyanofluorene is different from that toward 2,4-dinitrophenyl acetate.A possible rationalization involving concerted reactions of 2,4-dinitrophenyl acetate, but stepwise reactions of the ketone, is discussed.