Kinetic and thermodynamic study of the reaction of 2,4,6-triphenylthiopyrylium ion with butylamine and cyclohexylamine in dimethyl sulfoxide

A kinetic and thermodynamic study of the reaction of the 2,4,6-triphenylthiopyrylium ion (1) with butylamine and cyclohexylamine has been performed in Me2SO at 25°C. The reaction involves the initial formation of both the corresponding 2H- and 4H-thiopyrans, which equilibrate to form only the more stable 2H adduct. The kinetic data are consistent with a two-step process wherein the formation of the protonated 2H- and 4H-thiopyran intermediates is the rate-controlling step. A comparison with the addition reaction of 1 with CH3O- shows that the relative stabilities of the 2H and 4H isomers are strongly affected by the charge of the thiopyran derivative. Equilibrium data indicate that the acidity of the ammonium ion is strongly enhanced by the presence of the thiopyranyl moiety. © 1984 American Chemical Society.