Equilibrium and kinetics of proton transfer from thiocarboxylic acids to γ-collidine

NMR and IR spectroscopy have been used in studying the equilibrium in the reaction of proton transfer from thiocarboxylic acids RCOSH R=CH₃ (a), C₆H₅ (b) or CH₂Cl (c)] to -collidine (d), and also the kinetics of CH/NH proton exchange between protonated -collidine and excess RCOSH. For compoundsa and b, partial protonation of the -collidine is observed; and for compound c, complete protonation. The heat of reaction of proton transfer with the participation of binary acidamine associates is 30 (a) and 45 (b) kJ/mole. The rate of proton exchange decreases and the activation energy E increases with increasing acidity of the RCOSH E=44 (b) and 88 (c) kJ/mole] and with increasing basicity of the amine (E_d < E_TEA), which, in accordance with the orders of reaction that were found for the exchanged components, is due to a mechanism in which the slow stage is proton transfer in the ion pair NH⁺...^–SOCR. The thiocarboxylate ion of c is unstable; and after splitting out Cl^–, it forms the compounds Cl(CH₂COS)₂ ^– and (CH₂COS)₂.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 2, pp. 187–194, March–April, 1985.