The acid dissociation constants of 1-methyl-4-mercaptopiperidine (pK1 = 9.51, pK2 = 11.33), the 1,1-dimethyl-4-mercaptopiperidinium ion (pKA = 9.59) and 1-methyl-4-(methylthio)piperidine (pKB = 10.18) have been determined potentiometrically in 3M sodium perchlorate (10% methanol) medium. The ultraviolet absorption of the mercaptide ion has been used to determine the relative proton affinity of the sulphur and nitrogen functions in 1-methyl-4-mercaptopiperidine under the same conditions, and its four microscopic constants (pKa = 9.49, pKb = 10.23, pKc = 11.34, pKd = 10.60) have been calculated; pKA has also been determined spectrophotometrically. From the results obtained, it can be concluded that the thiol group is more acidic than the amine group and that the Adams relation, Ka + Kb = K1, holds very well when it is assumed that the spectrophotometric values for Ka, and Kb, can be replaced by KA and KB respectively. © 1983.
|Publication status||Published - 1 Jan 1983|