title: Macroscopic and microscopic ionization constants of the thiol and amine groups in 1-methyl-4-mercaptopiperidine.
abstract: The acid dissociation constants of 1-methyl-4-mercaptopiperidine (pK(1) = 9.51, pK(2) = 11.33), the 1,1-dimethyl-4-mercaptopiperidinium ion (pK(A) = 9.59) and 1-methyl-4-(methylthio)piperidine (pK(B) = 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 (pK(a) = 9.49, pK(b) = 10.23, pK(c) = 11.34, pK(d) = 10.60) have been calculated; pK(A) 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, K(a) + K(b) = K(1), holds very well when it is assumed that the spectrophotometric values for K(a), and K(b), can be replaced by K(A) and K(B) respectively.
authors.affiliation: Departament de Química Inorganica, Universitat Autónoma de Barcelona, Bellaterra, Barcelona, España.
authors.forename: H
authors.initials: H
authors.lastname: Barrera
authors.forename: J C
authors.initials: JC
authors.lastname: Bayon
authors.forename: P
authors.initials: P
authors.lastname: Gonzalez-Duarte
authors.forename: J
authors.initials: J
authors.lastname: Sola
authors.forename: J
authors.initials: J
authors.lastname: Vives