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Investigation of 8-mercaptoquinoline (thiooxine) and its derivatives .110. Physicochemical properties of 5-amino-8-mercaptoquinoline

D. Zaruma, M. Cirule, I. Zuika, Z. Brüvers, M. Zikmund, and Ya. Bankovskii

Institute of Inorganic Chemistry, Academy of Sciences of the Latvian SSR, SU+229 021 Salaspils


Abstract: Some physicochemical properties of 5-amino-8-mercaptoquinoline and 5-amino-8-methylmercaptoquinoline are described: electronic absorption spectra have been studied and molar absorption coefficients of ionized, protonated, thiolic and zwitterionic forms of 5-amino-8-mercaptoquinoline, of neutral and protonated form of 5-amino-8-methylmercaptoquinoline in aqueous solutions, as well as of thiolic and zwitterionic form of 5-amino-8-mer- captoquinoline and neutral form of 5-amino-8-methylmercaptoquinoline in organic solvents have been determined. In polar solvents 5-amino-8-mercapto- quinoline exists in considerable concentrations as the zwitterionic form and its concentration increases with the increase of dielectric permeability of the solvent. Cumulation ionization constants have been determined and individual ionization constants of 5-amino-8-mercaptoquinoline have been calculated. It follows from the latter that amino group in the 5th position of quinoline ring considerably increases the basic properties of the heterocyclic nitrogen atom (pK B = 4.74) and slightly diminishes the acidic properties of mercapto group (pK D = 7.44) when compared to those of 8-mercaptoquinoline (pK B = 3.50, pK D = 7.01). This fact can be ascribed to the electron-donor effect. It may be concluded from the values of protonation constants of the heterocyclic nitrogen SCHi SCHi atom (pKm+ — 4.74) and primary amino group (рКмн3+ = 0.50) of 5-ami- no-8-methylmercaptoquinoline that for addition of a proton to the primary amino group considerably higher acidity than for addition of a proton to the heterocyclic nitrogen atom is necessary. Solubility of 5-amino-8-mercaptoquinoline in water,, dependence of extrac­ tion into organic solvents on hydrogen ion concentration in aqueous phase, two-phase ionization constant in the system chloroform—water (рКг = 8.85) and distribution constant between chloroform and water ( X D = 1.4) have been determined spectrophotometrically.

Full paper in Portable Document Format: 393a329.pdf


Chemical Papers 39 (3) 329–344 (1985)

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