ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Investigation of 8-mercaptoquinoline (thiooxine) and its derivatives .115. Spectral and acid-base properties of phenyl derivatives of 8-mercaptoquinoline

J. Ashaks, G. Jansons, Y. Bankovskii, and M. Zikmund

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

Abstract: Two new derivatives of 8-mercaptoquinoline have been synthesized: 5-phenyl- and 6-phenyl-8-mercaptoquinoline. Their electronic absorption spectra have been studied and ionization as well as distribution constants have been determined. At ionic strength 1 = 0.1 mol dm^-3 and temperature 0 = 2O°C for 5-phenyl-8-mercaptoquinoline the values pK_i = 1.97 and pK₂ = 8.41 have been found, for 6-phenyl-8-mercaptoquinoline pKi = 2.01 and pK₂ = 8.19 (the values found previously for 2-phenyl- and 4-phenyl-8-mercaptoquinoline were pK_i = 1.41, pK₂ = 8.00 and pK_i, = 2.10, pK₂ = 8.49, respectively). In the system chloroform—water at ionic strength 1 = 0.1 mol dm^-3 and temperature 0 = = 20 °C the following distribution constants have been determined: for 5-phenyl-8-mercaptoquinoline 60 000 and for 6-phenyl-8-mercaptoquinoline 70 800 (the previously found values for 2-phenyl- and 4-phenyl-8-mercaptoquinoline were 470 000 and 78 000 respectively). The comparison with the previously investigated 8-mercaptoquinoline, 2-phenyl-, and 4-phenyl-8-mercaptoquinoline is drawn. It is shown that phenyl group in the 4th and 5th position to a large extent affects the p band of л—> л * electron transition while in the 2nd and 6th position it affects the ß band of  л—>л* electron transition causing the bathochromic and hyperchromic shift. Phenyl group in the 5th and 6th position in the molecule of 8-mercapto­quinoline decreases to some degree the basic properties of nitrogen atom and increases acidic properties of mercapto group, but in the 4th position it slightly increases basic properties of nitrogen atom and decreases acidic properties of mercapto group. In the 2nd position phenyl group considerably decreases basic properties of nitrogen atom and slightly decreases acidic properties of mercap­ to group; the latter fact can be explained by steric effects of this group.

Full paper in Portable Document Format: 395a667.pdf

Chemical Papers 39 (5) 667–686 (1985)