Collect. Czech. Chem. Commun.
1991, 56, 2964-2968
https://doi.org/10.1135/cccc19912964
Determination of the substituent constant σp- for the thioamide group -CSNH2 from the ionization of anilines and phenols
Miroslav Polášeka, Karel Waisserb and Tomáš Boučeka
a Department of Analytical Chemistry, Pharmaceutical Faculty, Charles University, 501 65 Hradec Králové
b Department of Inorganic and Organic Chemistry, Pharmaceutical Faculty, Charles University, 501 65 Hradec Králové
Abstract
Thermodynamic ionization constants pKa 2.62 ± 0.01 for the primary aromatic amino group of 4-aminothiobenzamide and pKa 8.28 ± 0.01 for the phenolic hydroxy group of 4-hydroxythiobenzamide have been determined by ultra-violet spectrophotometry at 25°C. By using these pKa values and the Hammett equations (log Ka vs σ) for the ionization of fourteen 3- or 4-substituted phenols and thirteen 3- or 4-substituted anilines the substituent constant σp- = 0.68 (from the ionization of anilines) or σp- = 0.73 (from the ionization of phenols) of the thioamide group -CSNH2 was calculated.
