チオピラゾロン誘導体の分析化学的研究(第1報) : 1,2,3,4-Substituted-3-pyrazoline-5-thione類ならびにその関連化合物のイオン化定数について

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Protonation equilibrium of a series of 1,2,3,4-tetrasubstituted 3-pyrazoline-5-thiones (I) was examined by spectrophotometry and potentiometric titration. In aqueous solution of sulfuric acid, protonation of the sulfur atom in the thiopyrazolone ring of I occurs and the increase in their ionization rate is greater than the increase of Hammet's acidity function, h_0,by increasing concentration of sulfuric acid. This phenomenon can be explained by the highly polarized structure of I resulting in the different degree of hydration between I and the Hammet indicator. Basicity of I agrees with that presumed from the I-effect of the substituent, and the basicity of 4-substituted thiopyrine derivatives fall in the order of CH_3,H, C_6H_5,I, Br, Cl, NO_2,NH_3^+, and NH(CH_3)_2^+ as a substituent. Ionization constant of thiopyrine is -0.35 and it is a much weaker base than antipyrine.
公益社団法人日本薬学会の論文
1971-03-25