非水溶液における呈色反応(第4報) : Bromophenol Blue とジメチルアミン誘導体の反応における置換基効果

概要

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Examination was made on the substituent effect on the color reaction of bromophenol blue (H_2A) with tertiary amines (B) in benzene and ethyl acetate. Eleven kinds of dimethylamine derivatives Me_3N-R (R=metyl, ethyl, propyl, iso-propyl, benzyl, etc.) were used and equilibrium constants, ΔH and ΔS in equation (2), were determined. H_2A+B⇌BH^+・HA^- K_1=[BH^+・HA^-]/[H_2A]・[B] BH^+・HA+B⇌BH^+(BH^+・A^<2->) K_2=[BH^+(BH^+・A^<2->)]/[BH^+・HA^-]・[B] Comparison of the δ_Rlog K_2 (difference of the logarithmic equilibrium constants between trimethylamine and each amine) with Taft's σ^* value indicates that δ_Rlog K_2 reflects the polar substituent effect to some extent. As may be seen from ΔH-ΔS diagram, the additional steric effect of the methyl group introduced into α-carbon increases the entropy and influences the reaction. This reaction is an enthalpy-entropy controlled reaction.
公益社団法人日本薬学会の論文
1971-12-25