非水溶液における呈色反応(第5報)ベンゼン中におけるBromophenol Blueによる第三級アミン類の光度滴定

抄録

Photometric titration of tertiary amines was examined with Bromophenol Blue (I) as a titrant in benzene. This method depends on the fact that an increase in absorbance at 410 mμ is proportional to the concentration of amines according to equation (1) if I is present in greater concentration than the amine. H₂A+B⇄BH⁺·HA^- [BH⁺·HA^-]/[H₂A][B]=K₁ (1) BH⁺HA^-+B⇄BH⁺(BH⁺·A^2-) [BH⁺(BH⁺·A^2-)]/[BH⁺·HA^-][B]=K₂ (2) where H₂A is I, B is amine, BH⁺HA^- and BH^-(BH⁺·A^2-) are (1 : 1) and (1 : 2) compounds, respectively. The effect of (1 : 2) compound on the titration curve was discussed, and the limit of equilibrium constant K₁ and the concentration of amine determined. Next, this method was applied to the determination of drugs (amine type) such as chloropromazine hydrochloride, diphenhydramine hydrochloride, etc. These studies led to the conclusion that a minute quantity of amines in benzene (2×10^-6M solution) can be easily and accurately determined with 0.0002M of I as a titrant by means of photometric titration if K₁ between I and amines is greater than 10⁷ (pK₂=8).