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Qualitative Identification of Carboxylic Acids, Boronic Acids, and Amines Using Cruciform Fluorophores
Published on: August 19, 2013
Simultaneous spectrophotometric analysis of aliphatic amines utilizing thermochromism of charge-transfer complexes
Tadao Sakai1, Mitsuhiro Kato, Norio Teshima
1Department of Applied Chemistry, Aichi Institute of Technology, 1247 Yachigusa, Yakusa-cho, Toyota 470-0392, Japan. tadsakai@aitech.ac.jp
Abstract:
Aliphatic amines, such as n-hexylamine (primary), di-n-hexylamine (secondary) and tri-n-hexylamine (tertiary amine), react with tetrabromophenolphthalein ethyl ester molecules (TBPEH) to form reddish or red-violet charge-transfer complexes (CT complexes) in 1,2-dichloroethane (DCE). The absorption maxima of the CT complexes with all primary amines occur at around 560 nm, with secondary amines at 570 nm and, with tertiary amines at 580 nm. The CT complex formation constants with TBPEH in DCE increase in the order of the primary, secondary and tertiary amines, but their constants decrease quantitatively with an increase in temperature. This phenomenon (thermochromism) could be applied to the simultaneous spectrophotometric determination of primary amine and secondary amine, or secondary amine and tertiary amine in a mixed solution utilizing the difference of absorbance with temperature changes.
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