Analytical Sciences

Complex Formation of Copper(II) and Iron(II) with Octadecyloxythiazolylazophenol at the Heptane-Water Interface

Hiroko OYAMA,* Akira OHASHI,** and Hitoshi WATARAI*

*Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
**Department of Environmental Sciences, Faculty of Science, Ibaraki University, Mito 310-8512, Japan

The complex formation of Cu(II) and Fe(II) with a hydrophobic ligand, 5-(octadecyloxy)-2-(2-thiazolylazo)phenol (TARC18), was investigated in the heptane/water system by the high-speed stirring spectrometry and the micro-two phase flow ESI/MS method. At first, the dissociation constant of TARC18 at the heptane/water interface was determined as pK_a = 7.11. The interfacial complexation of the ligand with Cu(II) and Fe(II) under stirred conditions progressed with an increase of the pH. The experimental results showed that a 1:1 complex of Cu(II) and TARC18 was formed at the interface, but was hardly extracted into the heptane phase. On the other hand, the 1:2 complex of Fe(II) with TARC18 formed at the interface was significantly extracted into the heptane phase. The extraction constants and interfacial complex formation constants were estimated for the two systems from the experimental results, and all of the reaction schemes, including the interfacial reactions, were elucidated.

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