Bulletin of the Korean Chemical Society

Korean Chemical Society (대한화학회)
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Electrochemical Behavior of Mordant Red 19 and its Complexes with Light Lanthanides

  • Sang Kwon Lee (Department of Chemistry, Seoul National University) ;
  • Taek Dong Chung (Department of Chemistry, Seoul National University) ;
  • Song-Ju Lee (Department of Chemistry, Chonnam National University) ;
  • Ki-Hyung Chjo (Department of Chemistry, Chonnam National University) ;
  • Young Gu Ha (Department of Chemistry, Seoul National University) ;
  • Ki-Won Cha (Department of Chemistry, Inha University) ;
  • Hasuck Kim (Department of Chemistry, Seoul National University)
  • Published : 1993.10.20
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Abstract

Mordant Red 19(MR19) is reduced at mercury electrode at -0.67 V vs. Ag/AgCl with two electrons per molecule in pH 9.2 buffer by differential pulse polarography and linear sweep voltammetry. The peak potential is dependent on the pH of solution. The exhaustive electrolysis, however, gives 4 electrons per molecule because of the disproportionation of the unstable hydrazo intermediate. The electrochemical reduction of lanthanide-MR19 complexes is observed at more cathodic potential than that of free ligand. The difference in peak potentials between complex and free ligand varies from 75 mV for $La^{3+}$ to 165 mV for $Tb^{3+}$ and increases with increasing the atomic number of lanthanide. The electrochemical reduction of lanthanide complexes with MR19 is due to the reduction of ligand itself, and it can be potentially useful as an indirect method for the determination of lanthanides. The shape of i-E curves and the scan rate dependence indicates the presence of adsorption and the adsorption was confirmed by potential double-step chronocoulometry and the effect of standing time. Also the surface excess of the adsorbed species and diffusion coefficients are determined. The composition of the complex is determined to be 1 : 2 by spectrophotometric and electrochemical methods.

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