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KMID : 1059519890330010055
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Journal of the Korean Chemical Society
1989 Volume.33 No. 1 p.55 ~ p.64
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Reduction and Equilibrium of Vanadium-Diethylenetriamine Pentaacetates at Mercury Electrode in Aqueous Solution
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Jung Ki-Suk
Sohn Se-Chul
Ha Young-Kyung
Eom Tae-Yoon
Yun Sock-Sung
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Abstract
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Reduction and equilibrium of vanadium-DTPA (DTPA = diethylenetriaminepentaacetic acid, H5A) complexes at mercury electrodes are studied in 0.5M NaClO4 aqueous solution at 3.2 < pH < 10.5 and 25℃. At 3.2 < pH < 5.9, the reduction reaction is V·A2- + H+ + e- = V·HA2-, while at 5.9 < pH < 10.5 it is V·A2- + e- = V·A3-. The stability constants of V·HA2- and V·A3- are found to be 6.46 × 109 and 3.09 × 1014, respectively. V(Ⅳ)-DTPA undergoes stepwise complexation as VO2+ + H2A3- = VO·HA2- + H+ and VO·HA2- = VO·A3- + H+, where acidity constant of VO·HA2- is pKa = 7.15. Stability constants of VO·HA2- and VO·A3- are found to be 1.41 × 1014 and 3.80 × 1017, respectively. It is detected that VO2+-DTPA is reduced irreversibly to V·A2- with the transfer coefficient of α = 0.43. At more cathodic overpotential, the reduction is stepwise as V(Ⅳ)→V(Ⅲ)→V(Ⅱ). The first one corresponds to VO·HA2- + e- → VO·HA3- at 3.2 < pH < 7.2 and VO·A3- + e- → VO·A4- at 7.2 < pH < 10.5. The second is identical to that of V(Ⅲ). Diffusion coefficients of VO·HA2- and VO·A3- are found to be (9.0±0.3) × 10-6 cm2/s and (5.9±0.4) × 10-6 cm2/sec, respectively.
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KEYWORD
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