A kinetic study of the oxidation of 2-(2-hydroxyethyl)pyridine by chromium(VI) in strongly acidic aqueous solutions of HClO4 |
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Authors: | Kita Ewa Pietkiewicz Aleksandra |
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Institution: | (1) Department of Chemistry, N. Copernicus University, 87-100 Toru , Poland |
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Abstract: | Oxidation of 2-(2-hydroxyethyl)pyridine (pyeol) to 2-pyridylacetaldehyde (pyeal) by CrVI has been studied in the 0.5–2.0 M HClO4 range at I = 2.2 M and in super acidic media within the 3–7 M HClO4 range. In all cases the reaction has been examined under pseudo-first order conditions keeping the alcohol and H+
aq in excess. CrIII-complexes formed during reduction of CrVI by pyeol at different molar ratios of the reactants, were isolated chromatographically and identified as Cr(H2O)6]3+ and Cr(pyeac)(H2O)4]2+ ions (pyeac = 2-pyridylacetic acid). Free 2-pyridylacetaldehyde (pyeal) was separated and determined as its 2,4-dinitro-phenylhydrazone derivative. A dependence of the rate constants on pyeol] and H+] has been established at I = 1.2 M and I = 2.2 M. The apparent activation parameters at H+] = 1 and 2 M have been determined. A rate law of the form dCrVI]/dt= (k
1H
+]+k
2H
+]2)pyeol]CrVI] is proposed. A linear dependence of log k
obs on H0 in the super acidic media is obeyed. A rate decrease is observed if oxygen instead of argon is in the reaction cell. The reaction mechanism has been discussed. |
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