On In Situ Prepared Cu–Phenanthroline Complexes in Aqueous Alkaline Solutions and Their Use in the Catalytic Oxidation of Veratryl Alcohol
✍ Scribed by Heikki Korpi; Paweł J. Figiel; Elina Lankinen; Paul Ryan; Markku Leskelä; Timo Repo
- Publisher
- John Wiley and Sons
- Year
- 2007
- Tongue
- English
- Weight
- 170 KB
- Volume
- 2007
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
The in situ prepared complex based on copper(II) sulfate and 1,10‐phenanthroline (phen) and its performance in the catalytic oxidation of veratryl alcohol (3,4‐dimethoxybenzyl alcohol) to veratraldehyde with O~2~ in alkaline aqueous solutions have been studied. In aqueous solution, the structure of Cu–phen complexes varies with reaction conditions; by changing either the copper‐to‐ligand molar ratio or the pH, the amount of coordinated 1,10‐phenanthroline and hydroxido ligands in the coordination sphere of copper can be altered in a controlled manner. The highest activities are achieved in the pH range 12.6–13.3, which correlates with the presence of the [Cu(phen)(OH)~2~] species according to complex distribution curves. According to the UV/Vis and EPR studies, the oxidation reaction is initiated by the reduction of [Cu(phen)(OH)~2~] to Cu^I^ species by veratryl alcohol, which can be seen as a disappearance of the Cu^2+^ EPR signal and as a shift of the UV/Vis absorbance maximum from about 690 nm to the 410 and 525 nm regions. When molecular oxygen is added, the Cu^I^ species is readily oxidised back to Cu^II^ species, and the catalytic formation of aldehyde is initiated. On the basis of these observations, a mechanism for the catalytic oxidation is proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)