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On In Situ Prepared Cu–Phenanthroline Complexes in Aqueous Alkaline Solutions and Their Use in the Catalytic Oxidation of Veratryl Alcohol
Author(s) -
Korpi Heikki,
Figiel Paweł J.,
Lankinen Elina,
Ryan Paul,
Leskelä Markku,
Repo Timo
Publication year - 2007
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200600908
Subject(s) - chemistry , aqueous solution , catalysis , copper , alcohol oxidation , alcohol , aldehyde , inorganic chemistry , electron paramagnetic resonance , ligand (biochemistry) , absorbance , coordination sphere , phenanthroline , metal , organic chemistry , biochemistry , physics , chromatography , receptor , nuclear magnetic resonance
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)