Aerobic oxidation of 2,3,6-trimethylphenol to trimethyl-1,4-benzoquinone with copper(II) chloride as catalyst in ionic liquid and structure of the active species
| Autor: | Joerg Sundermeyer, Hongjian Sun, Klaus Harms |
|---|---|
| Rok vydání: | 2004 |
| Předmět: |
chemistry.chemical_classification
Inorganic chemistry Molecular Conformation chemistry.chemical_element General Chemistry Electron acceptor Crystallography X-Ray Biochemistry Copper Catalysis 1 4-Benzoquinone chemistry.chemical_compound Colloid and Surface Chemistry chemistry Triplet oxygen Phenols Polymer chemistry Ionic liquid Copper(II) chloride Benzoquinones Copper chloride Oxidation-Reduction |
| Zdroj: | Journal of the American Chemical Society. 126(31) |
| ISSN: | 0002-7863 |
| Popis: | TMQ is an important precursor in industrial vitamin E synthesis. We report a "green chemistry approach" with respect to the highly selective and environmentally friendly oxidation of 2,3,6-trimethylphenol (TMP) to trimethyl-1,4-benzoquinone (TMQ) with molecular oxygen as oxidant and a copper catalyst immobilized in a molten salt. n-Butanol as co-solvent has a positive effect on the activity and selectivity. The structurally characterized catalyst, a 1-n-butyl-3-methylimidazolium oxotetracuprat, is formed in situ via hydrolysis of CuCl2 in the presence of imidazolium chloride. We propose a mechanism of oxidative phenolate activation at a [Cu4(mu4-O)]6+ core as electronically coupled electron acceptor, formation of a copper-bound phenolate radical anion, spin delocalization into the aromatic ring, and attack by triplet oxygen at the para position. Attack of Cu(I) as reduction equivalent at the peroxy radical, proton-mediated elimination of a copper(II)-hydroxo species, will either substitute a copper(I) site in the reduced oxo cluster or take up an electron from the reduced mixed valent cluster [Cu4(mu4-O)]6+ to regenerate the oxidized cluster as the active electron acceptor. |
| Databáze: | OpenAIRE |
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