- Autoxidation of Phenols Catalyzed by Copper(II)-Ethylenediamine Complexes: The Reaction Mechanism
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The mechanism of the autoxidation of phenols with molecular oxygen catalyzed by Cu(II)-ethylenediamine complexes is elucidated.The kinetics are of first order in both and and of one-half order in .Those results imply the formation of a oxygen-bridged complex in the course of the reaction.The C-C coupling of two phenoxy radicals is facilitated within the coordination sphere of Cu(II) and affords the primary oxidation products, i. e. 2,2'-biphenyldiols.The bulkiness of substituents determines the type of the secondary products and either benzofuran or dioxepin is produced.Taking into account the results of oxidation of 2,2'-biphenyldiols, the mechanism of the production of benzofuran and dioxepin is also clarified.In the Cu(II) complex with sterically crowded biphenyldiolate, the oxidation activity of Cu(II) has been enhanced and the coordinating biphenyldiolate is immediately oxidized to benzofuran.On the contrary, the biphenyldiolate-Cu(II) complex with square-planar geometry could not produce benzofuran.After the complex is forced into the active tetrahedral configuration by the access of phenoxy radical-Cu(II) complex, the biphenyldiolate is oxidized to biphenyloxy radical and suffers C-O coupling with the phenoxy radical to afford dioxepin.
- Kushioka, Keiko
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p. 4456 - 4459
(2007/10/02)
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- Catalytic Activity of Copper(II)-Ethylenediamine Complexes in Autoxidation of Phenols
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Studies of the autoxidation of tert-butylphenols 1-4 with molecular oxygen in the presence of Cu(II) complexes of N-substituted ethylenediamines indicate that the most catalytically active complexes are sterically crowded around the nitrogen atoms.The principal primary oxidation products formed in the presence of these complexes are substituted biphenyls 5, 7, 10, and 14, the first three of which are converted into secondary products on prolonged oxidation.Only in the oxidation of 2 is a diphenyl ether (9) formed, in quantities that increase little after the first 5 min of oxidation.
- Kushioka, Keiko
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p. 4948 - 4950
(2007/10/02)
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- Oxidative Coupling of Phenols. Part 10. The Role of Steric Effects in the Formation of C-O Coupled Products
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The formation of C-O coupled products in the oxidative coupling of phenols is hindered by bulky ortho-substituents in the aryloxyl radical intermediates as shown by the predominant formation of the ortho-ortho-C-C coupling products in the oxidation of o-t-butyl- and 2,4-di-t-butyl-phenol. 3,5-Di-t-butyl-phenol gives exclusively the ortho-O-dimeric product as steric effects prevent the sandwich approach of two aryloxyl radicals necessary for C-C coupling.
- Armstrong, David R.,Cameron, Colin.,Nonhebel, Derek C.,Perkins, Peter G.
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p. 587 - 590
(2007/10/02)
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