Cobalt catalysis phenol oxidation

The role of Coball-dioxygen complexes in autooxidations other than phenol oxidation is less certain, and ostensibly similar reactions appear to follow radically different pathways. Thus, in the oxidation of thiols to disulfide catalyzed by Co11 species catalysis by the phthalocyanine complex [Con(TSPc)]4 apparently proceeds via a Co1 intermediate and without participation of Co—02 species,680 whereas catalysis by [CoH(TPP)] appears to involve initial formation of an >/ cobalt-dioxygen complex from which Of is displaced by thiolate.681 Several reviews giving extensive coverage to oxidations catalyzed by cobalt(II) complexes are available.649,650,682 683... 

An example of a kinetic study of a coordinated ligand reaction at ruthen-ium(III) is provided by that of hydrolysis of p-nitrophenylacetate catalyzed by [Ru(NH3)5(im)] . This complex is a very effective catalyst, being 10,000 times more effective than its cobalt(III) equivalent.Acetylacetone exchange at [Ru(acac)3] will be discussed under cobalt(III) (see Section 5.7.5.2). The rate law for ruthenium trichloride catalysis of oxidation of (substituted) phenols by periodate in alkaline aqueous solution is claimed to indicate preequilibrium formation of a ruthenium(III)-phenol complex. This is assumed to arise from re action between the phenol and RuOHaq present in aqueous solutions of ruthenium trichloride.The substitution reaction... 

Nevertheless, the application of alkoxy-functionalized 1,3-dienes is of increasing interest. 1-Alkoxy-functionalized 1,3-butadienes led directly to arene derivatives such as 22 via the cycloaddition/elimination route (Scheme 13.12) [13]. The arene is formed under the reaction conditions of cobalt catalysis upon elimination of trimethyl-silanol from the labile dihydroaromatic intermediate. When 2-alkoxy-functionalized 1,3-butadienes are employed, 3,4-disubstituted phenol derivatives such as 23 are readily available by DDQ oxidation of the dihydroaromatic intermediate. The DDQ oxidation conditions led in several cases to direct desilylation of the enol ether or the desilylation takes place during column chromatography on (nondeactivated) silica gel. 

Sippola, V. O. and Krause, A. O. I., Oxidation activity and stability of homogeneous cobalt-sulphosalen catalyst -Studies with a phenolic and a non-phenolic lignin model compound in aqueous alkaline medium. J Molecular Catalysis A-Chemical 2003, 194 (1-2), 89-97. 

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