Oxidative coupling 2- phenols, silver® oxide

Oxidative coupling of phenols Silver carbonate precipitated on Celite is an excellent reagent for oxidative coupling of phenols thus 2,6-dimethylphenol (1) gives thep-diphenoquinone (2) in 98% yield. 

The stoichiometric oxidative coupling of various phenols proceeds with moderate selectivity (76% ee) in the presence of (-)-sparteine CuCl2, Eq. 106 (127). As mentioned above, selectivity seems to be driven by solubility issues since isolation of the product from the precipitate or from solution results in different enantiose-lectivities. Indeed, this system performs far worse under catalytic conditions. The best result involves the use of silver chloride as reoxidant the heterooxidative coupling of two naphthols 182 and 183 affords the product 184 in 41% yield and 32% ee using 10 mol% catalyst, Eq. 107. 

The formation of o-quinones by the above oxidative methods is less reliable since the ortho quinonoid system is more susceptible to attack by electrophilic and nucleophilic species mild conditions are therefore essential. The use of the silver carbonate/Celite reagent noted above for phenol coupling reactions is particularly suitable the conditions are those described in Expt 6.129, and they have been applied to the oxidation of catechol, 4-methylcatechol, 4-t-butylcatechol, and 3,5-di-t-butylcatechol to yield the corresponding o-quinones in almost quantitative yield. 

One synthesis of cyclopentenone [80], requiring a resolution, involved initial ring contraction of phenol when treated with alkaline hypochlorite (49). Resolution of the resulting cis acid [85] was effected with brucine. The desired enantiomer [86] formed the more soluble brucine salt and was thus obtained from the mother liquors of the initial resolution. Oxidative decarboxylation with lead tetracetate, partial dechlorination with chro-mous chloride, and alcohol protection gave chloro enone [87]. Zinc-silver couple (50) dechlorinated [87] to the desired cyclopentenone [80]. 

Oxidations with sodium persulfate are markedly catalyzed by silver ions the actual reagent is presumed to be SjOg Ag". Toluene is oxidized to benzaldehyde (50% yield) together with coupled products, and benzyl alcohol is oxidized to benzaldehyde (75% yield). Phenols are oxidized to resinous polyphenols. ... 

SCHEME 154. Oxidative phenol coupling reactions with silver carbonate/Celite... 

OXIDATIVE PHENOL COUPLING Ferric chloride. Silver carbonate. Vanadium oxychloride. Vanadium tetrachloride. 

The most important source of acetone is the Hock process for phenol production. In this process acetone is obtained as stoichiometric coupling product. If acetone needs to be produced deliberately, it can be obtained by oxidative dehydrogenation or dehydrogenation of isopropanol. Oxidative dehydrogenation proceeds at 400-600 °C at silver or copper contacts, direct dehydrogenation is carried out at 300-400 °C using zinc contacts. Alternatively, acetone can also be obtained by a Wacker-Hoechst oxidation of propylene. Acetone is used industrially as solvent. Moreover, the aldol condensate products of acetone (diacetone alcohol) are used as solvents. Acetone is also converted in an add catalyzed reaction with two moles of phenol for the synthesis of bisphenol A. Bisphenol A is an important feedstock for the production of epoxy resins and polycarbonates. 

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