Oxygen coupling mixture

The anodic coupling of aryl ethers is reviewed in Ref. [180]. Aryl ethers are more selectively coupled than phenols for the following reasons The carbon-oxygen coupling is made impossible and the ortho-coupling and the oxidation to quinones become more difficult. A mixture of triflu-oroacetic acid (TFA) and dichloromethane proved to be the most suitable electrolyte [181]. TFA enhances the radical cation stability and suppresses the nucle-ophilicity of water. Of further advantage is the addition of alumina or trifluo-roacetic anhydride [182]. Table 12 compiles representative examples of the aryl ether coupling. 

In the case of oxidation of phenols, the reaction can very quickly give a complex mixture of products. This is because the phenoxy radical formed on abstraction of the hydrogen radical, H can give rise to carbon-carbon, carbon-oxygen and oxygen-oxygen coupling reactions. 

The reduction of a diastereomeric mixture of enantiomerically pure /3-keto sulfoxides (7) furnished one of the four possible isomers with good overall stereoselectivity (90%), when carried out under conditions which favor epimerization of the a chiral center (eq 16). This outcome derives from a chelation-controlled reduction (involving the sulfoxide oxygen) coupled with a kinetic resolution of the two diastereoisomers of (7). ... 

Scheme 8.16. The results of oxidation of phenol by basic iron(III) cyanide. Ferricyanide is thought to oxidize the phenol to the corresponding radical, and coupling reactions of the radical with itself at electron-rich sites followed by proton tautomerism produce the product mixture shown. The peroxide, resulting from oxygen-oxygen coupling, is not obtained nor is it expected to be stable under the reaction conditions.

Thallium benzoate can be used as a catalyst in the oxidation of all l aromatic compounds by oxygen/air mixtures. A couple of alkyl aromatic... 

The Fischer-Tropsch reaction is essentially that of Eq. XVIII-54 and is of great importance partly by itself and also as part of a coupled set of processes whereby steam or oxygen plus coal or coke is transformed into methane, olefins, alcohols, and gasolines. The first step is to produce a mixture of CO and H2 (called water-gas or synthesis gas ) by the high-temperature treatment of coal or coke with steam. The water-gas shift reaction CO + H2O = CO2 + H2 is then used to adjust the CO/H2 ratio for the feed to the Fischer-Tropsch or synthesis reactor. This last process was disclosed in 1913 and was extensively developed around 1925 by Fischer and Tropsch [268]. 

A closer analysis of die equilibrium products of the 1 1 mixture of methane and steam shows the presence of hydrocarbons as minor constituents. Experimental results for die coupling reaction show that the yield of hydrocarbons is dependent on the redox properties of the oxide catalyst, and the oxygen potential of the gas phase, as well as die temperamre and total pressure. In any substantial oxygen mole fraction in the gas, the predominant reaction is the formation of CO and the coupling reaction is a minor one. 

In a reaction similar to 12-50, azoxy compounds can be prepared by the condensation of a nitroso compound with a hydroxylamine. The position of the oxygen in the final product is determined by the nature of the R groups, not by which R groups came from which starting compound. Both R and R can be alkyl or aryl, but when two different aryl groups are involved, mixtures of azoxy compounds (ArNONAr, ArNONAr, and Ar NONAr ) are obtained and the unsymmetrical product (ArNONAr ) is likely to be formed in the smallest amount. This behavior is probably caused by an equilibration between the starting compounds prior to the actual reaction (ArNO -I- Ar NHOH Ar NO - - ArNHOH). The mechanism has been investigated in the presence of base. Under these conditions both reactants are converted to radical anions, which couple ... 

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