Copper compounds alcohol oxidation

Copper(II) complex 36 is easily reduced to the copper(I) state when an alcohol is present. During this reaction the latter compound is oxidized to an aldehyde. For a series of benzylic alcohols this redox process was studied by UV-vis spectroscopy [39]. The results are presented in Fig. 19 in the form of a Hammett plot. The effect of substituents in the benzene ring on the rate of... 

Oxidation always accompanies nitration, resulting in the formation of nitro compounds and a mixture of acids, aldehydes, ketones, alcohols, nitrites, nitroso compounds, nitroolefins, polymers, carbon monoxide and carbon dioxide. Catalysts such as copper, iron, platinum oxide, etc., accelerate oxidation rather than nitration. 

Copper compounds are catalysts for the Michael addition reaction (249), olefin dimerizations (245, 248), the polymerization of propylene sulfide (142), and the preparation of straight-chain poly phenol ethers by oxidation of 2,6-dimethylphenol in the presence of ethyl- or phenyl-copper (209a). Pentafluorophenylcopper tetramer is an intriguing catalyst for the rearrangement of highly strained polycyclic molecules (116). The copper compound promotes the cleavage of different bonds in 1,2,2-tri-methylbicyclo[1.1.0]butane compared to ruthenium or rhodium complexes. Methylcopper also catalyzes the decomposition of tetramethyllead in alcohol solution (78, 81). 

A number of syntheses of di- and polyacetylenes has been reported. 1-Iodo-l-alkynes couple with terminal acetylenes under palladium-copper catalysis to give 1,3-diynes thus y-iodopropargyl alcohol and phenylacetylene afford compound 30. Oxidative coupling of 1 -alkynes to yield symmetrical 1,3-diynes is brought about by air and copper(I) chloride in the presence of N, A -tetramethylethylenediamine (equation Trialkylsilyl sub-... 

Copper compounds are well known as catalysts that can accelerate the rate of oxidation of several organic compounds in the presence of an oxidizer [48—52]. Also, Cu and Mn have been reported to be concomitant catalysts in the oxidation of several alkanes even at room temperatures [53—56]. These authors report that, although Mn oxides by themselves have been found to be effective in the oxidation of alkanes, the addition of a small concentration of Cu+ ions significantly enhances the conversion of the alkanes to their respective alcohols and aldehydes. 

We have shown, in stoichiometric experiments, that reaction of copper(I) with TEMPO affords a piperidinyloxyl copper(II) complex. Reaction of the latter with a molecule of alcohol afforded the alkoxycopper(II) complex and TEMPOH. Reaction of the alkoxycopper(II) complex with a second molecule of TEMPO gave the carbonyl compound, copper(I), and TEMPOH. This mechanism resembles that proposed for the aerobic oxidation of alcohols catalyzed by the copper-dependent enzyme, galactose oxidase, and mimics thereof. Finally, TEMPOH is reoxidized to TEMPO by oxygen. We have also shown that copper in combination with PIPO affords an active and recyclable catalyst for alcohol oxidation [18]. 

Usually the stable nitroxyl radicals alone cannot directly catalyze the oxidation of alcohols with dioxygen or peroxide, so they rely on the assistance of various cocatalysts that play an important role in activating the oxidation agent. The most used cocatalysts are first row transition-metal complexes where Cu compounds with various N-donor ligands account for the prime ones. In many instances this combination serves as some kind of model to compare catalytic properties of copper compounds. For example, the performances of two asymmetric tetranuclear (with the Cu4(p—0)2(p — 0)2 404 core) and dinuclear (with the Cu2(p-0)2N202 core) copper(II) complexes were compared in the catalytic TEMPO-mediated aerobic oxidation ofbenzylic alcohols. In spite of their similarity, the complexes perform differently the tetranuclear copper(II) (R) complex is highly active leading to yields up to 99% and TONs up to 770, while the (S,R)-2 dinuclear complex is not so efficient under the same conditions. However, no solid explanation of the activity differences was proposed. 

Many cocatalysts are responsible only for electron and proton transfer between the metal catalyst and O2, but examples of cocatalyst interaction with the substrate also exist In the example below, Marko and coworkers have shown that the catalytic use of copper in an aerobic alcohol oxidation is achieved through the catalytic addition of an azo compound [19]. The mechanistic studies support the pathways presented in Scheme 5.4 with a Cu(l)-azo oxidant, 8, in which the azo compound abstracts the hydride from the alcohol, 9. 

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