Copper catalysis oxidation

Tinned copper and copper alloys Copper itself has a fair corrosion resistance but traces of copper salts are often troublesome and a tin coating offers a convenient means of preventing their formation. Thus copper wire to receive rubber insulation is tinned to preserve the copper from sulphide tarnish and the rubber from copper-catalysed oxidation, and also to keep the wire easily solderable. Vessels to contain water or foodstuffs, including cooking vessels, water-heaters and heat exchangers, may all be tinned to avoid copper contamination accompanied by possible catalysis of the oxidation of such products as milk, and discolouration in the form of, for example, green stains in water and food. 

The conventional wisdom that one-electron oxidants react with thiols to yield disulfides is apparently derived from reactions in which trace copper catalysis dominated the chemistry. 

A reactive intermediate may be responsible for the copper catalysis of the hydroxylamine reaction. The intermediate formed in the silver-catalyzed reaction, if it has any real existence, is not further oxidized but breaks down into nitrogen and water. Oxidation of hydroxylamine by cupric ion, on the other hand, yields predominately nitrous oxide. The intermediate formed by the removal of a single electron from the hydroxylamine in this reaction must be further oxidized to yield the final product. Such an intermediate may react readily with silver ions in solution. 

Although the preparation has been repeated, there have been no other reports of the type of reaction, (described in 1923) in which carbazole in the presence of excess potassium hydroxide and nitrobenzene at only 50°C gave a good yield of 9-(4-nitrophenyl)-carbazole, presumably via an adduct such as 43 subsequently oxidized by excess nitrobenzene and/or air. More recent examples of N-arylation of carbazoles have involved copper catalysis in reaction of aryl halides with carbazoles. Thus, copper bronze and potassium carbonate heated with the carbazole and the appropriate aromatic halide have produced 9-(4-methoxyphenyl)- and 9-(2-tolyl)carbazoles 9-(4-phenylphenyl)carbazole, l,4-di(carbazol-9-yl)benzene, 4,4 -di(carbazol-9-yl)biphenyl, and 9-(2-pyridyl)- and 9-(2-quinolyl)carbazoles 9-[2-(2-phenylphenyl)phenyl]- and 9-[2-(4-methylphenyl)phenyl] carbazoles 9-(3-bromo-6-nitrophenyl)-, 9-[3-(carbazol-9-yl]-, 9-(2-nitrophenyl)-, 9-(4-methyl-2-nitrophenyl)-, 9-(4-methoxycarbonyl)-l-nitro-, and l-nitro-9-(4-tolyl)carbazoles 9-(2-methoxycarbonylphenyl)carbazole 9-[2- 2-... 

The synthesis of phosphino sulfoximine 97 relied significantly on the successful development of methods pursued in parallel in our group. Whereas palladium-catalyzed cross-couplings between 53 and 98 proceeded in low yield, the copper catalysis with a combination of copper(l) iodide and cesium acetate worked well, affording 99 in up to 83% yield [78]. The resulting phosphine oxides 99 were then reduced to the corresponding phosphines 97 using a mixture of trichlorosilane and triethylamine (Scheme 2.1.1.33). 

Free radicals derived from thiourea have been proposed as intermediates in several oxidations of thiourea. However, the reactions have not yielded much information regarding the identity or thermochemistry of the species implicated. For example, oxidation by IrCl62- occurs with a second-order dependence on [thiourea], a complex pH dependence, and hints of copper catalysis (244). Oxidation by Cu-(me2-phen)2+ is suggested to be an inner-sphere mechanism (92). At this time it is difficult even to guess at the redox potential of the thiourea radical. 

Figures 3 and 4 summarise the catalysis experiments results for the mixed copper-cerium oxide and pristine ceria samples for the NO denox reaction. It can be seen from Figure 3 that the selectivity towards N2 was very high, and for one of the samples higher than for pristine ceria. However, as it can be seen fi om Figure 4 the...

Other authors have also described copper catalysis in the Grignard reaction. In the presence of copper salt, cyclohexene oxide reacts with phenylmagnesium chloride under mild conditions to give tra s-2-phenylcyclohexanol in good yield in the absence of the catalyst, the conversion is low. At the same time, benzylmagnesium chloride led to a yield of 90% even without the catalyst. The reactions between epoxynitriles and Grignard reagents have likewise been studied in detail. ... 

Metal Effects and Prooxidant Action. Ascorbic acid is prooxidant in some situations. Kanner et al. (28) showed that Cu increased the oxidation of linoleate using loss of 8-carotene as an indicator. However, when sufficient ascorbic acid was added to his system, copper catalysis was reversed. Furthermore, when Fe was added, the addition of ascorbic acid increased the prooxidant effect. Previous publications (29) have discussed the deactivation of copper catalysis by ascorbic acid, but in iron-catalyzed oxidation, Fe " initiates oxidation of lipid (2). Fe is formed from Fe by ascorbic acid. Many foods contain metals, and the... 

Hutchings, G.J., Copperthwaite, R.G., Gottschalk, F.M., Hunter, R., Mellor, J., Orchard, S.W., and Sangiorgio, T. A comparative evaluation of cobalt chromium oxide, cobalt manganese oxide, and copper manganese oxide as catalysts for the water-gas shift reaction. Journal of Catalysis, 1992, 137, 408. 

The results of the oxidation of C2—C5 olefins over copper(i) oxide, silver, and gold catalysts are summarized in Table 1. We have excluded data from studies where additives have been deliberately included in the catalyst, or process gas stream, in order to improve the performance. Where several studies have been carried out we have quoted the best selectively obtained. While copper(i) oxide and gold give unsaturated aldehydes as the major product of partial oxidation, silver gives the epoxide. Copperfii) oxide is not a selective catalyst for olefin oxidation. The difference in behaviour between copper(i) and copper(ii) oxides is in line with the general trend in oxide catalysis. The selective catalysts tend to be those with either a full or an empty tZ-shell, i.e. the oxides of Groups IVA, VA, and VIA, and IB, IIB, IVB, VB, and VIB. ... 

Tetrazoles are usually prepared by the reaction of an azide with a nitrile, or an activated amide tri-n-bntyltin azide and trimethylsilyl azide are more convenient and safer reagents than azide anion in some cases copper(I) oxide catalysis in the trimethylsilyl azide protocol is very efficient for the prodnction of A-unsubstituted tetrazoles, " and arylsulfonyl cyanides react with organic azides very efficiently giving rise to 1-substitnted 5-arylsulfonyl-tetrazoles. Zinc bromide can be used to catalyse the reaction between sodinm azide and nitriles in hot water. Intramolecnlar examples involving cyanamides proceed in hot DMF. 3 In additions to nitriles, one can inclnde triethylammoninm chloride (instead of ammoninm chloride)... 

Hansen et al. [269] found that copper is an active catalyst for the oxidation of polypropylene. In the presence of copper, the autocatalytic period is completely absent and the oxidation itself is then catalysed. The experiments suggest that cuprous oxide is responsible for the catalysis and not metallic copper. Cuprous oxide is considerably more active as a catalyst than cupric oxide or freshly reduced copper. A similar result was obtained by Meltzer et al. [415]. 

Effects of a series of transition metal stearates, the concentration of the copper stearate, the solvent, various additives, and other factors on the thermal oxidation of polypropylene were studied in trichlorobenzene solution. The mechanism of copper catalysis is discussed. The order of decreasing catalytic activity of the metal stearates was Cu > Mn > Fe > Cr > Al Ni Co control Ti >> Zn >> V. The addition of propionic acid to the solvent accelerated the oxidation of the polymer. The presence of the copper leveled off oxygen uptake of the polymer after a certain time. The amount of oxygen absorbed decreased with increasing concentration of the copper, and at higher concentration (7.9 X 10 3M) the polymer oxidation was inhibited. 

In this chapter, the effect of a series of transition metal stearates on the thermal oxidation of polypropylene in homogeneous solution is examined, and the results obtained are compared with that in bulk reported previously (16). In addition, the effects of the anion of copper compounds, the concentration of copper, the solvent, and the additives on the copper compound-catalyzed thermal oxidation of polypropylene are studied, and the mechanism of the copper catalysis in solution is discussed. 

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