Oxidation copper-catalysed

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. 

This polymer, prepared by copper catalysed air oxidation of dipropynyl carbonate, exploded readily on warming or manipulation. The corresponding adipate and sebacate esters are non-explosive. The authors wonder if peroxide formation is involved such explanation seems otiose. 

Breuer, P. L. Jeffrey, M. I. Copper catalysed oxidation of thiosulfate by oxygen in gold leach solutions. Miner. Eng. 2003, 16, 21-30. 

Figure 6.17. Fluorinated macrocycles used for the cobalt or copper catalysed oxidation of saturated or...

This specification is for butter oil, which is butter with the water removed. The free fatty acid limit is to detect lipolytic rancidity while peroxide value specification is to limit oxidative rancidity. The copper limit arises because copper catalyses the oxidation of fats. The absence of neutralising substances is to prevent a high titration for free fatty acids being covered up by the addition of alkali. 

Phenylcyclobutanone has been a substrate for a copper-catalysed Baeyer-Villiger oxidation. Thus the complex (35), (ca 1 mole%) in conjunction with... 

Bis-oxazoline ligands can also be produced by oxidative coupling of the copper derivative of diastereoisomerically pure 306 (Scheme 145) . Further lithiations of the product 317, which was produced as single diastereoisomer, occur (as in Scheme 143) at the second site adjacent to the oxazoline, giving, for example, 318, despite the (presumably) less favourable stereochemistry of the lithiation step. Bisoxazolines 318 direct the asymmetric copper-catalysed cyclopropanation of styrene using diazoacetate. 

The aryl chloride is formed when the diazonium-copper(i) chloride complex decomposes by a radical mechanism summarised below. Copper catalyses this decomposition because it can undergo interconversion between the +1 and + 2 oxidation states as a result of electron transfer. 

Corey chose a Wittig-style (HWE) reaction to control the aldol process and copper-catalysed addition of vinyl Grignard for the conjugate addition. Oxidation with NaI04 and catalytic OSO4 gave the keto-aldehyde 35 which cyclised cleanly under equilibrating conditions. 

Copper-Catalysed Aerobic Oxidation of Alcohols Using DEAD H2... 

Forss, D.A., Angelini, P., Bazinet, M.L., Merritt, C. 1967. Volatile compounds produced by copper-catalysed oxidation of butterfat. J. Am. Oil. Chem. Soc. 44, 141-143. 

Iron and copper catalyse the formation of oxyradicals. Three reactions are relevant in this context (1) Autoxidation of metal complexes may yield the superoxide radical which by itself is not very reactive, but is a precursor of more reactive radical species. (2) The one-electron reduction of hydrogen peroxide -the Fenton reaction - results in hydroxyl radicals via a higher oxidation state of iron [2]. (3) A similar reaction with organic peroxides leads to alkoxyl radicals, although a recent report alleges that hydroxyl radicals are also formed [3]. There is a fourth radical, the formation of which does not require mediation by a metal complex. This is the alkyldioxyl radical, ROO , which is formed at a... 

Toluene has been oxidized by the silver ion catalysed reaction with peroxy-disulfate. The reaction produces a mixture of bibenzyl, benzaldehyde and benzoic acids.299 Russian workers have described the conversion of 4-methoxy-toluene to the benzaldehyde by oxidation with peroxydisulfate in the presence of silver or copper ions and oxalic acid.300 The presence of copper salts in iron or copper catalysed peroxydisulfate oxidation is believed to suppress side-reactions.301 Phillips have patented a palladium(II)/tin(IV)/persulfate system for the oxidation of toluene derivatives.302 The reactions are carried out in carboxylic acid solvents (Figure 3.78). 

The utility of microwaves in the copper catalysed protocol for N-arylation using high molecular weight poly(ethylene glycol) (PEG 3400) as a solvent was explored by Colacino et al. [17] for accessing the N-arylated benzimidazole (vi) in presence of cuprous oxide, cesium carbonate and PEG 3400 under microwave activation, with no supplementary ligands. 

A copper catalysed click (azide-alkyne cycloaddition) reaction has been used to prepare a fluorous-tagged TEMPO catalyst (Figure 7.20). TEMPO is a stable organic free radical that can be used in a range of processes. In this case, its use in metal-free catalytic oxidation of primary alcohols to aldehydes using bleach as the terminal oxidant was demonstrated. The modified TEMPO can be sequestered at the end of the reaction on silica gel 60 and then released using ethyl acetate for reuse in further reactions in this way the TEMPO was used four times with no loss in activity. 

PS has also been used in the copper catalysed aerobic oxidation of primary alcohols (Scheme 9.3). The selective oxidation of primary alcohols into aldehydes can be complicated by overoxidation to carboxylic acids or even decomposition products. These side reactions were not observed in PS, and a high turnover frequency (>31 h ) was achieved. The product could be easily isolated by extraction into -pentane and the PS catalyst-containing phase could be recycled three times. 

In contrast to silver-catalysed cumene oxidation, the evidence concerning the mechanism of copper-catalysed reactions favours radical initiation via surface hydroperoxide decomposition. Gorokhovatsky has shown that the rate of ethyl benzene oxidation responds to changes in the amount of copper(ii) oxide catalyst used, in a manner which is characteristic of this mechanism. Allara and Roberts have studied the oxidation of hexadecane over copper catalysts treated in various ways to produce different surface oxide species, Depending on the catalyst surface area and surface oxide species present, a certain critical hydroperoxide concentration was necessary in order to produce a catalytic reaction. At lower hydroperoxide levels, the reaction was inhibited by the oxidized copper surface. XPS surface analysis of the copper catalysts showed a... 

The oxidative coupling uses a copper-catalysed system and a base, usually an aliphatic or heterocyclic amine, and oxygen as the oxidizing agent. In broad terms, free-radical processes are involved to explain the polymerization pathway which involves formation of the phenoxide radical, and coupling of two radicals through the attack by an oxygen-centred radical at the para position of another phenolic molecule (Scheme 25). 

Hagenmaier [158] studied the catalytic effect of metals, oxides and carbonates on the decomposition of chloroaromatics such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofuranes. Copper catalyses dechlorination/hydrogenation of these compounds at temperatures of about 553 K. After heating for 15 minutes the amount of most polychlorinated compoimds was below 0.1 ng. 

The number of S- and N-arylations with arylbismuth reagents is relatively limited. The reaction of thiols with pentavalent organobismuth reagents leads mostly to oxidation products and, in some instances, to 5-phenylation. In the case of the nitrogen derivatives, the most efficient arylation by arylbismuth reagents are reactions which are copper-catalysed, and these will be reviewed in a later part of this chapter (see section 6.7). 

In this section we describe INS studies of molybdenum trioxide, a precmsor of molybdenum disulfide catalysts ( 7.5), and transition metal oxides which catalyse complete or partial oxidation of hydrocarbons, and copper zinc oxide catalysts, which catalyse methanol synthesis from carbon monoxide and dihydrogen ( 7.3.3). 

Oxidation.— Two copper-catalysed reactions have been described for the degradation of the 22-aldehyde (298) to give a pregnan-20-one (299). Oxygenation of a solution of the aldehyde with the copper(n) acetate-2,2 -bipyridyl complex and diazabicyclo-octane in dimethylformamide gave the 20-ketone in 90% yield. A free-radical mechanism is proposed (Scheme 14). 

On the development of copper-catalysed olefin aziridination, Evans et al. [36] reported oxidative amidine formation. Treatment of cyclohexene, a less reactive substrate towards... 

The most significant application of the C5-unit 73 (Scheme 7) is in the BASF process for the production of vitamin A [22]. Industrial syntheses of 73 [23] proceed via but-l-ene-3,4-diol diacetate (74) by acetylation and copper-catalysed rearrangement of 75. A new route is emerging via the vinyloxirane 76, which has recently become accessible via silver-catalysed gas-phase oxidation [24]. The diacetate 74 is formed as a byproduct in the oxidative acetoxylation of butadiene (14), which is performed on an industrial scale to produce butane-1,4-diol (77) [25]. 

Fig. 11.10 The protective action of cobalt upon the copper-catalysed oxidation (by O2) of cysteine (m/40) (20°C). A, m/10000 cupric sulfate B, M/100000 cupric sulfate C, as B, but with m/500 cobaltous sulfate. (Baur and Preis, 1936.)...

The traditional approach has been to accept that flavonoids retard the copper-catalysed oxidation of ascorbic acid by chelating with copper and possibly other trace elements. Harper, Morton and Rolfe have shown that the protective mechanism is possibly more complex than this they found that flavonoids exerted a strong protective action under conditions where EDTA (a potent inhibitor of copper-catalysed ascorbic aci oxidation) was ineffective [67]. As an alternative and possibly complementary mechanism, they suggested that the protective capacity is derived from the ability of flavonoids to act as free radical acceptors free radical formation is believed to be an important phase of ascorbic acid oxidation [67]. It should be noted, however, that the model system used for these studies was designed primarily to elucidate the mechanism of ascorbic acid protection by flavonoid in fruit juices at a low pH it would be improper, without qualification, to extrapolate them to physiological conditions of pH, temperature and concentration. 

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