Copper reoxidant

The action of a copper salt converts benzoic acid to phenol. The copper, reoxidized by air, functions as a real catalyst. The Lummus process operates in the vapor phase at approximately 250°C. Phenol yield of 90% is possible ... 

Aldol condensation and subsequent heavies formation are minimized by using a low concentration of the copper reoxidant. 

A similar macromolecular imidazole ligand has also been synthesized and tested in oxidative coupling. The activities are higher compared with low molecular analogs, and this was at least partly due to the enhanced rate of copper reoxidation [96]. 

Seheme 16.38 Palladium (I l)-catalyzed diamination with copper reoxidants... 

CO, and methanol react in the first step in the presence of cobalt carbonyl catalyst and pyridine [110-86-1] to produce methyl pentenoates. A similar second step, but at lower pressure and higher temperature with rhodium catalyst, produces dimethyl adipate [627-93-0]. This is then hydrolyzed to give adipic acid and methanol (135), which is recovered for recycle. Many variations to this basic process exist. Examples are ARCO s palladium/copper-catalyzed oxycarbonylation process (136—138), and Monsanto s palladium and quinone [106-51-4] process, which uses oxygen to reoxidize the by-product... 

SO2 adsorbed on copper oxide bed forming CuSO. Bed is regenerated with H2 or H2—CO mixture giving concentrated SO2 stream. Bed is reduced to Cu, but reoxidized for SO2 adsorption. 

The copper sulfate-pyridine mixture is readily reoxIdized by passing a current of air through it for thirty-six hours (Note 4). To this resulting solution is now added 200 g. of pyridine and it is then used for oxidizing another batch of 1696 g. of benzoin. 

Catalyst regeneration occurs by the reaction of thallium(I) chloride with copper(II) chloride in the presence of oxygen or air. The formed Cu(I) chloride is reoxidized by the action of oxygen in the presence of HCI ... 

In the Lummus process (Figure 10-15), the reaction occurs in the liquid phase at approximately 220-240°C over Mg " + Cu " benzoate. Magnesium benzoate is an initiator, with the Cu " reduced to Cu ". The copper (1) ions are reoxidized to copper (II) ions. 

The concentration dependence of CO oxidation over Pt at (02) (CO) l differs from the concentration dependence of CO oxidation over copper chromite at (02)°-2(C0). This can be explained by the fact that after the departure of a C02 molecule, the reoxidation of platinum surfaces is slow but the reoxidation of base metal oxide surfaces is fast. On the other hand,... 

The carbon monoxide prevents reoxidation of the hot copper. A further temperature rise to about 900°C results in the copper and gold (or silver) at the surface of the parts interacting to form a eutectic. The eutectic melts and runs freely, wetting the surface as well as the attached wires or granules. When the assemblage is finally cooled, the eutectic solidifies, firmly joining the wires or granules to the now decorated surface. 

A very recent addition to the already powerful spectrum of microwave Heck chemistry has been the development of a general procedure for carrying out oxidative Heck couplings, that is, the palladium)11)-catalyzed carbon-carbon coupling of arylboronic acids with alkenes using copper(II) acetate as a reoxidant [25], In a 2003 publication (Scheme 6.6), Larhed and coworkers utilized lithium acetate as a base and the polar and aprotic N,N-dimethylformamide as solvent. The coupling... 

Scheme 6.6 Oxidative Heck coupling of boronic acids and alkenes using copper(ll) acetate as a reoxidant.

Various spectroscopic methods have been used to probe the nature of the copper centers in the members of the blue copper oxidase family of proteins (e.g. see ref. 13). Prior to the X-ray determination of the structure of ascorbate oxidase in 1989, similarities in the EPR and UV-vis absorption spectra for the blue multi-copper oxidases including laccase and ceruloplasmin had been observed [14] and a number of general conclusions made for the copper centers in ceruloplasmin as shown in Table 1 [13,15]. It was known that six copper atoms were nondialyzable and not available to chelation directly by dithiocarbamate and these coppers were assumed to be tightly bound and/or buried in the protein. Two of the coppers have absorbance maxima around 610 nm and these were interpreted as blue type I coppers with cysteine and histidine ligands, and responsible for the pronounced color of the protein. However, they are not equivalent and one of them, thought to be involved in enzymatic activity, is reduced and reoxidized at a faster rate than the second (e.g. see ref. 16). There was general concurrence that there are two type HI... 

Copper is part of several essential enzymes including tyrosinase (melanin production), dopamine beta-hydroxylase (catecholamine production), copper-zinc superoxide dismutase (free radical detoxification), and cytochrome oxidase and ceruloplasmin (iron conversion) (Aaseth and Norseth 1986). All terrestrial animals contain copper as a constituent of cytochrome c oxidase, monophenol oxidase, plasma monoamine oxidase, and copper protein complexes (Schroeder et al. 1966). Excess copper causes a variety of toxic effects, including altered permeability of cellular membranes. The primary target for free cupric ions in the cellular membranes are thiol groups that reduce cupric (Cu+2) to cuprous (Cu+1) upon simultaneous oxidation to disulfides in the membrane. Cuprous ions are reoxidized to Cu+2 in the presence of molecular oxygen molecular oxygen is thereby converted to the toxic superoxide radical O2, which induces lipoperoxidation (Aaseth and Norseth 1986). 

In non-aqueous solution, the copper catalyzed autoxidation of catechol was interpreted in terms of a Cu(I)/Cu(II) redox cycle (34). It was assumed that the formation of a dinuclear copper(II)-catecholate intermediate is followed by an intramolecular two-electron step. The product Cu(I) is quickly reoxidized by dioxygen to Cu(II). A somewhat different model postulated the reversible formation of a substrate-catalyst-dioxy-gen ternary complex for the Mn(II) and Co(II) catalyzed autoxidations in protic media (35). 

Another way to eliminate the oxygen plant is to react a metal oxide with methane to yield the synthesis gas in a fluidized-bed reactor (83-86). Experiments have shown that copper oxide readily oxidizes methane to carbon monoxide and hydrogen with high selectivity at a temperature of about 1200 K and that the reduced CuO can be reoxidized with air. Lewis et al. (83-86)... 

The above considered reactions model the reductive half cycle of GO where a primary alcohol is oxidized to an aldehyde with concomitant reduction of a (phe-noxyl)copper(II) complex to the reduced (phenol)copper(I) species. In the first two cases, reoxidation of the reduced catalyst was achieved by an external oxidant such as tris(4-bromophenyl)aminium or an electrode but not dioxygen. 

In copper electrolysis, there are only a very limited number of impurities that will cause a current efficiency decrease, and these occur particularly in electrowinning. One troublesome impurity is iron, as the ferric ion is preferentially reduced at the cathode to ferrous ion. The ferrous ion is subsequently reoxidized at the anode. The actual current efficiency obtained is dependent on the iron concentration. (8 ) For example, an electrolyte containing 10 gpl iron gives a 77% current efficiency, but with 1 gpl, a 90% value can be obtained. 

The high current intensity associated with the return peak relative to the second reduction process is characteristic of the so-called anodic stripping, which originates from the fast reoxidation of the metallic copper deposited on the electrode surface during the Cu+/Cu° reduction. 

It displays two successive reductions, corresponding to the sequence Cu(II)/Cu(I)/Cu(0). The first step (E° = + 0.19 V) is chemically reversible (ipJipc = 1) but electrochemically quasireversible (A2sp = 145 mV, at 0.2 V s 1) the second step is irreversible ( p = -0.65 V). The appearance of peak C in the backscan reveals, by its characteristic pointed lineshape, the presence of a process known as anodic stripping . This consists of the sudden reoxidation of the metallic copper that has been deposited on the electrode surface during the Cu(I)/Cu(0) reduction. 

In its stoichiometric form, the reaction had been known since the beginning of the 20th century. Direct reoxidation of palladium by oxygen is extremely slow. The invention of Smidt (Wacker Chemie) involved the intermediacy of copper in the re-oxidation of palladium ... 

Nitroso compounds are usually not obtained directly but rather by reoxidation of hydroxylamino compounds or amines. Hydroxylamino compounds are prepared by electrolytic reduction using a lead anode and a copper cathode [573], by zinc in an aqueous solution of ammonium chloride [574 or by aluminum amalgam [147], generally in good yields. 

Carbonylation reactions have been observed using both Pd(II)-alkene complexes and er-bonded Pd(II) species. A catalytic process that includes copper(II) results in concomitant addition of nucleophilic solvent. The copper(II) reoxidizes Pd(0) to the Pd(II) state.144... 

This procedure has been used to prepare a variety of substituted a-bromohydrocinnamic acids 2 p-acetyl-a-bromohydro-cinnamic acid was prepared for the first time by this method. The method illustrates a typical application of the Meerwein reaction for the arylation of unsaturated substrates.3 In this reaction a catalytic amount of a copper(I) salt is used to reduce an aryl diazonium salt forming an aryl radical and a copper(II) halide. Addition of the aryl radical to an unsaturated substrate forms an alkyl radical that is reoxidized by the copper(II) halide present forming an alkyl halide and regenerating the copper(I) salt catalyst. In this preparation, the product, an a-bromo acid, is formed in an acidic reaction mixture and dehydro-halogenation does not occur. However, dehydrohalogenation... 

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