Copper redox system

In order to avoid such an undesirable effect drying agents, such as ethylortho-formate or boric anhydride 01 the calcined sodium form of a synthetic zeolite, can he added to the reaction mixture (21 ]. Moreover the negative influence of water on the activity and productivity of the catalytic system is also related to (he deactivation of the copper redox system. Indeed, in dr> alcohol, the real copper oxidant species is titc alkoxide Cu(OK)CI which is readily formed via the reaction ... 

A system based on a copper redox system [55] is a combined electrolytic and catalytic process carried out in a three-compartment cell. The cell consists of a central packed bed anode of graphite separated by an ion exchange membrane from a packed cathode bed of copper on one side, and on the other side a packed bed of Cu which acts as an absorber. In the absorption chamber the copper, after first being oxidised to cuprous oxide, is responsible for the oxidation of SO2 to sulphuric acid. 

Insoluble 3-methylPT with incorporated copper(II)salt arising from CuCl2 used during chemical polymerization as co-promoter pressed as pellets has been used as both anode and cathode of a very stable battery cell with 0.1M aqueous sodium perchlorate solution with perchloric acid as supporting electrolyte at pH 1.5. The charge-discharge process has an efficiency of 0.31, but it is unknown if the charge capacity is within the copper redox system or within the PT redox system [99]. 

The action of redox metal promoters with MEKP appears to be highly specific. Cobalt salts appear to be a unique component of commercial redox systems, although vanadium appears to provide similar activity with MEKP. Cobalt activity can be supplemented by potassium and 2inc naphthenates in systems requiring low cured resin color lithium and lead naphthenates also act in a similar role. Quaternary ammonium salts (14) and tertiary amines accelerate the reaction rate of redox catalyst systems. The tertiary amines form beneficial complexes with the cobalt promoters, faciUtating the transition to the lower oxidation state. Copper naphthenate exerts a unique influence over cure rate in redox systems and is used widely to delay cure and reduce exotherm development during the cross-linking reaction. 

Although sulfonyl chlorides add readily to unactivated olefins, with vinylic monomers telomeric and/or polymeric products were observed. This difficulty has been overcome by carrying out the addition in the presence of catalytic amounts of CuCl2, so as to provide a general and convenient synthesis of /5-chlorosulfones (Asscher-Vofsi reaction)63. For the copper-catalyzed system a redox-transfer mechanism has been suggested in which the... 

If the zinc- and copper-containing portions of this redox system are physically separated, electron transfer can occur only through an external wire. 

A typical inorganic redox system of this type involves the equilibrium between metallic copper and copper(II) ions. In the absence of a complex-former the disproportionation constant is large and a solution of Cu+ ions is very unstable. However, in the presence of ammonia, copper(I) ions are bonded in a complex, constant K decreases and the -j8 curve exhibits three inflection points. 

Theoretical calculations have been carried out on a number of zinc-containing enzymatic systems. For example, calculations on the mechanism of the Cu/Zn enzyme show the importance of the full protein environment to get an accurate description of the copper redox process, i.e., including the electronic effects of the zinc ion.989 Transition structures at the active site of carbonic anhydrase have been the subject of ab initio calculations, in particular [ZnOHC02]+, [ZnHC03H20]+, and [Zn(NH3)3HC03]+.990... 

The blue, or type 1, copper proteins, azurin from Pseudomonas aeruginosa (Adman et ai, 1978 Adman and Jensen, 1981) and from Al-caligenes denitrificans (Norris et al., 1983, 1986) and poplar plastocyanin (Guss and Freeman, 1983 Guss et al., 1986), have been studied by X-ray diffraction. These involve a Cu(I)/Cu(II) redox system. Cu(I) d ) is... 

The cyclic voltammetry behavior of the Cu(II) rotaxane, 4(5)2+ (Fig. 14.8b), is very different from that of 4, t l +. The potential sweep for the measurement was started at - 0.9 V, a potential at which no electron transfer should occur, regardless of the nature of the surrounding of the central Cu(II) center (penta- or tetracoordinate). Curve i shows two cathodic peaks a very small one, located at + 0.53 V, followed by an intense one at —0.13V. Only one anodic peak at 0.59 V appears during the reverse sweep. If a second scan ii follows immediately the first one i, the intensity of the cathodic peak at 0.53 V increases noticeably. The main cathodic peak at —0.15 V is characteristic of pentacoordinate Cu(II). Thus, in 4(5)2+ prepared from the free rotaxane by metalation with Cu(II) ions, the central metal is coordinated to the terdentate terpyridine of the wheel and to the bidentate dpp of the axle. On the other hand, the irreversibility of this peak means that the pentacoordinate Cu(I) species formed in the diffusion layer when sweeping cathodically is transformed very rapidly and in any case before the electrode potential becomes again more anodic than the potential of the pentacoordinate Cu2 + /Cu+ redox system. The irreversible character of the wave at —0.15 V and the appearance of an anodic peak at the value of + 0.53 V indicate that the transient species, formed by reduction of 4(5)2 +, has undergone a complete reorganization, which leads to a tetracoordinate copper rotaxane. The second scan ii, which follows immediately the first one i, confirms this assertion. 

Blumberg, W. E. et at Is trivalent copper a viable oxidation state in the enzymic turnover of copper proteins In Oxidases and Related Redox Systems (King, T. E., Mason, H. S., Morrison, M., eds.), Oxford-New York, Pergamon Press, 1981... 

By contrast, the cobalt and iron doped electrodes form a perfectly reversible redox system showing voltammograms which are independent of film thickness. It was suggested that differences arose from more facile electron hopping in the case of four coordinate copper(II) than for five or six coordinate M11/111 (M = Co, Fe). Electrodes doped with manganese(II) or zinc(II) gave no response. 

Some redox systems have been developed for certain polymers. The copper/iodine system is well established for polyamide thermal stabilization, and in spite of introducing a heavy metal ion into the polymer, works well in an oxygen-free environment.83 84... 

Corrosion inhibitor - corrosion inhibitors are chemicals which are added to the electrolyte or a gas phase (gas phase inhibitors) which slow down the - kinetics of the corrosion process. Both partial reactions of the corrosion process may be inhibited, the anodic metal dissolution and/or the cathodic reduction of a redox-system [i]. In many cases organic chemicals or compounds after their reaction in solution are adsorbed at the metal surface and block the reactive centers. They may also form layers with metal cations, thus growing a protective film at the surface like anodic oxide films in case of passivity. Benzo-triazole is an example for the inhibition of copper cor-... 

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