Oxidation of Cu

From the reaction of equimolar amounts of CuXj and Cu(Et2C fc)2, XCu(Et2rffc) is formed 135, 99), which can be obtained also by the oxidation of [Cu(Et2rffc)]4 with Xj in stoichiometric quantities 99). A remarkable feature of these complexes is their... 

The reaction features a complex pH dependence which was not resolved. Nevertheless, it was suggested that the variation of the reaction rate as a function of pH was consistent with an additional term in the rate law which was proportional to [HA-]. The kinetic role of [HA-] was interpreted in terms of its reaction with Cu02, which is presumably formed as an intermediate during the autoxidation of Cu(I). In the presence of acetonitrile, Cu(I) can be stabilized as [Cu(MeCN)2]+ and [Cu(MeCN)3]+. As a consequence, the oxidation of Cu(I) becomes rate determining and the overall rate of the catalytic reaction becomes independent of [HA-]. 

The autoxidation of 3,5-di-terf-butylcatechol (H2DTBC) was frequently used to test the catalytic activity of various metal complexes. Speier studied the reaction with [Cu(PY)Cl] (PY = pyridine) in CH2C12 and CHCI3, and reported second-, first- and zeroth-order dependence with respect to Cu(I), 02 and substrate concentrations, respectively (41). The results are consistent with a kinetic model in which the rate determining oxidation of Cu(I) is followed by fast reduction of Cu(II) by H2DTBC. 

In one case pulse-radiolysis techniques were employed to study the effect of pressure on such reactions. The oxidation of [Cu lphenhl by dioxygen proceeds via a Cu1—02 transient in which a copper—oxygen bond is formed, followed by the rapid formation of [Cun(phen)2] and 02 (110). This process is characterized by a AV of 22 cm3 mol1, which is close to the reaction volume expected for the binding of dioxygen. 

Thianthrene radical ion(l+) perchlorate was employed to effect one-electron oxidation of Cu(TPP) (TPP, tetraphenylporphyrinate) to [Cu (Tpp )]+[sbcy (82JA6791). It was also used to dehydrogenate thio-xanthene (44)(R = H), forming perchlorate 43 or, in the presence of an electron-rich aromatic, the 9-Ar-substituted-thioxanthene 44 (R = Ar) (80MI4 82MI4) or, in the presence of a phosphine, phosphonium salts 44 (R = P-"R (81MI7). 

Figure 7.1 (a) Schematic grand potential diagram for oxidation of Cu or Ag and (b) the phase... 

Oxidation of Cu with O2 is markedly slower than the analogous oxidation by TEMPO. The existence of a copper-centered dehydrogenation step was supported by investigating kinetic isotope effects and Hammett correlation studies using different substituted benzyhc alcohols. The /1-hydrogen abstraction was postulated to occur in a concerted mechanism with an -coordinated TEMPO radical bgand (Scheme 4). As such, this TEMPO-mediated copper-catalyzed oxidation of alcohols bears resemblance... 

The Cu3+ or Cu(III) state, 3d8 Copper(III) is isoelectronic with Ni(II) but can not be isolated from aqueous solution. However, several ternary oxides of Cu(III) have been prepared using strongly oxidizing conditions and this oxidation state has been stabilized using a highly basic cation. 

The specific phenomenon in this copper-induced reaction is the configuration of the reduced complex which facilitates the oxidation of Cu(I) to Cu(III). The effect of configuration on the redox behavior of a ligand may be important in interpreting metal-induced enzymatic redox reactions. 

Copper would therefore be expected to form a protective film, be it of copper(I) or copper(II) oxide. (Note, however, that the picture becomes confused where two oxide stoichiometries are involved.) Indeed, oxidation of Cu at 600 to 800 °C proceeds according to the parabolic law ... 

The expansion and contraction of the polymer chain which accompanies the redox of Cu ions can also be visually confirmed by means of the mechanochemical system proposed by Kuhn161), as illustrated in Fig. 31. A film is prepared with a poly(vinylalcohol)-Cu(II) complex and is suspended with a sinker in water. The film is extended by about 20% on the reduction of Cu(II) to Cu(I) and shrinks back to its original length on the oxidation of Cu(I). The poly(vinylalcohol) chain is densely crosslinked by the extremely stable Cu(II) chelate, but is loosened when Cu ion forms the unstable Cu(I) chelate. This change is reversible as may be observed. 

Fig. 9.25. (a) Tafel plots of numerous reactions reduction of benzene, oxidation of Cu in solid electrolyte, reduction of NOj in molten salt, reduction of Fe CNJg,... 

An alternate reduction and oxidation of Cu by superoxide anions Scheme 3) followed from pulse radiolysis experiments value (pH 7.0) of Cu in BESOD... 

Although the oxidation of ethylene to acetaldehyde was known for a number of years,506 its utility depended on the catalytic regeneration of Pd(0) in situ with cop-per(II) chloride discovered by Smidt and coworkers.507 508 Air oxidation of Cu(I) to Cu(n) makes a complete catalytic cycle. This coupled three-step transformation is known as the Wacker process [Eqs. (9.97)-(9.99)]. The overall reaction [Eq. (9.100)] is the indirect oxidation with oxygen of alkenes to carbonyl compounds ... 

At the copper electrode, reduction of Cu2+ is favoured and oxidation of Cu atoms is restricted, so that net cathodic flow occurs. Finally, to prevent a build up of Zn2+ ions near the zinc/electrolyte interface and of SO42-counter ions near the copper, a flux of ions must take place in the electrolytic phase to balance the charge transfer processes at the interfaces. To maintain the flux continuity condition, the applied voltage difference becomes distributed in such a way that ... 

Two types of copper(III) complexes have been isolated. Oxidation of Cu(n-Bu2 Dtc)2 or [Cu(n-Bu2Dtc)] 4 by halogens results in the formation of the diamagnetic square planar monomeric Cu(n-Bu2Dtc)X2 complexes (X = Cl, Br) (33). The crystal structure of Cu(n-Bu2 Dtc)Br2 has been determined (33) (Table LX). 

Unstable copper dioxygen intermediates have been commonly postulated in mechanistic schemes describing the auto-oxidation of Cu(I) complexes or the... 

It has been shown that the process of oxidation of copper in these systems takes place through successive stages. Thus, there is an opinion [617] arguing that a one-electron oxidation of Cu° by a two-component system [for instance, formamide + bipy or DMF(DMSO)+CI4], or a one-electron oxidation of Cu(I) to Cu(ll) by the thiuram (or its dication), or even one-electron oxidation from Cu(II) to Cu(III), for the system DMSO+CI4 + TMTD, all take place with the participation of CI4 or I2 + Me2S I2 as it is formed in the system. 

In relation to the discussed syntheses, we emphasize the systematic study of the kinetics of metal dissolution [202,657-659]. Also, the oxidation of Cu—Zn alloy was studied [658], which opens a route to simple preparation of heteronuclear complexes. 

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