The Copper Effect

An interesting phenomenon in the Stille couplings is the acceleration observed upon the addition of Cu(I) salts [52, 55, 58, 240-245). 

Better results were later obtained using other Cu(I) salts, which allow the reaction to proceed under catalytic conditions [58b, 250-256]. 

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Fig. 1 shows optical density spectra for the copper effective thickness of 1.36 lO g/cm silver effective thickness of 1.67-10 g/sm. The copper monolayer (curve 1) is characterized by the wide LSPA band with maximum at approximately 810 nm. Light attenuation of the copper sample at the spectral range X < 550-600 nm is connected with an interband absorption. 

It is reported in literature that additives like LiCl or Cu(I) salts can have a dramatic influence on the coupling. The copper effect in Stille coupling reactions was investigated by Farina and Liebeskind and coworkers. For instance in the reaction of iodobenzene and vinyltributyltin in dioxane at 50 °C catalyzed by Pd2(dba)3 in presence of a strong ligand like PPhs, it was found that the addition of 2 molar equivalents of Cul per mol of catalyst led to a > 100 fold increase in reaction rate. 

Farina V, Kapadia S, Krishnan B, Wang C, Liebeskind LS. On the nature of the copper effect in the Stille cross-coupling. J. Org. Chem. 1994 59(20) 5905-5911. 

If sulfur is a contaminant, its content can be measured, but it may suffice to characterize its effects by the copper strip corrosion test, or by the doctor test". 

Exciting developments based on electromagnetic induction raced along from that time, giving us the sophisticated products our everyday lives depend on. During most of the period productive uses for eddy current technology were few and few people believed in it as a usefiil tool eddy currents caused power loss in electrical circuits and, due to the skin effect, currents flowed only in the outer surfaces of conductors when the user had paid for all the copper in the cable. The speedometer and the familiar household power meter are examples of everyday uses that we may tend to forget about. The brakes on some models of exercise bicycle are based on the same principle. 

Given that the concentration of both the copper atoms and the electrons m the copper metal will be effectively constant, so that two of the activity tenns can be neglected, we finally have, on rearranging A2.4.107,... 

There are a few documented examples of studies of ligand effects on hydrolysis reactions. Angelici et al." investigated the effect of a number of multidentate ligands on the copper(II) ion-catalysed hydrolysis of coordinated amino acid esters. The equilibrium constant for binding of the ester and the rate constant for the hydrolysis of the resulting complex both decrease in the presence of ligands. Similar conclusions have been reached by Hay and Morris, who studied the effect of ethylenediamine... 

Evans and co-workers investigated the effect of a number of -symmetric bis(oxazoline) ligands on the copper(II)-catalysed Diels-Alder reaction of an N-acyloxazolidinone with cyclopentadiene. Enantiomeric excesses of up to 99% have been reported (Scheme 3.4). Evans et al." suggested transition state assembly 3.7, with a square planar coordination environment around the central copper ion. In this scheme the dienophile should be coordinated predominantly in an cisoid fashion in... 

In contrast, investigation of the effect of ligands on the endo-exo selectivity of the Diels-Alder reaction of 3.8c with 3.9 demonstrated that this selectivity is not significantly influenced by the presence of ligands. The effects of ethylenediamine, 2,2 -bipyridine, 1,10-phenanthroline, glycine, L-tryptophan and L-abrine have been studied. The endo-exo ratio observed for the copper(II)-catalysed reaction in the presence of these ligands never deviated more than 2% from the endo-exo ratio of 93-7 obtained for catalysis by copper aquo ion. 

In this section the catalytic efficiency of Co(DS)2, Ni(DS)2, Cu(DS)2 andZn(DS)2 micelles as well as the effect of CTAB and C12E7 on the copper-ion catalysed Diels-Alder reaction between 5.1 and 5.2 is described... 

In contrast to the situation in the absence of catalytically active Lewis acids, micelles of Cu(DS)2 induce rate enhancements up to a factor 1.8710 compared to the uncatalysed reaction in acetonitrile. These enzyme-like accelerations result from a very efficient complexation of the dienophile to the catalytically active copper ions, both species being concentrated at the micellar surface. Moreover, the higher affinity of 5.2 for Cu(DS)2 compared to SDS and CTAB (Psj = 96 versus 61 and 68, respectively) will diminish the inhibitory effect due to spatial separation of 5.1 and 5.2 as observed for SDS and CTAB. 

The effects of these ligands on the second-order rate constants for the Cu (ligand) catalysed reaction of Ic with 2 are modest In contrast, the effects on IC2 are more pronounced. The aliphatic Oramino acids induce an approximately two-fold reduction of Iv relative to for the Cu" aquo ion. For the square planar coordinated copper ions this effect is expected on the basis of statistics. The bidentate ligands block half the sites on the copper centre. 

In contrast to SDS, CTAB and C12E7, CufDSjz micelles catalyse the Diels-Alder reaction between 1 and 2 with enzyme-like efficiency, leading to rate enhancements up to 1.8-10 compared to the reaction in acetonitrile. This results primarily from the essentially complete complexation off to the copper ions at the micellar surface. Comparison of the partition coefficients of 2 over the water phase and the micellar pseudophase, as derived from kinetic analysis using the pseudophase model, reveals a higher affinity of 2 for Cu(DS)2 than for SDS and CTAB. The inhibitory effect resulting from spatial separation of la-g and 2 is likely to be at least less pronoimced for Cu(DS)2 than for the other surfactants. 

In the first method a secondary acetylenic bromide is warmed in THF with an equivalent amount of copper(I) cyanide. We found that a small amount of anhydrous lithium bromide is necessary to effect solubilization of the copper cyanide. Primary acetylenic bromides, RCECCH Br, under these conditions afford mainly the acetylenic nitriles, RCsCCHjCsN (see Chapter VIII). The aqueous procedure for the allenic nitriles is more attractive, in our opinion, because only a catalytic amount of copper cyanide is required the reaction of the acetylenic bromide with the KClV.CuCN complex is faster than the reaction with KCN. Excellent yields of allenic nitriles can be obtained if the potassium cyanide is added at a moderate rate during the reaction. Excess of KCN has to be avoided, as it causes resinifi-cation of the allenic nitrile. In the case of propargyl bromide 1,1-substitution may also occur, but the propargyl cyanide immediately isomerizes under the influence of the potassium cyanide. 

The rather low value obtained with the copper phthalocyanine, a low-energy solid (line (v)), is probably explicable by some reversible capillary condensation in the crevices of the aggregate, the effect of which would be to increase the uptake at a given relative pressure the plausibility of this explanation is supported by the fact that very low values of s, 1-47-1-77, were obtained with certain other phthalocyanines known to be meso-porous (cf. Chapter 3). 

The superconductor YBa2Cu30g.j, contains copper in both the +2 and +3 oxidation states. Procedures are described for synthesizing the superconductor, demonstrating the superconducting effect, and for determining the amount of Cu + and Cu + in the prepared material. 

When the operating temperature exceeds ca 93°C, the catalytic effects of metals become an important factor in promoting oil oxidation. Inhibitors that reduce this catalytic effect usually react with the surfaces of the metals to form protective coatings (see Metal surface treatments). Typical metal deactivators are the zinc dithiophosphates which also decompose hydroperoxides at temperatures above 93°C. Other metal deactivators include triazole and thiodiazole derivatives. Some copper salts intentionally put into lubricants counteract or reduce the catalytic effect of metals. 

The copper-chelating abihty of sahcylaldoxime has been used to remove copper from brine in a seawater desalination plant effluent. A carbon—sorbate bed produced by sorption of the oxime on carbon proved to be extremely effective in the continuous process (99). In another apphcation, the chelating abihty of sahcylaldoxime with iron and copper was used to stabilize bleaching powders containing inorganic peroxide salts (100). 

The main cause of anode wear is electrochemical oxidation or sulfur attack of anodic surfaces. As copper is not sufficiently resistant to this type of attack, thin caps of oxidation and sulfur-resistant material, such as platinum, are bra2ed to the surface, as shown in Eigure 15a. The thick platinum reinforcement at the upstream corner protects against excessive erosion where Hall effect-induced current concentrations occur, and the interelectrode cap protects the upstream edge from anodic corrosion caused by interelectrode current leakage. The tungsten undedayment protects the copper substrate in case the platinum cladding fails. 

Information on the toxic effects of molybdenum in humans is scarce. A high incidence of gout was reported in a locale in Armenia where the soil contained exceptionally high levels of both molybdenum and copper (15). However, the significance of the suggested correlation is questionable because of the lack of information on the study population and the absence of a control group. 

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