Cu selectivity

A feature common to a number of receptors showing good Cu selectivity is the presence of one or more primary... 

Ocypa, M. Michalska, A. Maksymiuk, K. Accumulation of Cu(II) cations in poly(3,4-ethylenediox54hiophene) films doped by hexacyanoferrate anions and its application in Cu +-selective electrodes with PVC based membranes. Electrochim. Acta 2006, 51, 2298-2305. 

Cp RhCl2]2/Cu(0Ac)2H20 catalyst system in place of the Pd/Cu selectively gives a diaUcenylation/nudeophilic cycUzation product (path B) [12]. 

The reaction is cis-steieospecific when esters of acetic acid are used while, in the case of a-bromopropionic esters, a mixture of cis-trans aziridines is formed. The cu-selectivity shown by esters of acetic acid is not surprising. In fact, it may be explained by assuming an E geometry for both the enolate and the imine and a closed chair-like Zimmerman-Traxler transition state in which the imine side chain is in an axial position while the halogen atom is in an equatorial location. The subsequent nucleophilic di lacement oi the halogen atom in the resulting intermediate teads directly to the formation of the cis-aziridine (Scheme 19). 

The lead-free solder whose composition is nominally 95.5Sn-3.9Ag-0.6Cu will be the focus of the analysis. The material property information presented should be appropriate for slight deviations from this composition. For simplicity, the alloy will be referred to as Sn-Ag-Cu. Select comparisons will be made with standard eutectic lead-tin solder with 2%Ag (62Sn-36Pb-2Ag). For convenience, the lead-tin eutectic material with 2%Ag will be designated as Sn-Pb. 

It also demonstrated chromogenic behavior and turned from colorless to deep purple red, which allowed naked-eye detection of ions. A rhodamine derivative 32 [109] as well as salicylaldehyde fluorescein hydrazine 33 represents a Cu " "-selective fluorescent chemosensor [110]. 

Chen S J, Sanz F, Ogletree D F, Hallmark V M, Devine T M and Salmeron M 1993 Selective dissolution of copper from Au-rich Au-Cu alloys an electrochemical STS study Surf. Sc . 292 289... 

Table 2,8, Solvent effect on the endo-exo selectivity (% endo -% exo) of the nncatalysed and Cu" -ion catalysed Diels-Alder reaction between 2,4c and 2,5 at 25°C.

Table 2.10. Substituent effect on the selectivity of the Cu catalysed reaction of 2.4 with 2.5 in water at25°C.

Finally the influence of the temperature and addition of ethanol on the enantioselectivity of the Diels-Alder reaction was studied. Table 3.3 summarises the results for different aqueous media. Apparently, changes in temperature as well as the presence of varying amounts of ethanol have only a modest influence on the selectivity of the Cu(tryptophan)-catalysed Diels-Alder reaction in aqueous solution. However, reaction times tend to increase significantly at lower temperatures. Also increasing the alcohol content induces an increase of the reaction times. 

Oxidative carbonylation of alcohols with PdCh affords the carbonate 572 and oxalate 573(512-514]. The selectivity of the mono- and dicarbonylation depends on the CO pressure and reaction conditions. In order to make the reaction catalytic, Cu(II) and Fe(III) salts are used. Under these conditions, water is formed and orthoformate is added in order to trap the water. Di-/-butyl peroxide is also used for catalytic oxidative carbonylation to give carbonates and oxalates in the presence of 2,6-dimetliylpyridine(515]. 

Appendix 3D contains a listing of the standard-state reduction potentials for selected species. The more positive the standard-state reduction potential, the more favorable the reduction reaction will be under standard-state conditions. Thus, under standard-state conditions, the reduction of Cu + to Cu E° = -1-0.3419) is more favorable than the reduction of Zn + to Zn (E° = -0.7618). 

Sketch the spectrophotometric titration curve for the titration of a mixture of 5.00 X 10 M Bi + and 5.00 X 10 M Cu + with 0.0100 M EDTA. Assume that only the Cu +-EDTA complex absorbs at the selected wavelength. 

Membranes fashioned from a mixture of Ag2S with CdS, CuS, or PbS are used to make ion-selective electrodes that respond to the concentration of Cd +, Cu +, or Pb +. In this case the cell potential is... 

Selecting a Constant Potential In controlled-potential coulometry, the potential is selected so that the desired oxidation or reduction reaction goes to completion without interference from redox reactions involving other components of the sample matrix. To see how an appropriate potential for the working electrode is selected, let s develop a constant-potential coulometric method for Cu + based on its reduction to copper metal at a Pt cathode working electrode. 

The macrocychc hexaimine stmcture of Figure 19a forms a homodinuclear cryptate with Cu(I) (122), whereas crown ether boron receptors (Fig. 19b) have been appHed for the simultaneous and selective recognition of complementary cation—anion species such as potassium and fluoride (123) or ammonium and alkoxide ions (124) to yield a heterodinuclear complex (120). 

Activators enhance the adsorption of collectors, eg, Ca " in the fatty acid flotation of siUcates at high pH or Cu " in the flotation of sphalerite, ZnS, by sulfohydryl collectors. Depressants, on the other hand, have the opposite effect they hinder the flotation of certain minerals, thus improving selectivity. For example, high pH as well as high sulfide ion concentrations can hinder the flotation of sulfide minerals such as galena (PbS) in the presence of xanthates (ROCSS ). Hence, for a given fixed collector concentration there is a fixed critical pH that defines the transition between flotation and no flotation. This is the basis of the Barsky relationship which can be expressed as [X ]j[OH ] = constant, where [A ] is the xanthate ion concentration in the pulp and [Oi/ ] is the hydroxyl ion concentration indicated by the pH. Similar relationships can be written for sulfide ion, cyanide, or thiocyanate, which act as typical depressants in sulfide flotation systems. 

Sta.rting from Phenol. Phenol can be selectively oxidized into -benzoquinone with oxygen. The reaction is catalyzed by cuprous chloride. At low catalyst concentration, the principal drawback of this method is the high pressure of oxygen that is required, leading to difficult safety procedures. It appears that a high concentration of the catalyst (50% of Cu(I)—phenol) allows the reaction to proceed at atmospheric pressure (58). 

Other Methods. A variety of other methods have been studied, including phenol hydroxylation by N2O with HZSM-5 as catalyst (69), selective access to resorcinol from 5-methyloxohexanoate in the presence of Pd/C (70), cyclotrimerization of carbon monoxide and ethylene to form hydroquinone in the presence of rhodium catalysts (71), the electrochemical oxidation of benzene to hydroquinone and -benzoquinone (72), the air oxidation of phenol to catechol in the presence of a stoichiometric CuCl and Cu(0) catalyst (73), and the isomerization of dihydroxybenzenes on HZSM-5 catalysts (74). 

Copper is an attractive metallisation element because of its high conductivity. It has been added to Al in low concentrations (AlSi(l%)—Cu(0.5%)) to improve conductive priorities. Selective, low temperature copper CVD processing, using copper(I) P-diketonate compounds, has been carried out (23). 

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