Copper-zinc species

When 303 was directly treated with Me2Cu(CN)Li2, the transmetallation failed to discriminate between the two carbon-metal bonds. By contrast, the allylzincation of the alkynyllithium derived from the propargylic alcohol 309 produced the alkenyl 1,1-dimetallic species 310, in which the two carbon-metal bonds exhibit different reactivities due to the presence of a metal-alkoxide. Indeed, transmetallation with Me2Cu(CN)Li2 led to the alkenyl copper-zinc species 311, which was relatively poorly reactive towards electrophiles but underwent successful 1,4-addition to ethyl propiolate leading to 312 in satisfactory overall yield (equation 145)180. 

The low-pressure methanol synthesis process utilizes ternary catalysts based on copper, zinc oxide, and another oxide, such as alumina or chromia, prepared by coprecipitation. Cu-Zn0-Al203 and Cu-Zn0-Cr203 are usually the most important industrial catalysts. A significant advance was made when a two-stage precipitation was suggested in which ZnAl2C>4, a crystalline zinc aluminate spinel, was prepared prior to the main precipitation of copper-zinc species.372 This alteration resulted in an increase in catalyst stability for long-term performance with respect to deactivation. Catalyst lifetimes industrially are typically about 2 years. 

Addition of catalytic or stoichiometric quantities of CuCN (TiCl)2 radically increases the reactivity of diorganozinc (R2Zn) and organozinc halide (RZnX) compounds. The resulting copper-zinc species (RCu(CN)ZnR or RCu(CN)ZnX) react with staimyl chlorides (RjSnCl) to give the corresponding alkylated stannyl derivatives (RjSnR)... 

The addition of diorganozinc compounds to alkynes can be promoted by different metallic species snch as Cp2Zrl2 and Ni(acac)2 to give the corresponding vinylic zinc componnds (equation 72). A snbsequent hydrolysis leads to the alkene, whereas iodinolysis provides the vinyl iodide derivative. Copper-zinc species, readily obtained by the... 

The addition of functionalized copper-zinc species, obtained after a transmetallation step between an organozinc halide and an organocuprate, to 1-methylthioalkynes produces... 

In the presence of a Lewis acid, alkyl zinc halides react with aromatic aldehydes to give secondary alcohols. However, alkyl zinc reagents are less reactive than their allyl derivatives and reaction with aliphatic aldehydes is very sluggish. A solution to this is the use (in the presence of aLewis acid) of either the dialkyl zinc reagent or the mixed copper-zinc species RCu(CN)ZnX, formed by transmetaUation of the alkyl... 

Hydroboration (syn addition of H and B) followed by transmetallation with diethyl-or (with secondary boranes) diisopropylzinc provides a useful entry to diorganozinc species. Formation of the copper-zinc species allows reaction with activated electrophiles such as allyl bromide. See A. Bourdier, C. Darcel, F. Flachsmann, L. Micouin, M. Oestreich and P. Knochel, Chem. Ear J., 6 (2000), 2748. 

Deposits. Selenium forms natural compounds with 16 other elements. It is a main constituent of 39 mineral species and a minor component of 37 others, chiefly sulfides. The minerals are finely disseminated and do not form a selenium ore. Because there are no deposits that can be worked for selenium recovery alone, there are no mine reserves. Nevertheless, the 1995 world reserves, chiefly in nonferrous metals sulfide deposits, are ca 70,000 metric tons and total resources are ca 130,000 t (24). The principal resources of the world are in the base metal sulfide deposits that are mined primarily for copper, zinc, nickel, and silver, and to a lesser extent, lead and mercury, where selenium recovery is secondary. 

The elemental and vitamin compositions of some representative yeasts are Hsted in Table 1. The principal carbon and energy sources for yeasts are carbohydrates (usually sugars), alcohols, and organic acids, as weU as a few other specific hydrocarbons. Nitrogen is usually suppHed as ammonia, urea, amino acids or oligopeptides. The main essential mineral elements are phosphoms (suppHed as phosphoric acid), and potassium, with smaller amounts of magnesium and trace amounts of copper, zinc, and iron. These requirements are characteristic of all yeasts. The vitamin requirements, however, differ among species. Eor laboratory and many industrial cultures, a commercial yeast extract contains all the required nutrients (see also Mineral nutrients). 

Blank Tin Iron Zinc Copper Metal Species... 

Mixed copper-zinc reagents also react with alkynes to give alkenylcopper species that can undergo subsequent electrophilic substitution. 

Jeffery J.J., Uren N.C. Copper and zinc species in the soil solution and the effects of soil pH. Aust J Soil Res 1983 21 479M88. 

Transition metal hydroperoxo species are well established as important intermediates in the oxidation of hydrocarbons (8,70,71). As they relate to the active oxygenating reagent in cytochrome P-450 monooxygenase, (porphyrin)M-OOR complexes have come under recent scmtiny because of their importance in the process of (poiphyrin)M=0 formation via 0-0 cleavage processes (72-74). In copper biochemistry, a hydroperoxo copper species has been hypothesized as an important intermediate in the catalytic reaction of the copper monooxygenase, dopamine P-hydroxylase (75,76). A Cu-OOH moiety has also been proposed to be involved in the disproportionation of superoxide mediated by the copper-zinc superoxide dismutase (77-78). Thus, model Cun-OOR complexes may be of... 

Electrophiles, which lead to high yields, are methyl iodide, trialkyltin- and trialkylsUyl chlorides, diphenylphosphinyl chloride, acid chlorides, aldehydes and carbon dioxide. Remarkably, though highly acidic ketones are formed on acylation, no deprotonation or racemization by excess of carbanionic species occurs. Other alkyl halides than methyl iodide react very sluggishly with low yields. Benzylic and aUylic halides lead to partial racemization, presumably due to single-electron transfer (SET) in the alkylation step. As very recently found by Papillon and Taylor, racemization of 42 can be suppressed by copper-zinc-lithium exchange before alkylation to 43 via the Knochel cuprates (equation 7) °. 

A similar technique was used by Soliman, who also used a silica gel matrix and a covalent linker to tie to a series of amines, mono-, di-, tri-, and tetra-amine [15]. Using a batch equilibrium technique, he measured the removal capacities (mmole/g) for divalent forms of cobalt, nickel, copper, zinc, cadmium, and lead. In general maximum removal values (at optimum pH values) were obtained for the tetra-amine species. 

The results of the study are summarized in part in Table 2 and demonstrate two useful consequences. The first result was an effective removal of nuisance transition metal ions 98% removal of zinc ion, 93% removal of nickel(II), 73% removal of copper(II) species. The second result, as a consequence, was the ability to reduce the fresh water intake by recycling reducing water usage by 67%. 

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