Copper II halide

Alkoxybenzenes were highly regioselectively halogenated by use of copper(II) halides supported on alumina to give 4-halo-alkoxybenzenes in high yield. Bromination of alkoxybenzenes with alumina-supported copper(II) bromide occurred at lower temperature than chlorination with alumina-supported copper(II) chloride (ref. 14). 

The yield increased with increasing the ratio of alumina-supported copper(II) bromide to alkoxybenzenes. The size of alkoxy group did not influence significantly the yield and the ratio of p/o. Nonpolar solvents such as benzene and hexane were better than polar solvent. Polar solvents such as chloroform and tetrahydrofiiran decreased the yield. It is suggested that these polar solvents may be strongly adsorbed on the surface of the reagent. The reaction did not proceed in ethanol to be due to the elution of copper(II) bromide from the alumina to the solution. It is known that the reaction of aromatic hydrocarbons with copper(II) halides in nonpolar solvents proceeds between aromatic hydrocarbons and solid copper(II) halides and not between hydrocarbons and dissolved copper(II) halides (ref. 6). 

Copper(ii).—Halides. The complex [CuF(aq)] has been identified in copper(ii)-fluoride solutions. The structure of Cs3Cu2Cl.y,2H20 has been reported and the anion is shown in (184). The salts D2[CuX ] (D = the 2,4-dimethyl-... 

This procedure has been used to prepare a variety of substituted a-bromohydrocinnamic acids 2 p-acetyl-a-bromohydro-cinnamic acid was prepared for the first time by this method. The method illustrates a typical application of the Meerwein reaction for the arylation of unsaturated substrates.3 In this reaction a catalytic amount of a copper(I) salt is used to reduce an aryl diazonium salt forming an aryl radical and a copper(II) halide. Addition of the aryl radical to an unsaturated substrate forms an alkyl radical that is reoxidized by the copper(II) halide present forming an alkyl halide and regenerating the copper(I) salt catalyst. In this preparation, the product, an a-bromo acid, is formed in an acidic reaction mixture and dehydro-halogenation does not occur. However, dehydrohalogenation... 

This stereochemistry for the copper(II) ion (Figure 19.1) is unknown in the solid state, but does occur for the copper(II) halides in the vapour state, e.g. CuQ2 (242), as determined by electron diffraction in the gaseous state.417... 

Polymerization also takes place when 4-halo-2.6-disubstituted phenols are oxidized with copper-amine catalysts and oxygen (5,35). In this case, stoichiometric amounts of copper salt or some other chloride acceptor (inorganic bases or strongly basic amines) are necessary since the amine complexes of copper (II) halides are not catalysts for the polymerization. Blanchard (5) has also described the polymerization of these 4-halo-phenols under conditions similar to those used by Price using certain copper (II) complexes as initiators. 

Among the electrochemical syntheses related to the change of metal oxidation number, we emphasize obtaining acetylacetonates of divalent iron, cobalt, and nickel [551,623]. The method of alternating-current electrochemical synthesis was applied to isolate Ji-complexes of monovalent copper with allylamines, allylimines, and ally-lurea from the salts of divalent copper [624-628], We note that the same method was used for preparation of analogous ji-complexes with copper(II) halides (X = Cl, Br) [629a]. Other electrochemical syntheses with participation of metal salts and complexes are described in monographs [201,202] and literature cited therein. 

Aryl halides do not exchange halogens with alkali or earth alkali salts except in the presence of copper (II) oxide in boiling DMF. Copper(II) halides are the preferred reagents for these transformations. Polycyclic bromoquinones are converted to the corresponding chlorides by reaction with copper (I) chloride205. 

Tellurium bis[< -ethyl dithiocarbonate] reacted with the stoichiometrically required amounts of halogens1,2, copper(II) halides, or tellurium tetrachloride1 to produce tellurium (O-ethyl dithiocarbonate) halides. 

The reaction mixtures containing copper(II) halides were stirred for three days and worked up as described above1. 

When the reaction mixtures contain copper(II) halides or copper(II) acetate and hydrogen halide, the diaryl ditellurium compounds are oxidized to the corresponding tellurium dihalides1,2. 

Higher-valent metal halides oxidize diaryl tellurium compounds to diaryl tellurium dihalides. Copper(II) halides can be generated in the reaction mixture from easily accessible copper(II) acetate and hydrohalic acids4. These halogenation reactions are convenient alternatives to the methods using corrosive elemental halogens or sulfuryl halides. 

The yields of the reactions with elemental halogens are almost quantitative, and with the copper(II) halides 82%. 

Reduction of the copper(II) halides to copper(I) halides may be carried out using sulfite or copper metal. If the reduction with copper metal is carried out in concentrated HC1 solution, the solution takes on an intermediate black color before fading to the colorless CuCl ion. The black color is probably due to dimeric or polymeric ions having copper in both the +1 and +2 states, for example, Cl—Cu—Cl—CuC12(H20) . The reduction of divalent copper by cyanide to form the cyano complex, Cu(CN)73, was mentioned in Chapter 10, and the reaction between cupric and iodide ions is similar to this, releasing iodine and forming the very insoluble copper iodide ... 

Facile ligand-transfer oxidation of alkyl radicals is accomplished by copper(II) halides or pseudohalides 143a). Two processes occur simultaneously (1) oxidative substitution via cationic intermediates and an alkylcopper species, as in electron-transfer oxidation processes and (2) homolytic atom transfer. The former is akin to the oxidative displacement... 

One cannot distinguish between the analogous copper intermediates involved in oxidative electron-transfer and ligand-transfer reactions. In each the ionization of the ligand to copper(II) has an important role in the formation of carbonium ion intermediates. A reaction analogous to the copper-catalyzed decomposition of peroxides is the copper-promoted decomposition of diazonium salts (178). The diazonium ion and copper(I) afford aryl radicals which can undergo ligand-transfer oxidation with copper(II) halides (Sandmeyer reaction) or add to olefins (Meerwein reaction). 

Similar cyclopropanation procedures involving copper catalysis are encountered in the reaction of olefins with dibromomalonic esters (217) and Cu in dimethyl sulphoxide and the reaction of olefins with monobromomalonic esters in the presence of DBU and catalytic amounts of copper(II) halide (equation 62) The reaction of ethyl dibromo-acetoacetate (219) with styrene and copper produces the corresponding electrophilic... 

Diaryl tellurium compounds are converted to diaryl tellurium dihalides through reactions with sulfur tetrafluoride triaryl bismuth difluorides , copper(II) halides iron(III) chloride, and mercury(II) chloride ... 

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