Copper atoms, reaction + halogens

A key step in the reaction mechanism appears to be nucleophilic attack on the alkyl halide by the negatively charged copper atom but the details of the mechanism are not well understood Indeed there is probably more than one mechanism by which cuprates react with organic halogen compounds Vinyl halides and aryl halides are known to be very unreactive toward nucleophilic attack yet react with lithium dialkylcuprates... 

The most systematic study of reactions of transition metal atoms with halogen compounds has been the work of Klabunde on oxidation of nickel and palladium atoms. Some work has been done with copper, silver, gold, and platinum, but only scattered results have been reported for other metals. Klabunde s research has shown that perfluoroorgano-halides form isolable organometallic compounds on reaction with metal atoms much more commonly than nonfluorinated halides. The types of reactions observed with different classes of organic halides are considered next. 

Chemiluminescence from CaX species (X = halogen) arises from the reaction of copper with Xj molecules. For Cu + Fj, ground-state copper atoms ( 5) react to produce A, B, and C states of CuF, with an inversion of population of the C state relative to the B state observed, whereas metastable Cu atoms ( D) are responsible for chemiluminescent reactions with the other halogens. Emission from GaF and InF ( 11) is seen in reactions of the ground-state Group Ilia atoms with F2, with population inversions formed in the vibrational levels of these excited states the products of ground-state reactions of and... 

A halogen atom directly attached to a benzene ring is usually unreactive, unless it is activated by the nature and position of certain other substituent groups. It has been show n by Ullmann, however, that halogen atoms normally of low reactivity will condense with aromatic amines in the presence of an alkali carbonate (to absorb the hydrogen halide formed) and a trace of copper powder or oxide to act as a catalyst. This reaction, known as the Ullmant Condensation, is frequently used to prepare substituted diphenylamines it is exemplified... 

The reaction mechanism is not rigorously known, but is likely to involve the following steps." " First the arenediazonium ion species 1 is reduced by a reaction with copper-(l) salt 2 to give an aryl radical species 4. In a second step the aryl radical abstracts a halogen atom from the CuXa compound 5, which is thus reduced to the copper-1 salt 2. Since the copper-(l) species is regenerated in the second step, it serves as a catalyst in the overall process. 

Dibromo-l,4-xylene or its 2,5-dichloro derivative is obtained by bromination or, correspondingly, chlorination of 1,4-xylene. It is oxidized to form 2,5-dibro-moterephthalic acid or its dichloro derivative 59. Subsequent reaction with aryl-amine, for instance in the presence of copper acetate, affords 2,5-diarylamino-terephthalic acid 60. It is also possible to replace the halogen atoms stepwise by arylamino moieties [11]. Cyclization to form linear trans-quinacridones, as in the above-mentioned method, is achieved by using acidic condensation agents ... 

Copper iodide acts as an efficient reagent for the nucleophilic displacement of 1-haloalkynes. It transforms 1-bromoalkynes (72) into 1-iodoalkynes (73) which, on further treatment with copper(II) bis(arenesulfinate), are converted into the corresponding alkynyl aryl sulfones (74). An electron transfer between 1-haloalkynes and copper(I) salts is believed to take place for the copper-assisted halogen-exchange reaction at the acetylenic carbon atom. 

The halogens required for this reaction may be generated in situ, for example, through oxidation of hydrogen halides by copper(II) acetate12. Organic vicinal dibromides release their bromine atoms to tellurium13,14. 

In this scheme, Met represents a metal and R-Q-Q-R the initiator (R is a halogen atom or a CN group and Q a diazo or peroxide group). The authors discuss the influence of the instability of C-Met bonds formed with different metals (silver, lead, mercury, iron or copper) [39,45]. Interestingly, in the case of the C-Hg bond, the reaction is as follows ... 

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