Metal—halogen reactions

The electron jump forming Kj BrJ in the K2 + Bf2 collision occurs at a 7A distance. The resulting complex has the biradical structure K K+Br Br [108, 109, 111]. Its principal decay mode is the formation of the di-alkali metal complex K K+Br because, as in alkali metal-halogen reactions, the excess electron of the Bfj moiety induces its dissociation. Most reactive trajectories lead to further dissociation of the complex to K + K+Br, which corresponds to the dominant channel of the reaction, i.e. process 11. The two other reaction channels require a second electron jump, hence forming temporarily K" K Br Br . The hent geometry of the latter complex tends to produce two KBr molecules as in reaction 12, whereas its linear geometry leads to reaction 13. 

The d that measures the reaction cross section may be substantially different from a d determined from gas-phase transport experiments. Ion-molecule and alkali metal-halogen reactions often have cross sections substantially larger than what would be expected from analysis of transport data for the corresponding species. As we have defined Q( ), it is a function of molecular energy however, experimental data usually present Q E), a function of molar energy. At 300 K the mean collision per colliding pair is 6 X10 J (equivalent to 0.04 eV or, in molar units, to 4 kJ mol ). 

This book is unique in that its scope is limited to data about the MTV reaction, application of the reactions related to MTV, and metal-halogen reactions that might be substituted for the MTV reaction. The book provides the reader a single source for research results and data on all compositions related to MTV and the application thereof The breadth of references, figures and tables demonstrate the vast and careful research Dr Koch undertook. 

Many organic halides do not react satisfactorily with lithium to form RLi ecMnpounds or with metallic magnesium to form Grignard reagents. The desired organolithium compound can often be prepared by a halogen-metal interconversion reaction ... 

The halogen-metal exchange reaction was pioneered by Gilman and co-... 

The metal-halogen exchange reaction is useful in the synthesis of numerous perfluoroalkylmagnesium halides, some of which are shown in Table 2... 

Although the metal-halogen exchange reaction is the preferred method of synthesis, the conventional Grignard synthesis through the reaction of a per-fluoroorgano halide and magnesium occasionally is still used [49, 50]... 

Novel polyfluoroethyl Gngnard reagents containmg fluonne, chlorine, and bromine are prepared through the metal-halogen exchange reaction [46] (equation 20)... 

To avoid this competing reaction, the metal-halogen exchange is performed in diethyl ether with either secondary or tertiary butyllithium at -60 °C to give the trifluorovinyllithium compound in near quantitative yield [59],... 

Protection of primary aryl amines as the triazene is accomplished by diazotiza-tion of the amine followed by reaction with pyrrolidine in aq. KOH. This group is stable to metalation of the aromatic ring by metal halogen exchange. The amine is recovered by reductive cleavage with Ni-Al alloy (aq. KOH, rt, 37-68% yield). ... 

Reactivity and yields are greatly enhanced by the presence of 0.5-1% Na in the Li. The reaction is also generally available for the preparation of metal alkyls of the heavier Group 1 metals. Lithium aryls are best prepared by metal-halogen exchange using LiBu" and an aryl iodide, and transmetalation is the most convenient route to vinyl, allyl and other unsaturated derivatives ... 

The chemical reactions of XY can be conveniently classified as (a) halogenation reactions, (b) donor-acceptor interactions and (c) use as solvent systems. Reactions frequently parallel those of the parent halogens but with subtle and revealing differences. CIF is an effective fluorinating agent (p. 820) and will react with many metals and non-metals either at room temperature or above, converting them to fluorides and liberating chlorine, e.g. ... 

An example of intramolecular conjugate addition of aryllithium generated by halogen metal exchange reaction of 92 is illustrated in equation 7966. 

CFaSn bond is stable to reaction conditions that cleave the metal-halogen bond. 

The reactions in this chapter are arranged in order of leaving group hydrogen, metals, halogen, and carbon. Electrophilic substitutions at a nitrogen atom are treated last. 

Limitations common to both salt elimination methods 1 and 2 are (a) the required product may be difficult to separate from the alkali metal halide, (b) reactions are best carried out in the solvent (usually an ether) in which the initial alkali metal derivative is prepared, (c) difficulties may arise through metal-halogen exchange (207), and (d) the range of starting anions is limited [e.g., X3Si compounds are only readily formed when X = H or Ar,... 

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