METAL HALOGENATES

The quaternary ammonium salts (QAS) are widely used as ionofores of ion-selective electrodes and extractants of metals halogenic anion complexes. The influence of the QASes nature with various methyl groups contents on the cadmium extraction from bromide media has been investigated. 

Elements measured Two-thirds of the periodic table transition metals, halogens, lanthanides, and platinum-group metals... 

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]... 

Table 2. Perfluoroalkylmagnesium Halides (RfMgX) Prepared by Metal-Halogen Exchange...

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 ... 

Metal-halogen exchange of 10-bromo-5-ethyl-5//-dibenz[/>,/]azepinc (52) with butyllithium followed by quenching with acetone yields the propan-2-ol 53.214... 

One of the most direct routes to vinylsilanes uses vinyl halides as starting materials. Metal-halogen exchange, followed by electrophilic attack by TMSC1, can often provide the vinylsilane quickly and in good yield. As an added bonus, vinyl bromides have been shown (10, II) to proceed through this sequence with retention of double-bond stereochemistry. 

Metal-halogen stretching vibrations in coordination complexes of gallium, indium and thallium. A. J. Carty, Coord. Chem. Rev., 1969,4, 29-39 (32). 

Metal-metal halogen compounds of the transition metals. J. E. Fergusson, Prep. Inorg. React., 1971, 7, 93-163 (353). 

Helquist and coworkers60 have developed a six-membered ring annulation via a conjugate addition of aryllithium generated by metal-halogen exchange and subsequent intramolecular alkylation. This is illustrated in equation 71. 

McLafferty rearrangement 133, 163 Meisenheimer complexes 699, 702 Metal-chelated intermediates 838 Metal-halogen exchange 781, 784 Methionine, oxidation of 852-855 Methionine sulphone 853 Methionine sulphoxide 851-869 reduction of 1063 residues of... 

As might have been expected, the highest ratio of disubstituted compound, as well as the largest total amount of trifluoromethyl mercurials, was formed by the reagent having the weakest metal-halogen... 

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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