Free organic halides

Co(TPP) has been demonstrated to act as a catalyst for the electrocarboxylation of benzyl chloride and butyl bromide with CO - to give PhCHiCfOiOCH Ph and Bu0C(0)C(0)0Bu, respectively. The propo.sed mechanism involved Co(TPP)R and [Co(TPP-N-R) as intermediates (the latter detected by spectroscopy) in the catalytic production of free R or R-, which then reacted directly with Co(TPP) precipitated on graphite foil has been successfully used for the determination of organic halides, including DDT and 1,2,3,4,5,6-hexachlorocyclohexane (lindane), to sub-ppm level in aqueous solution. Deoxygenation of the solutions is not required, and the technique is moderately insensitive to the ionic composition of the solution. ... 

Free radicals can also be formed in situ by the abstraction of a halogen atom from an organic halide (RX) as in the sequence of reactions ... 

H. Kotsuki, T. Shimanouchi, R. Ohshima, and S. Fujiwara, Solvent-free organic reactions on silica gel supports. Facile transformation of epoxides to /i-halohy-drins with lithium halides, Tetrahedron, 54 (1998) 2709-2722. 

The dehalogenation of organic halides by organotin hydrides takes place in most cases with a free-radical mechanism [1, 84, 85], The stereospecific reduction of 1,1-dibromo-l-alkenes with Bu3SnH discovered by Uenishi and coworkers [86-89], however, did not occur in the absence of palladium complexes and did not involve radicals. For the synthesis of (Z)-l-bromo-l-alkenes, [(PPh3)4Pd] proved to be the most effective catalyst which could also be generated in situ. The reaction in Eq. (7) proceeded at room temperature and a wide range of solvents could be used. 

The utility of SCFs is not limited to organotransi-tion metal chemistry. scC02 is a promising medium for free-radical carbonylation of organic halides to ketones or aldehydes. As shown in Figure 15A, the... 

If one takes out of this list the polyhalomethanes and tries to understand what the chemistry is about, certainly a simple-minded view is that this is simply a halogen atom abstraction reaction such as one finds in a gas phase reaction, like sodium atom with organic halides. There is a linear free energy correlation in that the logarithms of the rate constants bear a linear relation to one another. 

The reactions of 1,2,5-triphenylphosphole (tpp)(46), 1,2,5-triphenylphosphole oxide (tppO), sulphide (tppS), and selenide (tppSe), with niobium(v) and tan-talum(v) halides in dry, oxygen-free organic solvents have been studied. The complexes formed were characterized by i.r. and X-ray spectroscopy. The... 

J. Dsroszewski, J. Lusztyk, M. Degueil, C. Navarro, and B. Maillard, FleptamelhyItrisiIane-2-thiol-mediated free-radical-chain reduction of organic halides, J. Chem. Soc. Chem. Commun. p. 586 (1991). 

The Organohalogen Component. Just as for Mg and the solvent, the organic halide must be dry (less than 0.02 wt % of H Ol and free of CK The relative reactivity of the halogens is reflected in the rate of disappearance of Mg. which follows ihc general ordei I > Br > Cl > F. Unfortunately, the rate of disappearance Mg of does not always correlate with the formation of active Grignard. Typically, the more reactive the RX is. ihe higher ihc probability of forming a homocoupled product. Therefore. 

Tetraaryl tellurium compounds were prepared from tellurium tetrachloride and lithium halide-free organo lithium compounds3 7. Lithium halide-free organic lithium compounds were synthesized from diaryl mercury and lithium8. 

Free carbon thereby is deposited on the reactive mass of silicon, covering it over and serving as a catalyst for further pyrolysis of methyl groups. Furthermore, the methane and hydrogen which appear in the exit gases impair the efficiency of the condensers and represent a waste of organic halide. For these reasons the formation of trichlorosilanes is to be avoided as uneconomical and detrimental to the continued production of dichlorosilanes. 

The general mechanism in atom transfer radical polymerisation is depicted in Scheme 8.11. The main difference to conventional radical polymerisation is in the presence of a metal complex. Free radicals are generated from reaction between the initiator (such as an organic halide) and the metal species which further controls the reaction by reversibly transforming the free radicals into a dormant species.1"6 However, it ought to be pointed out that in ATRP contrary to, for example, Ziegler-Natta-type catalysts, the polymerisation does not take place at the metal centre. 

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