Chlorine-iodine exchange

The results of the reaction of benzyl and substituted benzyl halides with metallic nickel powders are summarized in Table 7.13. Benzyl chloride reacted at room temperature with metallic nickel prepared from nickel chloride to give a mixture of the coupled product bibenzyl (40%) and the reduction product toluene (60%). However, the coupled product was found to be formed mainly when the reaction was run at 70°C and when the nickel powders used were prepared from nickel iodide. Under these conditions, a yield of 86% bibenzyl was attained. The fact that iodide ion present in the system facilitates the homocoupling reaction may be ascribed to the chlorine-iodine exchange during the reaction [148]. Higher reaction temperatures such as 70°C may also accelerate the exchange reaction. 

Although organolithium compounds are commonly prepared by a halogen (iodine, bromine or chlorine)-lithium exchange other methodologies involving different starting mate-... 

The rates of reaction of hypophosphorous acid with iodine bromine ", chlorine ", iodine chlorides , iodate , selenious and tel-lurous acids, silver nitrate , cupric chloride and mercuric chloride" (all forming phosphorous acid or phosphites) have been measured, and the results of the earlier work summarized clearly" . All the data are consistent with the hypothesis that there is prior transformation to some reactive form (I). This form (I) does not discriminate very effectively between different oxidants and thus the oxidation steps are presumed to have rates close to the diffusion-controlled limit. The rates of formation of I deduced in these studies are close enough to the rates of deuterium and tritium exchange for the residual difference to represent an isotope effect. Mitchell wrote the formula H5PO3 for I. Others have supposed it to be a tautomer e.g. HPO(OH)2. Both the isotopic exchange results and the oxidation studies require that its formation and decomposition be subject to acid catalysis. For the general mechanism... 

Another important feature of the halogen/metal interconversion is that it proceeds almost exclusively on reactants RX where X is iodine or bromine. In the case of haloarenes, a few examples of chlorine/metal exchange have been reported in very particular cases—strong electron depletion in the arene [31-33] or buttressing effect [34] (vide infra)—but fluorides are unreactive. Iodides are the most reactive toward exchange and are several orders of magnitude faster than bromides. When... 

Iodine Compounds. Hypervalent iodine compounds containing a CF3 group have been prepared by a chlorine-OAc exchange and further reaction with TMSCF3 and TBAT in a one-pot procedure (eq 25). 

Some results are already described in the literature with nickel- or copper catalysts (refs. 3,71-78). It was us possible to develop this exchange and to show that it is under thermodynamic control the equilibrium lies about 60 to 40 % for bromine and iodine, and is much more shifted to the left (95 to 5 %) for chlorine and iodine. 

In the United States and most parts of the world, iodine is obtained com-merciaUy from brine wells. Many subsurface brines have iodine concentrations in the range of 10 to 100 mg/L. Various extraction processes are known including (i) precipitation with silver nitrate, (ii) oxidation with chlorine, and (hi) ion exchange. In the chlorine oxidation process, natural subsurface brine first is acidified with sulfuric acid and then treated with chlorine. Chlorine hberates iodine from the brine solution. Iodine is blown out into a counter-current stream of air. It is dissolved in a solution of hydriodic acid and sulfu-... 

A two-step conversion of acetonide syn-(3R,5S)-6a to hydroxy compound syn-(3R,5S)-12 is known from the patent literature [25]. This compound is an advanced intermediate in the synthesis of HMG-CoA reductase inhibitors [26]. Iodide syn-(3R,5S)-13 has been utilized for this purpose, too.[27] We were able to substitute the chlorine of acetonide sy -(3R,5S)-6a by iodine in a single step under advanced halogen exchange conditions (52% yield Scheme 2.2.7.7) [28]. However, conversion was incomplete (86%) and the remaining starting material could not be removed from the product sy -(3R,5S)-13 [11]. 

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