Iodination solvent effects

These products are thought to result from attack of an intermediate p-nitro-phenyl radical on the solvent. Evidence for this intermediate was obtained by scavenging the radical with diphenylpicrylhydrazyl, halogens, and nitric oxide.(62) However, the presence of the p-nitrophenetole in the products formed in the presence of iodine, which effectively eliminates most other radical products, suggests that another mechanism involving a phenyl carbonium ion may be also operative ... 

Halogenolysis of zirconacyclopentadienes affords 1,4-dihalodienes (Eq. 2.14) [20]. Solvent effects on halogenolysis are remarkable. Indeed, whereas the iodination of zirconacyclopentadienes in THF with 2 equivalents of I2 affords mainly the monoiodinated diene, the diiododiene can be the major product in CH2C12. For example, 2,3,4,5-tetraethylzirco-nacyclopentadiene reacts with 2 equivalents of I2 in THF at room temperature to give the monoiodinated 3-iodo-4,5-diethylocta-3,5-diene 23 in 70% yield along with only an 18% yield of 3,6-diiodo-4,5-diethylocta-3,5-diene 24 (Eq. 2.14). 

Table 3 The Solvent Effect on lxn Values for the Iodine Oxidation of 5-Trt- and 5-Acm-Protected Peptide Derivatives 451...

The a carbon shifts of haloalkanes depend on temperature and solvent. Strong solvent effects are observed for the iodinated carbon atoms in iodoalkanes, as shown in Table 4.18 [253]. As expected from theory [254], carbon-13 solvent shifts are linearly dependent on (e — l)/(2e + n2) (e dielectric constant n refractive index) [253]. 

When pyridinium hydrochloride was treated at 250°C with iodine monochloride in the presence of aluminium chloride, a 2-pyridylpyridinium salt was formed. Both 1 1 and 1 2 complexes formed when iodine monochloride or iodine reacted with pyridine (80AJC1743). Formation constants for the charge-transfer complexes between iodine and pyridine (and pico-lines) have been measured [84JCS(P2)731], and solvent effects on the... 

Alkenyl(phenyl)iodine(III) compounds can also serve as starting materials in rearrangements. Allenyl(aryl)iodine(III) compounds of type 86 can be synthesized from (diacetoxyiodo) derivatives 85 and propargylsilanes [145]. It depends on the leaving group ability of the aromatic substituent on iodine in 86 as to whether the reaction proceeds via nucleophilic substitution to compounds of type 87 or by an iodonio-Claisen rearrangement to compounds 88, Scheme 37 [146,147]. The easy access to propynyl compounds 87 has been shown [148] and solvent effects in these reactions have been investigated as well [149,150]. 

As was the case for the monofluoro series, halogens attached directly to the CF2 carbon deshield the fluorine nuclei (Tables 4.2 and 4.3). Iodine has the greatest deshielding effect on fluorine chemical shifts I > Br > Cl > F. In contrast, iodine has its usual shielding effect upon carbon chemical shifts. When considering proton chemical shifts for the fluoromethanes, again one must keep in mind the significant solvent effects observed for all di- and trihalomethanes. 

Flavanones undergo a variety of transformations by HTI or other hypervalent iodine reagents. In methanol, at room temperature, they were dehydrogenated to the corresponding flavones [40], A similar dehydrogenation occurred in chromanones [41]. Dramatic solvent effects occurred when methanol was replaced by other solvents. Thus, in trimethyl orthoformate ring-contraction was the main pathway and methyl 2-aryl-2,3-dihydrobenzofuran-3-carboxylates the major products, accompanied by substantial amounts of 3-methoxyflavones [42] ... 

Huebner and Venkataraman69 demonstrated that starch can adsorb iodine from nonaqueous and not necessarily polar solvents, as shown in Table IV. Iodine adsorption by starch in aqueous ethanol increases as the ethanol content increases. Again, the solvent effect depends on the origin of the starch (Table II). The varying effects observed using benzene, ethanol, and chloroform may also be ascribed to the use of starches of different origin... 

As mentioned above, bromine substituents promote the diaryl ether formation, while iodine substitutions prefer to produce diaryls. The ab initio calculations indicate that the O-radicals are stable in bromo derivatives, in contrary to the C-radicals in the iodo derivative, although solvent effects were not taken into consideration. Accordingly, the... 

The electron donor-acceptor molecular complexes between iodine and thiazole, benzothiazole, and some derivatives have been studied in several organic solvents by UV spectroscopy <87CJC468>. In all cases, the presence of the thiazole ring produces a displacement of the Amax iodine band at 512 nm towards shorter wavelengths and a decrease of its absorbance. Moreover, a sharp isosbestic point near 470 nm was observed for all iodine-thiazole complexes. 2-Aryl and 2-hetarylbenzothiazoles showed fluorescence, the maxima of emission being between 350 nm and 395 nm. Both substituent and solvent effects on the spectra were observed <93MI 306-02>. The photophysical properties of bis(benzothiazolylidene)squaraine dyes have also been studied <93JPC13625>. 

In a recent application of DFT to experimentally noted solvent effects on the C shifts in iodoalkynes, it was found that charge transfer complexes from DMSO solvent molecules to the iodine substituent enhanced for the Cl carbon atom [109]. Nevertheless, the overall solvent effects were found to be deshielding, due to changes in ct . Further application of the same method allowed the identification of the first iodo-substituted cumulene in different solvents [110]. 

Lin, C.C. (1968). The Isotopic Exchange of Iodine Atoms between Methyl Iodide and Tetrabutylammonium Iodide. Solvent Effects, Ph.D. Thesis, Department of Chemistry, University of New Mexico. 

Interestingly, the solvent effects and the role of organic compounds on the equihbria in iodine triiodide solutions were studied as early as at the beginning of last century [33]. Though this subject has already a long history it is still considered to be important and draws attention of various research groups [34—40]. 

Polymer Effect of Cold Water Effect of Hot Water After Soaking in Cold Colour Reaction with Iodine Solution Effect of Organic Solvents... 

Cleavage of Pb(C2H5)4 by I2 in polar solvents is slower than that of Pb(CH3>4 [39, 43, 47] and that of Pb(C3H7-n)4 [43]. In nonpolar solvents such as CCI4 and CqHq, a reverse order applies k(Pb(CH3)4)relative reactivities of Pb(C2H5)4 and Pb(CH3)4 are due to transition state solvent effects [43, 52]. Reaction of aqueous iodine solution with Pb(C2H5)4 is reported to be considerably faster than with Pb(CH3)4 [34]. 

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