Iodine reaction with zinc

Chemical ingenuity in using the properties of the elements and their compounds has allowed analyses to be carried out by processes analogous to the generation of hydrides. Osmium tetroxide is very volatile and can be formed easily by oxidation of osmium compounds. Some metals form volatile acetylacetonates (acac), such as iron, zinc, cobalt, chromium, and manganese (Figure 15.4). Iodides can be oxidized easily to iodine (another volatile element in itself), and carbonates or bicarbonates can be examined as COj after reaction with acid. 

The oxygen atom at 21 is similarly an expendable group. Reaction of 241 (obtained from 185 by the usual procedure for introduction of the 9a-fluoro group) with methanesulfonyl chloride affords the 21 mesylate (242a). Replacement of the leaving group at 21 with iodine by means of potassium iodide in acetone followed by reduction of the halogen with zinc in acetic acid leads to fluorometholone (243). ... 

The filtrate was adjusted to a pH of 9 by adding concentrated ammonia, and than a 1 N aqueous iodine-potassium iodide solution was added dropwise, whereby the tetrahydro-pyrimido-[5,4-d] pyrimidine obtained by hydrogenation with zinc in formic acid was converted by oxidation into 2,6-bis-(diethanolamino)-8-piperidino-pyrimido-[5/4-d]-pyrimidine. The completion of the oxidation was checked by means of a starch solution. The major amount of the oxidation product already separated out as a deep yellow crystalline precipitate during the addition of the iodine solution. After the oxidation reaction was complete, the reaction mixture was allowed to stand for a short period of time, and than the precipitate was separated by vacuum filtration, washed with water and dried. It had a malting point of 157°C to 158°C. The yield was 8.0 g, which corresponds to 95% theory. 

Fleischer1 prepared benzylaniline by heating aniline with benzyl chloride at i6o°. This reaction may be very violent and always leads to mixtures. Bernthsen and Trompetter 2 reduced thiobenzanilide with zinc and hydrochloric acid or sodium amalgam, while O. Fischer 3 reduced bcnzalaniline with sodium and alcohol, to benzylaniline. Knoevenagel4 obtained a 32 per cent yield of benzylaniline from benzyl alcohol and aniline in the presence of iodine. Ullmann5 describes the preparation of benzylaniline from benzyl chloride and excess of aniline at low temperatures. 

The functionalization of zinc porphyrin complexes has been studied with respect to the variation in properties. The structure and photophysics of octafluorotetraphenylporphyrin zinc complexes were studied.762 Octabromoporphyrin zinc complexes have been synthesized and the effects on the 11 NMR and redox potential of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraarylporphyrin were observed.763 The chiral nonplanar porphyrin zinc 3,7,8,12,13,17,18-heptabromo-2-(2-methoxyphenyl)-5,10,15,20-tetraphenylporphyrin was synthesized and characterized.764 X-ray structures for cation radical zinc 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin and the iodinated product that results from reaction with iodine and silver(I) have been reported.765 Molecular mechanics calculations, X-ray structures, and resonance Raman spectroscopy compared the distortion due to zinc and other metal incorporation into meso dialkyl-substituted porphyrins. Zinc disfavors ruffling over doming with the total amount of nonplanar distortion reduced relative to smaller metals.766 Resonance Raman spectroscopy has also been used to study the lowest-energy triplet state of zinc tetraphenylporphyrin.767... 

Lewis acid catalyst is normally required when ammonium polyhalides are used, although recourse does not have to be made to strong acids, such as aluminium trichloride. Bromination and iodination reactions are normally conducted in acetic acid in the presence of zinc chloride [32], but chlorination using the ammonium tetrachloroiodate in acetic acid does not require the additional presence of a Lewis acid [33]. Radical chlorination of toluenes by benzyltrimethylammonium tetrachloroiodate in the presence of AIBN gives mixtures of the mono-and dichloromethylbenzenes [34], Photo-catalysed side-chain chlorination is less successful [35], Radical bromination using the tribromide with AIBN or benzoyl peroxide has also been reported [36, 37],... 

Simdar reactions occur with zinc, magnesium, aluminum, and iron. Concentrated sulfuric acid oxidizes iodide to iodine and bromide to bromine ... 

By contrast, for iodide 18 having the triple bond activated by a phenyl group, conversion to the cyclic organozinc species 25 occurred effectively and the latter could be efficiently functionalized, provided that traces of moisture were excluded by pre-treatment of zinc powder with Mel. The substituted benzylidene cyclopentanes 26 and 27 were respectively obtained after iodinolysis and palladium-catalyzed cross-coupling reaction with benzoyl chloride (equation 10). However, it could not be assessed whether the formation of organozinc 25 was attributable to an anionic or a radical cyclization pathway (or both) as, had iodide 26 been produced by a radical iodine atom-transfer, it would have been converted to 25 by reaction with metallic zinc due to the presence of the activating phenyl group21. 

Thenaldehyde (thiophene-2-carbaldehyde) is readily available via the Vilsmeier-Haack reaction of DMF with thiophene catalyzed by phosphorus oxychloride. The Sommelet reaction with 2-chloromethylthiophene also gives reasonable yields (63AHC(l)l). Likewise, thiophene is readily acylated with acyl anhydrides or acid chlorides (equation 14), using mild Friedel-Crafts catalysts, such as tin(IV) chloride, zinc chloride, boron trifluoride, titanium tetrachloride, mercury(II) chloride, iodine and even silica-alumina gels or low-calcium-content montmorillonite clays (52HC(3)l). 

Fluorine is simultaneously eliminated with other halogens if it is the only halogen vicinal to iodine, bromine or chlorine. The elimination tendency decreases in the series IF > BrF > C1F. The group CF2CHFX is relatively stable towards elimination and requires stronger reaction conditions. The dehalogenation of saturated fluorohalo compounds with zinc dust or zinc/ copper and zinc/silver couples is one of the most useful methods for the preparation of fluoroalkenes (see Table 8). Zinc/zinc(II) chloride has also been used instead of zinc alone. 

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