Iodination Subject

Among nonmetallic materials, glass, chemical stoneware, enameled steel, acid-proof brick, carbon, graphite, and wood are resistant to iodine and its solutions under suitable conditions, but carbon and graphite may be subject to attack. Polytetrafluoroethylene withstands Hquid iodine and its vapor up to 200°C although it discolors. Cloth fabrics made of Saran, a vinyHdene chloride polymer, have lasted for several years when used in the filtration of iodine recovered from oil-weU brines (64). 

Chlorine heptoxide is more stable than either chlorine monoxide or chlorine dioxide however, the CX C) detonates when heated or subjected to shock. It melts at —91.5°C, bods at 80°C, has a molecular weight of 182.914, a heat of vapori2ation of 34.7 kj/mol (8.29 kcal/mol), and, at 0°C, a vapor pressure of 3.2 kPa (23.7 mm Hg) and a density of 1.86 g/mL (14,15). The infrared spectmm is consistent with the stmcture O CIOCIO (16). Cl O decomposes to chlorine and oxygen at low (0.2—10.7 kPa (1.5—80 mm Hg)) pressures and in a temperature range of 100—120°C (17). It is soluble in ben2ene, slowly attacking the solvent with water to form perchloric acid it also reacts with iodine to form iodine pentoxide and explodes on contact with a flame or by percussion. Reaction with olefins yields the impact-sensitive alkyl perchlorates (18). 

The chromatogram is observed and documented as soon as the spots are readily visible. The iodine can then be allowed to evaporate from the chromatogram (fume cupboard ). The chromatogram can then be subjected to further reactions or processes after this reversible reaction. 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

Documentation is carried out as soon as the iodine-colored chromatogram zones can be readily recognized. Then the adsorbed iodine can be allowed to evaporate in the fume cupboard or vacuum desiccator, so that the same chromatograms can be subjected to further reactions and separation steps (e. g. SRS techniques, 2-D separations, coupling techniques such as TLC/GC etc.). The chromatogram zones can also be stabilized by spraying with 0.5 to 1 percent starch solution [4, 5] the well-known blue clathrates that are formed (starch-iodine inclusion compounds) remain stable for months. 

The Ce(IV) oxidation of arsenite has been examined in various acids for which the sequence of rates is HCIO4 >HN03 > H2S04 . The kinetics are simple second order. E in HCIO4 is 9.55 kcal.mole . The chief kinetic interest in this reaction is, however, centred on its remarkable acceleration on addition of minute quantities of iodine , Ru(IV) °- Ru(VI) or Os(Vni) The kinetics are complicated and although catalysis is not the subject of this review, the above references have been included. 

Perhaps the most obvious method of studying kinetic systems is to periodically withdraw samples from the system and to subject them to chemical analysis. When the sample is withdrawn, however, one is immediately faced with a problem. The reaction will proceed just as well in the test sample as it will in the original reaction medium. Since the analysis will require a certain amount of time, regardless of the technique used, it is evident that if one is to obtain a true measurement of the system composition at the time the sample was taken, the reaction must somehow be quenched or inhibited at the moment the sample is taken. The quenching process may involve sudden cooling to stop the reaction, or it may consist of elimination of one of the reactants. In the latter case, the concentration of a reactant may be reduced rapidly by precipitation or by fast quantitative reaction with another material that is added to the sample mixture. This material may then be back-titrated. For example, reactions between iodine and various reducing agents can be quenched by addition of a suitably buffered arsenite solution. 

Mixtures of lithium and bromine are unreactive unless subject to heavy impact, when explosion occurs [1], Lithium and iodine react above 200°C with a large exotherm [2],... 

It was envisioned that hydrindanone 83 and cyclopentene 85 could be used as intermediates in the synthesis of e f-retigeranic acid A (1) and e f-retigeranic acid B (2), respectively. To prepare the building block 90, cyclopentene 85 was reduced with diimide (93 %) in order to prevent isomerization and subsequently deprotected with PPTS to yield hydrindanone 90 (quant.), which could provide access to <77/-retigeranic acid B (2) (Scheme 10.7). Hydrindanone 83 was reduced via an enol triflate and then subjected to Pd-catalyzed reduction to provide cyclopentene 91 (87 % from 83). Upon hydrogenation of 91 with Pd/C and cleavage of the acetal with iodine, protected hydrindanone 92 (95 % from 91) was obtained. The deprotection of 92 provided ent-60, whose enantiomer was used in previous syntheses of retigeranic acid A (1) by Corey [14] and Hudlicky [46, 47]. 

Tapioca and maize amylopectins have been sub-fractionated by fractional precipitation from aqueous solution with increasing amounts of methanol,64 71 and potato amylopectin by preferential precipitation on electrodialysis of the iodine complex.72 When these three amylopectins were subjected to chromatography, and eluted with a neutral buffer, all were found to consist of several sub-fractions.70... 

In reactions with azides, ketones are directly converted to 5-hydroxytriazolines. Ketone enolate 247, generated by treatment of norbornanone 246 with LDA at 0°C, adds readily to azides to provide hydroxytriazolines 248 in 67-93% yield. Interestingly, l-azido-3-iodopropane subjected to the reaction with enolate 247 gives tetracyclic triazoline derivative 251 in 94% yield. The reaction starts from an electrophilic attack of the azide on the ketone a-carbon atom. The following nucleophilic attack on the carbonyl group in intermediate 249 results in triazoline 250. The process is completed by nucleophilic substitution of the iodine atom to form the tetrahydrooxazine ring of product 251 (Scheme 35) <2004JOC1720>. 

The total iodine procedure is claimed to be relatively free from interference by foreign ions. The iodate procedure is subject to interference by bromate and sulfite ions. This method is claimed to be capable of determining down to 0.1 ig iodine in the presence of 500 mg chloride ion and 5 mg of bromide ion. 

The experiments on the iodine separation were conducted as follows. A tubular vessel of pyrex glass, having at one end a plane window and at the other end a conical light-trap, was evacuated and then filled with iodine at about 0.17 mm. pressure, and then with hexene at about 6 mm. partial pressure. The tube was then subjected to the intense light from two Cooper-Hewitt glass mercury arcs, using a filter of 0.05 molal potassium dichromate 2 cm. in thickness to cut off all radiations on the violet side of the green mercury line. The lamps were rim at considerably below the rated capacity, and were cooled by a blast of air to keep the emission lines as narrow as possible. 

K2. Kaplan, E., Edidin, B. D., Fruin, R. C., and Baker, L. A., Intestinal absorption of iodine 131 labelled triolein and oleic acid in normal subjects and in steatorrhea. Gastroenterology 34, 901-909 (1958). 

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