Iodide to Iodine

Before the iodide which is concentrated by the thyroid can react with tyrosine, it must be oxidized to iodine. This oxidation must be enzymic, but all attempts to isolate an oxidizing enzyme from the thyroid have so far failed. Dempsey (1944, 1949), however, has demonstrated, by chemocytological methods, both oxidase and peroxidase activity in the gland, the latter being found in follicular cells. De Robertis and Grasso 

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Arsenates(V) are more powerful oxidising agents than phos-phates(V) and will oxidise sulphite to sulphate, hydrogen sulphide (slowly) to sulphur and, depending on the conditions, iodide to iodine. 

Decomposition of most cobalt(III) complexes by boiling with alkali gives a brown precipitate of the hydrated oxide C02O3. aq (p.402). This will quantitatively oxidise iodide to iodine. 

One of the most required methods of determination of iodide-ions in praetiee of ehemieal analysis is photometrie determination of produets of iodination of organie eompounds. The oxidation of iodide to iodine ean be earned out suffieiently seleetively. But in ease of presenee of great abundanee of bromide-ions the seleetive oxidation of iodide-ions is problematie. The variants of determination of iodide-ions with different organie reagents are known, but the absenee of bromide-ions in a system is supposed in most of them. In natural objeets these halides are present simultaneously. 

An important series of reactions, which illustrates the diversity of behaviour to be expected, is the comproportionation of halates and halides. Bromides are oxidized quantitatively to bromine and iodides to iodine, this latter reaction being much used in volumetric analysis ... 

They form a monolayer that is rich in defects, but no second monolayer is observed. The interpretation of these results is not straightforward from a chemical point of view both the electrodeposition of low-valent Ge Iy species and the formation of Au-Ge or even Au Ge h compounds are possible. A similar result is obtained if the electrodeposition is performed from GeGl4. There, 250 20 pm high islands are also observed on the electrode surface. They can be oxidized reversibly and disappear completely from the surface. With Gel4 the oxidation is more complicated, because the electrode potential for the gold step oxidation is too close to that of the island electrodissolution, so that the two processes can hardly be distinguished. The gold step oxidation already occurs at -i-lO mV vs. the former open circuit potential, at h-485 mV the oxidation of iodide to iodine starts. 

A 425-gal tank is filled with water containing 175 g of sodium iodide. How many liters of chlorine gas at 758 mm Hg and 25°C will be required to oxidize all the iodide to iodine ... 

The s-triazines undergo chlorination at nitrogen to yield reactive N-chloro derivatives which oxidize iodide to iodine in the second step. This then forms an intense blue iodine-starch inclusion complex with starch. 

Primary and secondary amines and amides are first chlorinated at nitrogen by the chlorine released by the gradually decomposing calcium hypochlorite. Excess chlorine gas is then selectively reduced in the TLC layer by gaseous formaldehyde. The reactive chloramines produced in the chromatogram zones then oxidize iodide to iodine, which reacts with the starch to yield an intense blue iodine-starch inclusion complex. 

Treatment with chlorine gas converts amines to chloramines, whose active chlorine oxidizes iodide to iodine. This then forms the well-known, deep blue iodine-starch complex [13]. 

A multiwavelength approach might have been considered as an alternative to chemical derivatisation. Ruddle and Wilson [62] reported UV characterisation of PE extracts of three antioxidants (Topanol OC, Ionox 330 and Binox M), all with identical UV spectra and 7max = 277 nm, after reaction with nickel peroxide in alkaline ethanolic solutions, to induce marked differentiation in different solvents and allow positive identification. Nonionic surfactants of the type R0(CH2CH20) H were determined by UV spectrophotometry after derivatisation with tetrabromophenolphthalein ethyl ester potassium salt [34]. Magill and Becker [63] have described a rapid and sensitive spectrophotometric method to quantitate the peroxides present in the surfactants sorbitan monooleate and monostearate. The method, which relies on the peroxide conversion of iodide to iodine, works also for Polysorbate 60 and other surfactants and is more accurate than a titrimetric assay. 

Iodine liberation is one of the oldest and most commonly used methods for assessing lipid substrate oxidation. In this method, hydroperoxides and peroxides oxidize aqueous iodide to iodine, which is then titrated with standard thiosulfate solution and starch as endpoint indicator. The peroxide value is calculated as milliequivalents of peroxide oxygen per kilogram of sample. 

The end-point, which occurs with the complete conversion of iodide to iodine monochloride, is indicated by the disappearance of the violet iodine colour from a chloroform layer present in the titration flask. 

In acetate buffer (pH 4), active chloride stoichiometrically oxidizes iodide to iodine, so that this sensor can be used to determine the concentration of active chlorine. This method is useful for the determination of active chlorine in the range, 3-100 ppb. 

Manganese(lV) oxide is an oxidizing agent. In acid medium, it oxidizes iodide to iodine ... 

Nitrogen dioxide oxidizes an aqueous solution of iodide to iodine, hydrogen sulfide to sulfur, and carbon monoxide to carbon dioxide. In such reaction, it is reduced to nitric oxide, rather than nitrogen ... 

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

By definition POV is the number of miliequivalents of active oxygen per kilogram of sample" , or in some cases the number of micrograms of active oxygen in one gram of sample, capable of oxidizing iodide to iodine" °°. Many of the methods described in Section V for determination of hydroperoxide classes or individual compounds can also be applied for determination of POV, as total hydroperoxides. The iodometric determination of hydroperoxides in lipids and proteins has been reviewed . 

A small amount of iodide is included in the titration mixture. At the end-point the first drop of excess of nitrous acid converts iodide to iodine and this is detected using starch indicator. 

It follows from reactions 15.11 and 15.20 that copper(II) ion can oxidize iodide to iodine, and from reactions 15.11 and 15.21 that thiosulfate can reduce I2 back to I- while forming the tetrathionate ion (Section 3.4). Because the relevant AE° values are several hundred millivolts, the equilibrium constants are large, and these reactions go to essential completion. 

In analogy to sample introduction by hydride generation, mercury trace analysis is possible by reducing Hg compounds to the metal using the cold vapour technique or the determination of iodine at the ultratrace level (after oxidation with 70 % perchloric acid of iodide to iodine) via the gas phase. 

It is not hydrolysed by water but reacts quantitatively with NaOH to yield sodium perchlorate and fluoride. It oxidizes iodides to iodine. Perchloryl fluoride reacts with ammonia to yield ammonium perchlorylamide NH4NHCIO3 [45a]. It reacts with potassium and caesium hydroxide to yield crystalline precipitates of K2NCIO3 and CS2NCIO3. It is isomorphous with metal sulphates, is explosive and very sensitive to flame, shock and friction. 

A small group of cyclic thioureas have been used in the treatment of excessive thyroid function. They include 6-n-propylthiouracil (176 R1 = H, R2 = Prn), 5-iodo-2-thiouracil (176 R1 = I, R2 = H), l-methyl-2-mercaptoimidazole (methimazole) and its ethoxycarbonyl derivative carbimazole (177), which lacks the bitter taste of the unacylated compound. These compounds block the synthesis of thyroxin by inhibiting the oxidation of iodide to iodine and the oxidative coupling of iodotyrosine residues. 

Some 10-X-3 species behave as oxidizing agents. Chloroiodinane (21) oxidizes aqueous potassium iodide to iodine. Brominane (35) oxidizes I, Br- and aniline to I2, Br2 and azobenzene, respectively. 9,10-Dihydroanthracene is dehydrogenated by (35) to give anthracene in quantitative yield (80JA7382). 

Iodic ucid. HIOi. is commonly prepared by oxidizing iodine with HNOr. Il is a strongly oxidizing acid, oxidizing iodide to iodine, xulhtc to sulfate, and H S to sulfur, It reacts vigorously even w ith dry carbon, phosphorus, or organic matin, ... 

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