Liberation of free iodine

Ethyl iodide is a heavy liquid, of b.p. 72° and of d, 1 94 insoluble in water, When freshly distilled it is colourless, but on prolonged exposure to light it darkens in colour owing to the liberation of free iodine. Its chemical properties are almost identical with those of ethyl bromide given on pp. 102 and 103. 

It was used earlier as an antiseptic but the antiseptic properties are due to the liberation of free iodine and not due to iodoform itself. Due to its objectionable smell, it has been replaced by other formulations containing iodine. 

In the following method a slight excess of an alcoholic solution of bromine is added to an alcoholic solution of the tautomeric mixture the excess of bromine is immediately removed by the addition of a few drops of alcoholic /3-naphthoI solution potassium iodide solution is next added, and the hydrogen iodide formed by interaction with the hydrogen bromide present reduces the bromo-ketone with liberation of free iodine, which is estimated by titration with standard thiosulphate (in absence of starch). One molecule of iodine = one molecule of enolic compound. For criticism of this method, see Ann. Rep., 1930, 100. 

Iodine forms compounds with all elements except the noble gases, sulfur, and selenium, but only reacts indirectly with carbon, nitrogen, oxygen, and some noble metals. Ferric and cupric salts, and compounds of vanadium, chromium, and manganese in their highest oxidation status are reduced in acid solution by iodide ions, with liberation of free iodine. Iodine reacts with hydrocarbons, but equilibria are often unfavorable because hydrogen iodine is liberated, which may reduce the alkyl iodide to the hydrocarbon with formation of iodine. 

Organic peroxides Hydriodic acid. Spray plate with a reagent comprising 40 ml glacial acetic acid and 0.2 g zinc dust added to 10 ml of 4% aqueous potassium iodide, then spray with fresh 1% starch solution. Peroxides (and certain other types of oxidising agents) revealed by liberation of free iodine. Alternatively use 2,6-dibromobenzoquinone chlorimine. [28]... 

The Karl Fischer procedure has now been simplified and the accuracy improved by modification to a coulometric method (Chapter 14). In this procedure the sample under test is added to a pyridine-methanol solution containing sulphur dioxide and a soluble iodide. Upon electrolysis, iodine is liberated at the anode and reactions (a) and (b) then follow the end point is detected by a pair of electrodes which function as a biamperometric detection system and indicate the presence of free iodine. Since one mole of iodine reacts with one mole of water it follows that 1 mg of water is equivalent to 10.71 coulombs. 

Colorless or white cubic crystals or granules becomes yellowish when exposed to bright light due to photochemical decomposition liberating traces of free iodine density 3.13 g/cm melts at 681°C vaporizes at 1,330°C highly soluble in water, 140 g/lOOmL at 20°C aqueous solution readily dissolves iodine sparingly soluble in ethanol (about 2 g/lOOmL at 25°C) and acetone slightly soluble in ether and ammonia. 

The total amount of iodine present in the sample in all forms was thus determined. If bromide—bromate reagent with 2 N acetic acid and 0.05 N sulphuric acid was applied to the liberation of bound iodine, the result did not include tightly bound iodine, which can be released only by wet or dry ashing. With the omission of this step from the procedure, a result was obtained which represented iodide and free iodine only without the addition of iodate, free iodine only was determined. 

Kesari et al. (Kesari et al., 1998) developed a simple and sensitive spectrophotometric method for the determination of iodine in tap water, sea water, soil, iodized salt and pharmaceuticals samples. The said method was based on oxidation of F to lOs" with bromine water and liberation of free I2 from IQ3" by addition of K1 in acidic medium. I2 is then reacted with leuco crystal violet and the crystal violet dye liberated shows maximum absorbance at 591 nm. Beer s law is obeyed over the concentration range from 0.04 to 0.36 mg/1 of iodine in a final solution volume of 25 ml. The method is free of interference of other major toxicants. 

MIT, DIT, and Tx in the thyroid extracts of rats injected 48 hours previously with I were first identified as free amino acids along with three unknown substances (16,31). One of the unknowns was later shown to be TRITh (63,67) and traces of MIH were regularly found by the writers. Autography is the best technique for studying the free amino acid of thyroid because the amino acids contain only a very small part of total radioactivity (a few per cent). Since the proteolysis of thyroglobulin seems to be complete and does not cause liberation of iodothyronines faster than iodotyrosines, the composition of the mixture of free iodinated amino acids is similar to that of samples obtained by in vitro hydrolysis of the protein... 

Transfer 25 ml. of this dilute solution by means of a pipette to a conical flask, and add similarly 50 ml. of Ml 10 iodine solution. Now-add 10% sodium hydroxide solution until the liquid becomes pale yeilow in colour, and allow the solution to stand, with occasional shaking, at room temperature for at least 10 minutes. Then acidify with dilute hydrochloric acid (free from chlorine) in order to liberate the remaining iodine. Titrate the latter w ith Mho sodium thiosulphate solution, using starch as an indicator in the usual way. 

The most characteristic property of the oxaziranes is tlieir strong oxidizing character which is approximately equal to that of hydrogen peroxide. Oxaziranes react with hydrochloric acid the chlorine thus liberated is, however, used up in secondary reactions. " Two equivalents of iodine are formed from acid iodide solutions according to Eq. Titration of the free iodine allows a simple estimation of... 

A variation of the general method for the synthesis of 2-amino-selenazoles is to avoid the use of the free a-halogenocarbonyl compound and in its place react the corresponding ketone and iodine with selenourea.This procedure is also taken from thiazole chemistry. By contrast with thiourea, the reaction with selenourea needs a longer reaction time and the work up of the reaction mixture is somewhat more difficult. Usually an excess of the ketone is used. In the preparation of 2-amino-4-( n-nitrophenyl)selenazole, a very high yield, calculated on the amount of iodine used, was obtained. To explain this peculiar result, the oxidative action of the nitro group was invoked. This liberates free iodine from some of the hydrogen iodide eliminated in the condensation reaction, and the free iodine then re-enters into the reaction. 

On the basis of experiments with myoinositol (50), it has been suggested that triose reductone should be oxidized by periodate to yield two molar equivalents of formic acid and one molar equivalent of carbon dioxide. However, it has been reported by two groups (1,29) that crystalline triose reductone is oxidized by two moles of periodic acid to give formic acid and glyoxylic acid, free iodine being liberated during the... 

Hesse and Mix (29) oxidized a relatively concentrated solution of triose reductone using limited amounts of free periodic acid. In these conditions, the iodic acid formed by the initial reduction of periodic acid could be further reduced and the reduction product could then, in turn, react with the remaining periodic acid and liberate iodine. Thus glyoxylic acid could be isolated from the oxidation mixture, as no periodate was available for its oxidation. 

Iodine has anti-infective action against many bacteria, fungi, viruses, yeasts, and protozoa. Fbvidone-iodine (Betadine) is a combination of iodine and povidone, which liberates free iodine. Fbvidone-iodine is often preferred over iodine solution or tincture because it is less irritating to the skin. Unlike with the use of iodine, treated areas may be bandaged or taped. 

W.M. Fischer A. Schmidt, Ber 57, 693—98 (1924) 59, 679-82(1926) (Determination of ethanol or methanol by means of Na nitrite, followed by removal of ethyl-, or methyl-nitrite, witb a current of carbon dioxide, followed by absorption of gas in coned Na bicarbonate soln. On action of KI soln in dilute HCl on the soln contg nitrites, the iodine is liberated and then the free iodine... 

F. C. Mathers and C. G. Schluderberg 124 prepared indium iodate, In(I03)3, by mixing soln. of indium trichloride and potassium iodate. The precipitate is amorphous. The mixture was evaporated to dryness on a water-bath the residue extracted on a Gooch s crucible with warm water and dried in vacuo over sulphuric acid. The mass was dissolved in boiling nitric acid (1 10), and on evaporation white crystals of indium iodate were formed. 100 grms. of water at 20° dissolve 0 067 grm., and 100 grms. of nitric acid (1 5) at 80° dissolve 0 67 grm. of the salt. It also dissolves in dil. sulphuric or hydrochloric acid. The soln. in the last-named add decomposes with the liberation of chlorine. The crystals decompose with the evolution of iodine when heated by a free flame and explode if touched with a red-hot iron wire. 

The detection and determination ot the perchlorates.—The perchlorates give no precipitates with silver nitrate or barium chloride soln. cone. soln. give a white crystalline precipitate with potassium chloride. Unlike all the other oxy-acids of chlorine, a soln. of indigo is not decolorized by perchloric acid, even after the addition of hydrochloric acid and they do not give the explosive chlorine dioxide when warmed with sulphuric acid unlike the chlorates, the perchlorates are not reduced by the copper-zinc couple, or sulphur dioxide. Perchloric acid can be titrated with —iV-alkali, using phenolphthalein as indicator. The perchlorates can be converted into chlorides by heat and the chlorides determined volumetrically or gravimetrically they can be reduced to chloride by titanous sulphate 28 and titration of the excess of titanous sulphate with standard permanganate they can be fused with zinc chloride and the amount of chlorine liberated can be measured in terms of the iodine set free from a soln. of potassium iodide and they can be... 

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