Solution of Iodine in Ethanol

Problem Both iodine and ethanol consist of molecules one can therefore declare both iodine particles and ethanol particles for using the particle model of matter. In order to make the dilution experiment more interesting, one should take iodine crystals in a pipette and demonstrate the larger density of the solution in comparison to the solvent. One can further show the solution of iodine in gasoline and demonstrate the violet color of this solution, however gasoline is a mixture of different hydrocarbons, making the interpretation with particle model more complex. 

Material Gas jar or curette, pipette, forceps iodine, ethanol. 

Procedure Fill a gas jar with ethanol, fix a pipette half-dipped into the ethanol. Take a crystal of iodine and place it in the pipette (see Fig. 4.5). 

Observation A fine stream of brown liquid flows from the pipette and spreads over the bottom of the container. After a while the entire liquid is colored light brown. 

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The crude 2-(2-thiophenyl)pyridine 219 (R2 = H) in ethanol was treated with a saturated solution of iodine in ethanol until the oxidation and precipitation of the crystalline l,2-benzisothiazolo[2,3-a]pyridinium triiodide 222a was complete. This salt 222a was filtered and recrystallized from nitromethane as brown needles (67%) (85CJC882, Scheme 78). 

Prepare a saturated solution of sodium thiosulphate in water and a solution of iodine in ethanol. Add the thiosulphate solution dropwise to the iodine solution cooled in an ice bath, shaking the mixture after each addition until the colour of the iodine fades to a very pale yellow. Allow the tetrathionate formed to crystallise. Collect the crystals by filtration under suction. Wash on the filter with small volumes of ethanol. Dissolve the product in the minimum amount of water and add ethanol to reprecipitate die tetrathionate. This is filtered under suction and washed with small volumes of ethanol and dried by continued suction and then kept in a desiccator with concentrated sulphuric acid as a desiccant. It can be analysed as in Sec.7.3.S. 

A solution of iodine in aqueous iodide has an intense yellow to brown colour. One drop of 0.05M iodine solution imparts a perceptible pale yellow colour to 100 mL of water, so that in otherwise colourless solutions iodine can serve as its own indicator. The test is made much more sensitive by the use of a solution of starch as indicator. Starch reacts with iodine in the presence of iodide to form an intensely blue-coloured complex, which is visible at very low concentrations of iodine. The sensitivity of the colour reaction is such that a blue colour is visible when the iodine concentration is 2 x 10 " 5 M and the iodide concentration is greater than 4x 10 4M at 20 °C. The colour sensitivity decreases with increasing temperature of the solution thus at 50 °C it is about ten times less sensitive than at 25 °C. The sensitivity decreases upon the addition of solvents, such as ethanol no colour is obtained in solutions containing 50 per cent ethanol or more. It cannot be used in a strongly acid medium because hydrolysis of the starch occurs. 

The formation of bromate in hypobromite solutions is about one hundred times as fast as that of chlorate in hypochlorite solutions and occurs readily in slightly alkaline solution, because of the greater hydrolysis of the sodium hypobromite. The velocity of iodate formation in hypoiodite solution proceeds at a much greater rate, about 3,000,000 times that for the chlorate. Hence, hypoiodite solutions are stable only in very low concentration or in the presence of a very small excess of alkali. An increase in temperature increases the rate of iodate formation. Ethanol will react readily with a cold solution of iodine in alkali with the... 

The active bromine can be titrated according to the following procedure about 300 mg. of PTT is dissolved in 50 ml. of acetic acid, 10 ml. of a 5% solution of KI in ethanol is added, and the liberated iodine is titrated with a O.IN solution of NaaSaOg. Percent active bromine calculated 42.5% found 42.1-42.5%. The molecular weight of PTT is 375.96. 

Several papers by Swiatkowski and co-workers, all in Polish, have dealt with various aspects of iodine adsorption by active carbon. Measurements of the adsorption of E from 0.5 M-Nal solutions in aqueous methanol showed that the shift of the inflection point on the isotherm towards lower equivalent iodine concentrations with increase in water concentration in the solvent, was caused partly by the decrease in the solubility of iodine and partly by the effect of water on the polyiodide complex equilibria. For adsorption from solutions of Nal in ethanol, isopropanol, and acetonitrile, the isotherms were of the... 

When an ethanolic solution of the sodium derivative of ethyl malonate is. shaken with a solution of iodine, the latter withdraws the sodium, and the ethyl malonate residues link together in pairs to give the tetra-ethyl ester of... 

The preparation of trimethylantimony diiodide is identical to that of trimethylantimony dichloride up to the point of the addition of chlorine. Instead of a gas inlet tube, an addition funnel is mounted on the flask containing the ice-cold distillate of ethyl ether and trimethylstibine. For a reaction carried out on the basis of 0.25 mol of anhydrous antimony(III) chloride, a solution of 63,5 g. (0.25 mol) of iodine in 400 ml. of ethyl ether is prepared. This solution is added dropwise to the cold distillate. Stirring is maintained and the addition is continued until the color of iodine persists. The precipitate of trimethylantimony diiodide is filtered off on a fritted Buchner fuimel and washed with ethyl ether. The jdeld of the crude product is 47.7 to 65.3 g. (45.0 to 61.8% of theoretical based upon antimony (III) chloride). The diiodide may be recrystallized from ethanol. Anal. Calcd. for (CH3) 3Sbl2 Sb, 28.95 C, 8.55 H, 2.16. Found Sb, 29.31 C, 8.16 H, 2.25. The checkers report that the foregoing syntheses are also satisfactory using one-half the amounts prescribed. 

Sulfhydryl compounds are oxidized with ease to disulfides. It is necessary to employ mild oxidizing agents that do not attack the product. Oxidation of an alkaline solution of n-amyl mercaptan by iodine is described for -amyl disulfide (68%). A mixed disulfide, ethyl /-butyl disulfide, is obtained in 63% yield by treatment of an equimolecular mixture of ethyl and /-butyl mercaptans with iodine in ethanol. Hydrogen peroxide is probably the best reagent for the oxidation. " Halo and amino groups in the molecule are unaffected. Benzoyl disulfide, CtHsCOSSCOCjH, is conveniently prepared by the iodine oxidation of the potassium salt of thiobenzoic acid, C4H5COSK. ... 

The partial iodination of tyrosine in wool by propanolic iodine and its lack of reaction in butanol are explained by the observation that iV-acetyl-tyrosine ethyl ester is more extensively iodinated in ethanol than in propanol (Crewther and Dowling, unpublished observations, 1962). Solutions of I2 in n-butanol do not react with the tyrosine derivative. The results of iodination in different solvents are therefore attributable to differences in chemical equilibria. 

Chlorine is passed into a solution of 38.5 g. (0.25 mole) of acenaph-thene and 0.3 g. of iodine in 100 ml. of glacial acetic acid. (Hood.) The rate of chlorine introduction is 35.5 g. (1.0 gram atom) per hour, and it is passed into the reaction mixture, which is held at 80°, for 30 minutes (0.25 mole). The reaction mixture is fractionally distilled, and the portion boiling in the neighborhood of 163°/13 mm. solidifies into a pale yellow mass melting at 65-66°. The yield is 70%. 5-Chloroacenaphthene melting at 6fi-70° may be obtained by preparation of the picrate derivative, m.p. 137°, and after several recrystallizations from ethanol reconverting to the 5-chloroacenaph-thene by treatment of the picrate with dilute aqueous ammonia. 

A solution of iodine (0.15g, 59 mmol) in 10% aqueous potassium iodide (20 g, 120 mmol in 200 ml) is added dropwise to a stirred solution of imidazole (2.30 g, 34 mmol) in 2m sodium hydroxide (200 ml) at room temperature. The mixture is stirred overnight. Addition of 25% aqueous acetic acid is continued until the mixture is neutral. The white precipitate which forms is filtered, washed with water and air dried before recrystallization from ethanol as colourless crystals (6.42g, 42%), m.p. 197-198°C. 

The characteristic deep blue imparted to a dilute solution of iodine by soluble starch has been used as a sensitive indicator for 150 years. Iodine at a concentration of 10" M is detected readily. The color intensity decreases with increasing temperature, being 10 times less sensitive at 50°C than at 25°C. The sensitivity decreases upon the addition of solvents such as alcohol. No color is observed in solutions containing at least 50% ethanol. 

The solubility of chlorine per 100 cc. of water at 20° is 1.85 g. that of bromine is 3.58 g. and that of iodine 0.28 g. Both chlorine and bromine form crystalline hydrates, C12-8H20 and BrjTOHjO. They are stable only at low temperatures (0-9°). The increased solubility of bromine in potassium bromide solution is ascribed to the formation of KBr if such solutions are saturated with bromine, the vapor pressure of the latter is the same as that of a water solution saturated with bromine. However, the halogen can be removed completely by extraction with carbon disulfide or by a stream of air the KBra must be stable only in the presence of free bromine. The solubility of iodine in water is increased by potassium iodide to 1.4 g. per 100 cc. and in ethanol a 20% solution can be formed. 

The displacement of an adsorbed substance by one that is more readily adsorbed can be shown by placing carbon containing iodine in ethanol or carbon tetrachloride some of the iodine will be eluted. To be effective, this method requires finding a solvent or solute that has much greater affinity for the carbon than does the substance initially adsorbed. Loosely held substances are more completely displaceable. As we move to firmly bonded substances, the utility of the displacement principle greatly diminishes. 

Hydroxy-3,5-diiodophenylacetic acid A solution of iodine (50.8 g) and KI (50.8 g) in water (250 ml) is dropped, with stirring, into a solution of />-hydroxyphenylaceticacid (0.1 mole) in 0.5N-NaOH (800 ml) at room temperature. The mixture is filtered and cooled to 0-5°, then S02 is led in slowly, with stirring, until the pH falls to 2-3. The crude acid that is precipitated is reprecipitated from sodium hydrogen carbonate solution and crystallized from aqueous ethanol. This 4-hydroxy-3,5-diiodophenylacetic acid, obtained in 92% yield, melts at 216.5 to 217.5°. 

Weizmann and Patai865 mixed an ethereal solution of iodine with an alcoholic solution of 4-bromobenzyl cyanide, and an ethanolic sodium ethoxide solution is then dropped in with cooling 4,4/-dibromo-a, a-dicyanostilbene was formed in 78-82% yield. This experiment is derived from work by Chalanay and Knoevenagel.866... 

Charge-transfer (C-T) bands have been located in the spectra of solutions of phenanthridine in 1,2-dimethoxyethane containing bromine solutions containing up to a 2 1 mole ratio of halogen to base were examined, but the structure of the species involved is not clear. Phenanthridine satisfies the conditions necessary for both n and tt- donation and n donation is apparently involved in the charge-transfer interaction with iodine. The equilibrium constant for this reaction has been determined spectrophotometrically, but the claimed correlation (for a series of A -heteroaromatic bases) between values (in 50% ethanol) and these C-T equilibrium constants appears to be an unsatisfactory one and in any case lacks theoretical justification, since it is doubtful whether dissociation constants provide, in general, an accurate measure of w-ionization potentials. In particular, the excellent correlation in the case of phenanthridine is probably fortuitous, since the authors report that w-halogen interactions are markedly sensitive to steric factors which are almost... 

To a solution of 2-acetylfuran 32 (10.0 mL, 100 mmol) in pyridine (25 mL) was added a solution of iodine (25.4 g, 100 mmol) in pyridine (75 mL), and the resulting solution was heated at 100-110 °C for 3 h. The reaction solution was left to stand overnight, filtered, washed with ethanol, and then recrystallized twice in ethanol. The crystal was dried under vacuum to yield compound 33 (17.7 g, 56.3 mmol). Yield 56%. 

Preparation. The principle of the preparation is indicated by equation (8). Of Na 03.5Ht0,250 g. in 150 ml. of H2O is added dropwise to an alcoholic solution of iodine (127 g. of I2 and 50 g. of Nal in 500 ml. of 90% ethanol). The reaction mixture is stirred continuously and maintained below 20° during the addition of the Na2S202. Precipitation of the tetrathionate begins when approximately one-half of the thiosulfate has been added. The reaction is considered complete when the solution becomes straw-colored. At this time 1 liter of absolute ethanol and 500... 

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