Iodine-131, production distillation methods

Iodine monochloride has been prepared by leading chlorine over solid iodine and distilling the crude product. Despite improvements to obtain a more nearly pure product, this method remains a tedious and time-consuming process. 

Distillation Methods Distillation methods have been widely used in iodine isotope production. Since iodine may be converted to a volatile form (I2), either wet distillation or dry distillation has been employed. A general distillation procedure for carrier-free purification has been reported earlier by Kahn and Freedman (1954). In a wet distillation method (IAEA, 1966), irradiated Te metal is dissolved in a chromic acid-H2S04 mixture. After complete dissolution, the iodate (IO3) formed is reduced to elemental iodine (I2) with oxalic acid and then distilled off from the solution. The distillate is trapped in alkaline sulfite solution. This solution is then purified by an oxidation-reduction cycle and finally redistilled into dilute alkaline solution. In another wet distillation method, irradiated Te02 is dissolved in NaOH and the sodium tellurite is oxidized with H2O2 in the presence of a catalyst, sodium molybdate. The mixture is then acidified with H2SO4 and the iodine is distilled off and trapped in ice-cold water. 

Total SulfuT Dioxide After Alkali Treatment The fact that neutral sodium sulfite does not combine with carbonyl compounds and that the hydroxysulfonic acid compounds are rapidly decomposed on treatment with alkali was used by Ripper (1892) as the basis for the determination of total sulfur dioxide in wine by direct iodine titration. In his method, 50 ml. of wine were pipetted into a 200-ml. flask containing 25 ml. of 1 iV KOH. The mixture was shaken and allowed to stand for 10 to 15 minutes. Then 10 ml. of dilute sulfuric acid (1 + 3) were added, and the solution titrated rapidly with 0.02 N iodine solution to a starch end point which persisted for some time. This method was used as the ofiicial direct titration method for wine in the first edition (1919) of the A.O.A.C. Methods of Analysis in the third (1930) edition it was extended to white grape juice, wine, and similar products (1N NaOH or KOH was used and the solution during standing for 15 minutes was occasionally agitated) hut it was dropped from the fourth (1935) and succeeding editions. Ripper compared his method with the Haas distillation method on ten wines whose SO2 content varied from 42 to 1488 mg. per liter and found the difference between the two to vary from 0 to 5 mg. 

Iodine (I) chloride can be prepared " by the direct interaction of gaseous chlorine with solid iodine so that equimolar amounts of the two elements react together. The product is used without purification, or it is purified by fractional freezing and distillation. The net result of application of these methods of synthesis has been that with no purification the product has been unsatisfactory for many uses, and with too much handling—especially with distillation—the product has also been unsatisfactory. Excessive handling of iodine (I) chloride can give rise to the evolution of chlorine and thus to the reversal of the reaction of synthesis. It can also allow more chance of contact with water so that iodine (V) oxide (a relatively insoluble white solid) forms as a contaminant ... 

For direct introduction of iodine into the nucleus of aromatic hydrocarbons, usually only the most energetic of the methods mentioned on page 152 are useful. Iodination by iodine and HN03 (d 1.5)410 is strongly exothermic and useful for benzene and alkylbenzenes, but phenols and nitrocompounds are formed as by-products the phenols can be removed by shaking the crude product with 10% sodium hydroxide solution, and the nitro compounds by reduction of the crude product with iron filings and hydrochloric acid then the crude solution is made acid to Congo Red and the iodinated aromatic compound is distilled off in steam. 

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