Iodine purification

The earlier chemical procedures for iodine, which are of interest to radiochemists, have been reviewed by Kleinberg and Cowan (1960). A widely-accepted standard radiochemical procedure for iodine purification was developed by Glendenin and Metcalf (1951). The procedure uses sodium hypochlorite and hydroxylamine hydrochloride in successive steps to ensure radiochemical exchange with the iodine carrier (generally D), followed by carbon tetrachloride-aqueous extractions with nitrite and sulfite for the separation of iodine. The purified iodine is finally precipitated as silver iodide for weighing and counting. Since this procedure has been widely employed, a step-by-step procedure is described below. 

The isotopic composition of fission product iodine present in the BWR reactor water in the case of failed fuel rods in the reactor core is quite similar to that in the PWR primary coolant. Since the iodine purification factor of the reactor water cleanup system is on the order of 100, i. e. virtually identical to that of the PWR primary coolant purification system, this similarity in isotopic composition demonstrates that the release mechanisms of iodine isotopes from the failed fuel rods to the water phase are virtually identical under both PWR and BWR operating conditions. On the other hand, the resulting chemical state of fission product iodine in the BWR reactor water is quite different from that in the PWR primary coolant. The BWR reactor water usually does not contain chemical additives (with the possible exception of a hydrogen addition, see below) as a result of water radioly-... 

The mixture should be colourless, otherwise difficulty will be experienced in the subsequent purification of the product. If the reaction mixture is coloured by iodine (due to volatilisation of some of the mercaptan), add just sufficient ethyl mercaptan to decolourise it. 

The iodide or van Arkel-de Boer process is a volatilization process involving transfer of an involatile metal as its volatile compound. It is used for the purification of titanium. The reaction of iodine gas with impure titanium metal at 175°C yields gaseous titanium iodide and leaves the impurities in the sohd residue. 

The equihbrium is reversed at high temperature. The iodide is decomposed by passing the vapor over an electrically heated wire (1300—1400°C), yielding purified sohd titanium and iodine gas which is recycled. The iodide process also appHes to the purification of zirconium, hafnium, and siUcon. 

An excess of crotonaldehyde or aUphatic, ahcyhc, and aromatic hydrocarbons and their derivatives is used as a solvent to produce compounds of molecular weights of 1000—5000 (25—28). After removal of unreacted components and solvent, the adduct referred to as polyester is decomposed in acidic media or by pyrolysis (29—36). Proper operation of acidic decomposition can give high yields of pure /n j ,/n7 j -2,4-hexadienoic acid, whereas the pyrolysis gives a mixture of isomers that must be converted to the pure trans,trans form. The thermal decomposition is carried out in the presence of alkaU or amine catalysts. A simultaneous codistillation of the sorbic acid as it forms and the component used as the solvent can simplify the process scheme. The catalyst remains in the reaction batch. Suitable solvents and entraining agents include most inert Hquids that bod at 200—300°C, eg, aUphatic hydrocarbons. When the polyester is spHt thermally at 170—180°C and the sorbic acid is distilled direcdy with the solvent, production and purification can be combined in a single step. The solvent can be reused after removal of the sorbic acid (34). The isomeric mixture can be converted to the thermodynamically more stable trans,trans form in the presence of iodine, alkaU, or sulfuric or hydrochloric acid (37,38). 

K2C03 CaH2, CaO or sodium, then fractionally distd. Near-dry alcohol can be further dried by refluxing with magnesium activated with iodine, as described for ethanol. Further purification is possible using fractional crystn, zone refining or preparative gas chromatography. 

Sodium thiocyanate has also been recrystd from water, acetonitrile or from MeOH using Et20 for washing, then dried at 130°, or dried under vacuum at 60° for 2 days. [Strasser et al. J Am Chem Soc 107 789 1985 Szezygiel et al. J Am Chem Soc 91 1252 1987.] (The latter purification removes material reacting with iodine.) Sodium thiocyanate solns can be freed from traces of iron by repeated batch extractions with Et20. 

Iodine monochloride, purchased from J. T. Baker Chemical Company, was used without further purification. 

The commercial recovery of iodine on an industrial scale depends on the particular source of the element.Erom natural brines, such as those at Midland (Michigan) or in Russia or Japan, chlorine oxidation followed by air blowout as for bromine (above) is much used, the final purification being by resublimation. Alternatively the brine, after clarification, can be treated with just sufficient AgNOs to precipitate the Agl which is then treated with clean scrap iron or steel to form metallic Ag and a solution of EeU the Ag is redissolved in HNO3 for recycling and the solution is treated with CI2 to liberate the h ... 

Iodine purchased from Riedel de Haen AG, Seelze-Hannover, Germany, was sublimed before use by the submitters. The checkers used iodine from Siegfried AG, Zofingen, Switzerland. without purification. 

During preparation of hydriodic acid by distillation of phosphorus and wet iodine, the condenser became blocked with by-product phosphonium iodide, and an explosion, possibly also involving phosphine, occurred. There is also a purification hazard. 

For purification of the product, tubes A and B are cleaned, dried, and reassembled with a dry glass-wool insert in B. Tube C, containing the initially formed product, is attached to tube B as shown in Fig. 2. The system is evacuated and this time left open to the vacuum. The two furnaces are separated by ca. 1.5 cm. Furnace I is heated to 80° and furnace II to 130 to 140°. Sublimation is allowed to continue until all the titanium(IV) iodide has left tube C (12 to 16 hours). The purified product crystallizes in tube B at the separation of the two furnaces. The major impurity, iodine, crystallizes in tube A and in the liquid-nitrogen trap. A fluffy tan residue of negligible weight (0.04 to 0.06 g.) remains in tube C. If desired, further purification can be accomplished by moving tube B farther into furnace II, which results in a second sublimation of the product. 

Water purification chemistry, 15 581 Water purification iodine in, 14 373 silver in, 22 655... 

Available from K K Laboratories or may be prepared in 89% yield by the following procedure. To a solution of 393 g. (2.63 moles) of sodium iodide in 1 1. of reagent grade acetone is added 394 g. (2.50 moles) of l-bromo-3 chloropropane (Aldrich Chemical Co.). After stirring 2 hours at room temperature, the mixture is filtered, the sodium bromide is washed with acetone, and the acetone is evaporated at reduced pressure. A dark iodine color is present along with some solid sodium salts. The oil is dissolved in ether, and the solution is washed with a 10% aqueous sodium thiosulfate solution. The ethereal layer is separated, dried over anhydrous sodium sulfate, and evaporated at reduced pressure to yield 454 g. of an oil that can be used without further purification. 

Pyranthrone may be halogenated, for instance, in chlorosulfonic acid in the presence of small amounts of sulfur, iodine, or antimony as a catalyst. This procedure necessitates intermediate separation and purification of pyranthrone after manufacture, because the products, unless purified, fail to furnish the solvent fastness which is characteristic of a typical pigment. 

Volatile substances of which the vapours, on cooling, condense directly to crystals without passing through the liquid phase are sometimes advantageously purified by sublimation, particularly when solubility relations render recrystallisation difficult. The purification of iodine is a well-known case in point. In organic chemistry this process is particularly suitable for quinones. 

A classical example of this process is given by the van Arkel method for the preparation (purification) of several metals. If impure Cr, for instance, is contained together with a small quantity of iodine in a vacuum tube maintained at a temperature at which chromium iodide volatilizes, and a hot zone is created by means of, say, a W filament heated by an electric current, the following reaction will be observed ... 

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