Exchange of Iodide for Chloride

When treated with potassium iodide, hot, aqueous solutions of triaryl telluronium chlorides precipitate triaryl telluronium iodides (Vol. IX, p. 1080). This halogen exchange reaction was used to isolate triaryl telluronium compounds from the mixtures obtained by reacting tellurium tetrachloride with aryl magnesium bromides (Vol. IX, p. 1080). 

The exchange of chloride for iodide can also be carried out in methanol in which potassium chloride is insoluble  

Triorgano telluronium iodides crystallize easily, whereas the chlorides are often obtained as oils or tars  

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It is the metal catalyzed halogen exchange for haloarenes, that is to say the arylation of halides anions (chloride, bromide, iodide), acting as nucleophiles (Fig. 21). 

Although the initial report included amine nucleophiles, the scope was limited to activated amines such as indole (which actually undergoes C-alkylation at the 3-position), phthalimide, and 7/-methylaniline. Furthermore, enantioselectivities were inferior to those observed with alcohols as nucleophiles. Lautens and Fagnou subsequently discovered a profound halide effect in these reactions. The exchange of the chloride for an iodide on the rhodium catalyst resulted in an increased enantioselectivity that is now comparable to levels achieved with alcoholic nucleophiles ... 

A couple of subsequent reactions which were carried out with the Cp complex 27 all proceeded diastereoselectively, presumably with retention at Ru. These included exchange of the chloride for an iodide ligand under retention as determined by X-ray diffraction, reaction with NaOMe in MeOH to give the neutral monohydride as a single diastereomer, and removal of the chloride with AgBp4... 

In a more recent work Ito [101] has described a simple and highly sensitive ion chromatographic method with ultraviolet detection for determining iodide in seawater. A high-capacity anion exchange resin with polystyrene-divinylbenzene matrix was used for both preconcentration and separation of iodide. Iodide in artificial seawater (salinity, 35 % ) was trapped quantitatively (98.8 0.6%) without peak broadening on a preconcentrator column and was separated with 0.35M sodium perchlorate+ 0.10M phosphate buffer (pH 6.1). On the other hand, the major anions in seawater, chloride and sulphate ions, were partially trapped (5-20%) and did not interfere in the determination of iodide. The detection limit for iodide was 0.2pg L 1 for 6mL of artificial seawater. This method was apphed to determination of iodide (ND-18.3pg L ) and total inorganic iodine (I +I03 -I, 50.0-52.7pg L 1) in seawater samples taken near Japan. 

The redistribution reaction in lead compounds is straightforward and there are no appreciable side reactions. It is normally carried out commercially in the liquid phase at substantially room temperature. However, a catalyst is required to effect the reaction with lead compounds. A number of catalysts have been patented, but the exact procedure as practiced commercially has never been revealed. Among the effective catalysts are activated alumina and other activated metal oxides, triethyllead chloride, triethyllead iodide, phosphorus trichloride, arsenic trichloride, bismuth trichloride, iron(III)chloride, zirconium(IV)-chloride, tin(IV)chloride, zinc chloride, zinc fluoride, mercury(II)chloride, boron trifluoride, aluminum chloride, aluminum bromide, dimethyl-aluminum chloride, and platinum(IV)chloride 43,70-72,79,80,97,117, 131,31s) A separate catalyst compound is not required for the exchange between R.jPb and R3PbX compounds however, this type of uncatalyzed exchange is rather slow. Again, the products are practically a random mixture. 

Other procedures for the simultaneous determination of chlorides, bromides and iodides were suggested by Russel [576], He analysed 2-haloethanols produced by the reaction of ethylene oxide with HC1, HBr and HI. A sample of halides was converted into halic acids with the aid of a strongly acidic ion exchanger. Ethylene oxide was allowed to pass through 10 ml of the acids cooled to 4°C for 15 min. In another procedure, 1 ml of liquid ethylene oxide was added to the acids. After 1 h, the sample was diluted to 15 ml and 1 fi was analysed using 12% of EGS at 100°C. The method was illustrated on the... 

DBU has been quaternized with chloromethylated polystyrenes to give new ion-exchange resins (84BCJ1108). The chloride forms of these ion-exchange resins were effective as ion exchangers for bulky anions such as sulfate, oxalate, hexacyanoferrate(II) and (III), and tris(oxalato)ferrate(III). The adsorption of mercury(II) and copper(II) chlorides and iodides on these resins was also investigated. 

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