Iodate, formation constants with

Rate = (AriATa + A 2)[Fe ]IC108-] + AsAalFeCl+JfClOa-JfH+l where Kg. is the formation constant of chloric acid and the second term derives from reactive FeCl+ formed during the course of the reaction. In the corresponding reaction with iodate, however, 22 there is no evidence for a rate term involving the reductant. The mechanism involves the reactions... 

Bis(trifluoromethyl) A3-iodane 6a undergoes degenerate ligand exchange with added alkoxide PhC(CF3)2OK more rapidly (second-order rate constant = 49 M 1s 1 at 56 °C) than that of dimethyl A3-iodane 6b (second-order rate constant =61 M 1s 1 at 93 °C), in which an associative mechanism involving the formation of [12-1-4] species was proposed [16]. The CF3 substituents, which lower the electron density on iodine(III) relative to the CH3 substituents, make the iodine of 6a more susceptible to attack by alkoxide ion. Dynamic 19F NMR of A3-iodane 7 showed an intramolecular ligand exchange via intermediacy of bicyclic tetracoordinated iodate with a AG of ca. 12 kcal/mol at - 80 °C [17]. 

The main release of gaseous radionuclides occurs when UNF is breached and dissolved in boiling nitric acid. The following radionuclides iodine-129 (1-129), and krypton-85 (Kr-85) are likely to appear in the off-gas of an air sparge of the dissolver in a conventional PUREX fuel-reprocessing flowsheet. Iodine in the fuel element is believed to occur mainly as iodide (I") however, when contacted with nitric acid, the iodide rapidly oxidizes to elemental I2. Much of the elemental iodine is volatilized to the off-gas, but a portion remains dissolved in solution this ratio (gas phase/liquid phase) is the distribution coefficient or sometimes expressed as a Henry s Law constant. Further oxidation of the liquid phase iodine results in the formation of fhe nonvolatile iodate ion, IO3". However, the formation of the iodate ion occurs slowly and reduction back to elemental iodine is promoted by nitrous acid, which is present in the dissolver system (McKay, Miquel, and White, 1982). 

Upon contact of gas-phase I2 with stainless steel surfaces, a deposited amount of iodine on the order of 0.1 mg /cm was measured, whereas comparable experiments with liquid I2 solution did not result in a measurable deposition of iodine, apparently due to the rapid dissolution of the metal iodides formed (Deane and Marsh, 1990). From the earlier desorption experiments performed by Rosenberg et al. (1969) it was assumed that FeU is the main primary product of this reaction, but that parallel formation of NiU and/or Cris cannot be ruled out all these compounds are readily soluble in water. Experiments using tubes made of steel 1.4541 (Funke et al., 1994) showed an I2 deposition rate constant in dry air at 120 °C of about 6 10" m/s. Under condensing steam conditions at the same temperature a considerably higher value of 1.4- 10 m/s was measured, indicating that under such conditions the U-U conversion on steel surfaces is a fast process. Analysis of the surfaces after completion of the test yielded only a small iodine retention in the condensed steam no iodate could be detected, indicating that no unreacted I2 had passed through the reaction tube and that only metal iodides had been... 

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