Formation of Organic Iodides upon Heating Nitric Acid Solutions Containing Carrier-Free lodine-131

When nitric acid solution containing carrier-free 131I was heated, a fraction of the 131I was converted to organic iodides, among which methyl iodide was a major component. The yield of organic iodides showed a strong dependence on the concentration of nitric acid. Furthermore, the yield curve referred to reaction time revealed the particular characteristic of a hump appearing in the case of diluted nitric acid solutions. The distribution of 131I among the various oxidation states in the acid solution has also been studied in its relation to reaction time. The results obtained indicate that organic iodide formation is related with the I°-IO3- oxidation step. The yield curve of the organic iodides is discussed qualitatively, by assuming an intermediate state I* existing between two extreme states of oxidation.