Radioisotopic labelling by surface catalysis—I. Preparation and quality control of 131I-4-iodoantipyrine

No-Carrier-Added Radiohalogenation Methods with Heavy Halogens

“…When comparing isotopie and non-isotopic exchange radioiodination of 4-iodoantipyrine, almost quantitative yields were obtained by iodine replacement, compared to 80% by bromine substitution in acidic aqueous solutions [84,85]. A high yield was also obtained in the iodine-for-bromine substitution in 4-bromometyrapone in a melt of the substrate [86], in bromobenzene in various solvents at 210°C [87,88], and in bromoantipyrine on silica gel [89].…”

“…No mechanism, however, has been proposed for the surface catalysis of radiobromination and iodination by halogen exchange in 4-haloantipyrine [89]. In this case the brominated or iodinated compounds were reacted with the radiohalide on a silica gel surface and the yields for the isotopie and non-isotopic exchange at pH 2 were 95 % and 30%, respectively.…”

“…ICI was used as an oxidizing agent with iodohippuric acid [94] and with iodobenzenes with electron-donating substituents [68,95]. Other in-situ oxidizing agents such as iodate [96][97][98], nitrite [94], hydrogen peroxide [99,100], and chloramine-T [89,101] have also been successfully applied. In ortho-iodohippuric acid, the exchange was equally efficient using nucleophilic and oxidizing conditions [102], whereas in meta-iodobenzylguanidine, oxidation with iodate, nitrite, and ICI did not help [103].…”

“…Generally, a high specific activity is desirable, which can only be achieved by non-isotopic exchange. Although a large fraction of radiohalogenated aromatic compounds have been labeled by halogen exchange reactions, only a few attempts were made to use brominated compounds as precursors for aromatic radioiodination [69,[84][85][86][87][88][89] or radiobromination [90]. When comparing isotopie and non-isotopic exchange radioiodination of 4-iodoantipyrine, almost quantitative yields were obtained by iodine replacement, compared to 80% by bromine substitution in acidic aqueous solutions [84,85].…”

Radioiodination techniques for small organic molecules

“…214 An exchange between radioiodide and hydrogen to form labeled 4-iodoantipyrine has been shown to be catalyzed by silica gel. 215 The mechanism of this reaction is unknown.…”