Radioisotopic labelling by surface catalysis

The mechanism of iodine for hydrogen and iodine for halogen exchange on chromatographic surfaces has been investigated by allowing no-carrier-added 131I- to react with model aromatic compounds. Reactions with phenol and aniline resulted in 2- and 4-position substitution. The absolute yield and 2:4 ratio varied as a function of initial solvent used; hydrogen ion concentration; type of chromatographic surface; and contact time on the surface. Reaction with iodo- and bromophenols revealed that iodine for hydrogen exchange occurs more readily than iodine for halogen exchange. The results indicate that with aromatic systems the reactions occur by electrophilic substitution, the iodinating species arising from surface catalysed oxidation of 131I-. (author)