Evaluation of the reaction parameters and thermodynamics of the iodide-exchange preparation of radioiodinated 15-(p-iodophenyl) pentadecanoic acid by both solid phase and solution methods

Two isotopic exchange procedures are described for the labelling of 15-(p-iodophenyl) pentadecanoic acid with radioiodine in the presence of ammonium sulphate and cuprous chloride as catalysts The methods afforded regioselective and high specific activity products with radiochemical yields of 92% and 85% within relatively short reaction times. High pressure liquid chromatographic separation resulted in high radiochemically pure product suitable for medical application Kinetic studies revealed second order iodine-iodine exchange reactions with an activation energy of 13 7 Kcal /mole for the solid state radioiodination with ammonium sulphate and 15.3 Kcal/mole for the copper catalyzed exchange reaction.