Preparation of no carrier added fluorine-18 labeled 16-fluorohexadecanoic and fluoroacetic acids from highly reactive tetraethylammonium [¹⁸F]fluoride

No carrier added tetraethylammonium [¹⁸F]fluoride prepared via synthesis and hydrolysis of fluorotrimethylsilane was reacted with methyl 16-iodohexadecanoate in acetonitrile. At 80°C, yields of up to 80% were found with reaction times of 20-30 min. As would be expected for fluoride-for-iodide exchange, reactions were slower than previously-reported cyclic sulfate and triflate displacements. TLC and reverse-phase HPLC indicated that a single pure radioactive product was formed, which was hydrolyzed with alkali to the free acid. NMR spectroscopy of a carrier added preparation was consistent with assignment as 16-fluorohexadecanoic acid and no rearrangement to the 15-fluoro compound. [¹⁸F]Fluoroacetic acid was prepared analogously in high yield from ethyl iodoacetate. The results are discussed in terms of guidelines for syntheses of other ¹⁸F compounds and of the properties of near anhydrous tetraethylammonium fluoride in acetonitrile.