Effects of reaction conditions on rates of incorporation of no‐carrier added F‐18 fluoride into several organic compounds

Apparent rate constants (fractional incorporation per minute per mole of organic reactant) were determined for reaction of no‐carrier added F‐18 fluoride with several aliphatic and aromatic substrates in acetonitrile or DMSO. No large differences were seen between tetraethylammonium and potassium Kryptofix‐2,2,2 as supporting cation. Three hexose derivatives with triflate or cyclic sulfate leaving groups all gave apparent rate constants (obtained by dividing fractional incorporation by time in minutes and by molar concentration of reactant) near 0.4 at 23° and 5 at 55°. An aliphatic iodide reacted ten times more slowly. Aromatic substrates tested showed a wide range of rate constants from >50 at 23° (isotope exchange in 2,4‐dinitrofluorobenzene) to 0.6 at 134° (p‐nitroacetophenone).