Nucleophilic aromatic substitution; kinetics of fluorine-18 substitution reactions in polyfluorobenzenes. Isotopic exchange between fluorine-18(1-) and polyfluorobenzenes in dimethyl sulfoxide. A kinetic study

Nucleophilic arom. substitution reactions of C6F6, C6XF5 (X = H, Cl, Br), C6H2F4, o-C6H4FNO2 and p-C6H4FNO2 by F- were studied in Me2SO utilizing 18F-. Substitution of fluorine by 18F- is the only reaction obsd. with a C6F6 substrate. With other substrates fluorine substitution is predominant. The kinetic studies provide results consistent with an SNAr two-step mechanism and suggest an intermediate analogous to that for electrophilic arom. substitution. Consideration of σ- indicates consistency with MeO- substitution results with similar substrates. The possible utility of these reactions in labeling arom. compds. is noted.