Nucleophilic aromatic substitution; kinetics of fluorine-18 substitution reactions in polyfluorobenzenes. Isotopic exchange between 18F− and polyfluorobenzenes in dimethylsulfoxide. A kinetic study

Nucleophilic aromatic substitution reactions of C6F6, C6XF5 (XH, Cl, Br), C6H2F4, oC6H4FNO2 and pC6H4FNO2 by the fluoride anion were studied in DMSO utilizing fluorine-18. Substitution of fluorine by fluorine-18 is the only reaction observed with a C6F6 substrate. With other substrates fluorine substitution is predominant. The kinetic studies provide results consistent with a SNAr two step mechanism and suggest an intermediate analogous to that for electrophilic aromatic substitution. Consideration of σ− indicates consistency with methoxide ion substitution results with similar substrates. The possible utility of these reactions in labeling aromatic compounds is noted.