Nucleophilic substitution reaction in polyfluoroaromaticsⅠ.Reactions with secondary amine nucleophiles

Perfluorobenzene,chloropentafluorobenzene and dichlorotetrafluorobenzene werereacted with pyrrolidine,piperidine,morpholine,diethylamine and dipropylamine in aprotic polarsolvents such as DMF and HMPA.With perfluorobenzene monosubstituted products were obtained.Prolonging reaction time or raising the reaction temperature caused the formation of the para disub-stituted products in DMF.With chloropentafluorobenzene,only the para substituted products wereobtained in DMF.Dichlorotetrafluorobenzene was available as an isomeric mixtures of m:o:p=73:18:9.Exceptwith pyrrolidine,only the m-and o-dichlorotetrafluorobenzene reacted with the secondary amines toform the expected products.This is because of the fact that reaction in polar solvents favors theformation of the products with substituent para to chlorine,but the p-dichlorotetrafluorobenzenehas no para fluorine to be attacked.With the most active pyrrolidine however,attack at the positionortho to chlorine occurs.The activity sequence of these secondary amine nucleophiles are attributed to both steric andpolar effect.pyrrolidine>piperidine>morpholine>diethylamine>dipropylamine>diisopropylamineAll of the products were identified by NMR,IR,GLC and elemental analyses and isomeric ratioswere calculated from quantitative NMR measurements.