Why fluoroarenes cannot be prepared by direct reaction of flourine with benzene.

The reaction with fluorine is violent and cannot be controlled. Therefore, fluoroarene cannot be prepared by direct fluorination of aromatic hydrocarbon.

Fluorine is one of the very reactive elements.

The reactions of fluorine are highly exothermic.

Fluorine reacts extremely rapidly with benzene (or other hydrocarbons) and

• It is difficult to control the number of fluorine atoms that are introduced on the benzene ring. A number of fluorinated products are formed hence this reaction is not a good synthesis. Only poor yields of monofluoroaromatic products are obtained by direct fluorination.
• The high energy released in the process is able to break several bonds of the products hence reaction gets uncontrolled product mixture.