Fluorobenzene

Fluorobenzene is the chemical compound with the formula C6H5F, often abbreviated PhF. This species is a derivative of benzene, with a single fluorine atom attached. Fluorobenzene is the chemical compound with the formula C6H5F, often abbreviated PhF. This species is a derivative of benzene, with a single fluorine atom attached. Its melting point is -44 °C, which is lower than that of benzene, as a result of the reduced symmetry of the molecule compared to benzene. In contrast, the boiling points of PhF and benzene are very similar, differing by only 4 °C. It is considerably more polar than benzene, with a dielectric constant of 5.42 compared to 2.28 for benzene at 298 K. On the laboratory scale, PhF is conveniently prepared by the thermal decomposition of the benzenediazonium tetrafluoroborate According to the procedure, solid BF4 is heated with a flame to initiate an exothermic reaction that affords two volatile products, PhF and BF3, which are readily separated because of their differing boiling points. PhF was first reported in 1886 by O. Wallach at the University of Bonn, who prepared the compound in two steps, starting also with a phenyldiazonium salt. The diazonium chloride was first converted to its piperidine triazene, which in turn was cleaved using hydrofluoric acid. Historical note: in Wallach’s era, the element fluorine was symbolized with “Fl”. Thus, his procedure is subtitled “Fluorbenzol, C6H5Fl”. The technical synthesis is by the reaction of cyclopentadiene with difluorocarbene. The initially formed cyclopropane undergoes a ring expansion and subsequent elimination of hydrogen fluoride. PhF is a relatively inert compound because the C–F bond is very strong. PhF is a useful solvent for highly reactive species, but a metal complex has been crystallized.