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Structure of fluorobenzene
Space-filling model of fluorobenzene
IUPAC name
Other names
Phenyl fluoride
CAS number 462-06-6 YesY
ChemSpider 9614 YesY
Jmol-3D images Image
KEGG C11272 YesY
PubChem 10008
Molar mass 96.103
Appearance Colorless liquid
Density 1.025 g/mL, liquid
Melting point −44 °C (−47 °F; 229 K)
Boiling point 84 to 85 °C (183 to 185 °F; 357 to 358 K)
Molecular shape Planar
R-phrases R36, R37, R38
S-phrases S16, S26, S36
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Related compounds
Related halobenzenes
Related compounds
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

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, indicative of the remarkable effect of fluorination on the intermolecular interactions as seen throughout organofluorine chemistry. In contrast, the boiling points of PhF and benzene differ by only 4 °C.


On the laboratory scale, PhF is conveniently prepared by the thermal decomposition of the benzenediazonium tetrafluoroborate[1]

PhN2BF4 → PhF + BF3 + N2

According to the procedure, solid [PhN2]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 piperidinide, which in turn was cleaved using hydrofluoric acid.

[PhN2]Cl + 2 C5H10NH → PhN=N-NC5H10 + [C5H10NH2]Cl
PhN=N-NC5H10 + 2 HF → PhF + N2 + [C5H10NH2]F

An interesting historical note: in Wallach’s era, the element fluorine was symbolized with “Fl”. Thus, his procedure is subtitled “Fluorbenzol, C6H5Fl”.[2]

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.[3]

Structure of [(C5Me5)2Ti(FC6H5)]+, a coordination complex of fluorobenzene.

Fluorination of fluorobenzene gives mainly 1,2-difluorobenzene.


  1. ^ Flood, D. T. (1943). "Fluorobenzene". Org. Synth. ; Coll. Vol. 2, p. 295 .
  2. ^ Wallach, O. “Über einen Weg zur leichten Gewinnung organischer Fluorverbindungen” (Concerning a method for easily preparing organic fluorine compounds) Justus Liebig's Annalen der Chemie, 1886, Volume 235, p. 255–271; doi:10.1002/jlac.18862350303
  3. ^ R.N. Perutz and T. Braun “Transition Metal-mediated C–F Bond Activation” Comprehensive Organometallic Chemistry III, 2007, Volume 1, p. 725–758; doi:10.1016/B0-08-045047-4/00028-5.