Fluorobenzene

Fluorobenzene
IUPAC name Fluorobenzene
Other names Phenyl fluoride Monofluorobenzene
Identifiers
CAS number	462-06-6 Y
PubChem	10008
ChemSpider	9614 Y
KEGG	C11272 Y
ChEBI	CHEBI:5115 Y
ChEMBL	CHEMBL16070 Y
Jmol-3D images	Image 1
SMILES Fc1ccccc1
InChI InChI=1S/C6H5F/c7-6-4-2-1-3-5-6/h1-5H Y Key: PYLWMHQQBFSUBP-UHFFFAOYSA-N Y InChI=1/C6H5F/c7-6-4-2-1-3-5-6/h1-5H Key: PYLWMHQQBFSUBP-UHFFFAOYAM
Properties
Molecular formula	C6H5F
Molar mass	96.103
Appearance	Colorless liquid
Density	1.025 g/mL, liquid
Melting point	−40 °C
Boiling point	84–85 °C
Solubility in water	low
Structure
Molecular shape	Planar
Hazards
R-phrases	R36, R37, R38
S-phrases	S16, S26, S36
NFPA 704	3 1 0
Related compounds
Related halobenzenes	Chlorobenzene Bromobenzene Iodobenzene
Related compounds	Benzene 1,2-Difluorobenzene
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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 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.

Preparation

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 cloven 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.

Reactions

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.

References

1. ^ Flood, D. T. (1943), "Fluorobenzene", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV2P0295 ; Coll. Vol. 2: 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.