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Fluorobenzene
Identifiers
CAS number 462-06-6 Yes check.svgY
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
NFPA 704.svg
3
1
0
Related compounds
Related halobenzenes Chlorobenzene
Bromobenzene
Iodobenzene
Related compounds Benzene
 Yes check.svgY (what is this?)  (verify)
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 phenyldiazonium 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.

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, pages 255-271.
  3. ^ R.N. Perutz and T. Braun “Transition Metal-mediated C–F Bond Activation” Comprehensive Organometallic Chemistry III, 2007, Volume 1, Pages 725-758. doi:10.1016/B0-08-045047-4/00028-5.
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