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Fluorobenzene

Fluorobenzene
Structure of fluorobenzene
Space-filling model of fluorobenzene
Names
IUPAC name
Fluorobenzene
Other names
Phenyl fluoride
Monofluorobenzene
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.006.657
KEGG
UNII
Properties
C6H5F
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)
low
-58.4·10−6 cm3/mol
Structure
Planar
Hazards
R-phrases (outdated) R36, R37, R38
S-phrases (outdated) S16, S26, S36
NFPA 704 (fire diamond)
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. gasolineHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
3
1
0
Related compounds
Related halobenzenes
Chlorobenzene
Bromobenzene
Iodobenzene
Related compounds
Benzene
1,2-Difluorobenzene
Except where otherwise noted, data are 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. A colorless liquid, it is a precursor to many fluorophenyl compounds.

Preparation

PhF was first reported in 1886 by O. Wallach at the University of Bonn, who prepared the compound in two steps. Phenyldiazonium chloride was first converted to a triazene using piperidine:

[PhN2]Cl + 2 (CH2)5NH → PhN=N-N(CH2)5 + [(CH2)5NH2]Cl

The triazine was then cleaved with hydrofluoric acid:

PhN=N-N(CH2)5 + 2 HF → PhF + N2 + [(CH2)5NH2]F

Historical note: in Wallach’s era, the element fluorine was symbolized with “Fl”. Thus, his procedure is subtitled “Fluorbenzol, C6H5Fl”.[1]

On the laboratory scale, PhF is prepared by the thermal decomposition of the benzenediazonium tetrafluoroborate:

PhN2BF4 → PhF + BF3 + N2

According to the procedure, solid [PhN2]BF4 is heated with a flame to initiate an exothermic reaction, which also affords boron trifluoride and nitrogen gas. Product PhF and BF3 are readily separated because of their differing boiling points.[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 behaves rather differently from other halobenzene derivatives owing to the pi-donor properties of fluoride. For example, the para position is more activated than benzene toward electrophiles. For this reason, it can be converted to 1-bromo-4-fluorobenzene with relatively high efficiency.[3]

Solvent properties

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

PhF is a useful solvent for highly reactive species. Its melting point at -44 °C is lower than that of 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.[4] Fluorobenzene is a relatively inert compound reflecting the strength of the C–F bond.

Although it is usually considered a non-coordinating solvent, a metal complex of PhF has been crystallized.[5]

See also

References

  1. ^ 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
  2. ^ Flood, D. T. (1933). "Fluorobenzene". Org. Synth. 13: 46. doi:10.15227/orgsyn.013.0046..
  3. ^ Rosenthal, Joel; Schuster, David I. (2003). "The Anomalous Reactivity of Fluorobenzene in Electrophilic Aromatic Substitution and Related Phenomena". J. Chem. Educ. 80: 679. doi:10.1021/ed080p679.
  4. ^ Table of Dielectric Constants of Pure Liquids. National Bureau of Standards. 1951.
  5. ^ 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.
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