Fluorobenzene is the
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the formula C
6H
5F, 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
The Rhenish Friedrich Wilhelm University of Bonn (german: Rheinische Friedrich-Wilhelms-Universität Bonn) is a public research university located in Bonn, North Rhine-Westphalia, Germany. It was founded in its present form as the ( en, Rhine ...
, who prepared the compound in two steps.
Phenyldiazonium chloride was first converted to a
triazene
Triazene is an unsaturated inorganic compound having the chemical formula N3 H3. It has one double bond and is the second-simplest member of the azene class of hydronitrogen compounds, after diimide. Triazenes are a class of organic compoun ...
using piperidine:
:
hN2l + 2 (CH
2)
5NH → PhN=N-N(CH
2)
5 +
CH2)5NH2l
The triazine was then cleaved with
hydrofluoric acid:
:PhN=N-N(CH
2)
5 + 2 HF → PhF + N
2 +
CH2)5NH2
Historical note: in Wallach's era, the element fluorine was symbolized with "Fl". Thus, his procedure is subtitled "Fluorbenzol, C
6H
5Fl".
On the laboratory scale, PhF is prepared by the
thermal decomposition
Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is re ...
of the
benzenediazonium tetrafluoroborate:
:PhN
2BF
4 → PhF + BF
3 + N
2
According to the procedure, solid
hN2F
4 is heated with a flame to initiate an
exothermic reaction
In thermochemistry, an exothermic reaction is a "reaction for which the overall standard enthalpy change Δ''H''⚬ is negative." Exothermic reactions usually release heat. The term is often confused with exergonic reaction, which IUPAC defines ...
, which also affords
boron trifluoride and nitrogen gas. Product PhF and BF
3 are readily separated because of their differing
boiling points.
The technical synthesis is by the reaction of
cyclopentadiene with
difluorocarbene
Difluorocarbene is the chemical compound with formula CF2. It has a short half-life, 0.5 and 20 ms, in solution and in the gas phase, respectively.Douglas A Jean Osteraas "Difluorocarbene Modification of Polymer and Fiber Surfaces," ''Journal ...
. 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.
Solvent properties
:
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. 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.
[R.N. Perutz and T. Braun "Transition Metal-mediated C–F Bond Activation" Comprehensive Organometallic Chemistry III, 2007, Volume 1, p. 725–758; .]
See also
*
Bromobenzene
Bromobenzene is an aryl halide, C6H5Br. It is a colourless liquid although older samples can appear yellow. It is a reagent in organic synthesis.
Synthesis and reactions
Bromobenzene is prepared by the action of bromine on benzene in the presenc ...
*
Chlorobenzene
Chlorobenzene is an aromatic organic compound with the chemical formula C6H5Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals.
Uses
Historical
The major use of chlorob ...
*
Iodobenzene
Iodobenzene is an organoiodine compound consisting of a benzene ring substituted with one iodine atom. It is useful as a synthetic intermediate in organic chemistry. It is a volatile colorless liquid, although aged samples appear yellowish.
Pre ...
References
{{fluorine compounds
Fluoroarenes
Phenyl compounds