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 U ...
, who prepared the compound in two steps.
Phenyldiazonium
Benzenediazonium tetrafluoroborate is an organic compound with the formula 6H5N2F4. It is a salt of a diazonium cation and tetrafluoroborate. It exists as a colourless solid that is soluble in polar solvents. It is the parent member of the ary ...
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
Hydrofluoric acid is a Solution (chemistry), solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly Corrosive substance, corrosive. It is used to make most fluorine-containing compounds; examples include th ...
:
: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
Benzenediazonium tetrafluoroborate is an organic compound with the formula 6H5N2F4. It is a salt of a diazonium cation and tetrafluoroborate. It exists as a colourless solid that is soluble in polar solvents. It is the parent member of the ary ...
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 point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding envir ...
s.
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
Cyclopropane is the cycloalkane with the molecular formula (CH2)3, consisting of three methylene groups (CH2) linked to each other to form a ring. The small size of the ring creates substantial ring strain in the structure. Cyclopropane itself ...
undergoes a ring expansion and subsequent elimination of
hydrogen fluoride
Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock i ...
.
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 presen ...
*
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