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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 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 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 (CH2)5NH → PhN=N-N(CH2)5 + CH2)5NH2l The triazine was then cleaved with hydrofluoric acid: :PhN=N-N(CH2)5 + 2 HF → PhF + N2 + CH2)5NH2 Historical note: in Wallach's era, the element fluorine was symbolized with "Fl". Thus, his procedure is subtitled "Fluorbenzol, C6H5Fl". 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: :PhN2BF4 → PhF + BF3 + N2 According to the procedure, solid hN2F4 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 BF3 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

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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 ...
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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 ...
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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