Fluorobenzene is an

aryl fluoride In organic chemistry, an aryl halide (also known as a haloarene) is an aromatic compound in which one or more hydrogen atoms directly bonded to an aromatic ring are replaced by a halide ion (such as fluorine F''−'', chlorine Cl−1,−3,−5, bro ...

and the simplest of the

fluorobenzenes Fluorobenzenes are a group of aryl fluorides/halobenzenes consisting of one or more fluorine atoms as substituents on a benzene core. They have the formula C6H6–''n''F''n'', where ''n'' = 1–6 is the number of fluorine atoms. Depending on the nu ...

, 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 University of Bonn, officially the Rhenish Friedrich Wilhelm University of Bonn (), is a public research university in Bonn, North Rhine-Westphalia, Germany. It was founded in its present form as the () on 18 October 1818 by Frederick Willi ...

, who prepared the compound in two steps.

Phenyldiazonium Benzenediazonium tetrafluoroborate is an organic compound with the chemical formula, formula 6H5N2F4. It is a salt of a diazonium compound, diazonium cation and tetrafluoroborate. It exists as a colourless solid that is soluble in polar solve ...

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 compound ...

using piperidine: : hN₂l + 2 (CH₂)₅NH → PhN=N-N(CH₂)₅ + CH₂)₅NH₂l The triazine was then cleaved with

hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colorless, acidic and highly corrosive. A common concentration is 49% (48–52%) but there are also stronger solutions (e.g. 70%) and pure HF has a boiling p ...

: :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 of a substance caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic ...

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 ar ...

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 define ...

, which also affords

boron trifluoride Boron trifluoride is the inorganic compound with the formula . This pungent, colourless, and toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds. Structure and bonding The g ...

and nitrogen gas. Product PhF and BF₃ 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 envi ...

s. The technical synthesis is by the reaction of

cyclopentadiene Cyclopentadiene is an organic compound with the chemical formula, formula C5H6. It is often abbreviated CpH because the cyclopentadienyl anion is abbreviated Cp−. This colorless liquid has a strong and unpleasant odor. At room temperature, ...

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 triangular ring. The small size of the ring creates substantial ring strain in the structure. Cyclopropane ...

undergoes a ring expansion and subsequent elimination of

hydrogen fluoride Hydrogen fluoride (fluorane) is an Inorganic chemistry, inorganic compound with chemical formula . It is a very poisonous, colorless gas or liquid that dissolves in water to yield hydrofluoric acid. It is the principal industrial source of fluori ...

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.

References

{{fluorine compounds Fluorobenzenes Phenyl compounds

Preparation

Reactions

Solvent properties

See also

References