Electrofluorination
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Electrochemical fluorination (ECF), or electrofluorination, is a foundational organofluorine chemistry method for the preparation of
fluorocarbon Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often have distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Several fluorocarbons and their derivatives are ...
-based organofluorine compounds.G. Siegemund, W. Schwertfeger, A. Feiring, B. Smart, F. Behr, H. Vogel, B. McKusick "Fluorine Compounds, Organic" in "Ullmann’s Encyclopedia of Industrial Chemistry" 2005, Wiley-VCH, Weinheim. The general approach represents an application of electrosynthesis. The fluorinated
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 ...
s produced by ECF are useful because of their distinctive
solvation Solvations describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the solute, includi ...
properties and the relative inertness of carbon–fluorine bonds. Two ECF synthesis routes are commercialized and commonly applied: the Simons process and the Phillips Petroleum process. It is also possible to electrofluorinate in various organic media.Fred G. Drakesmith "Electrofluorination of Organic Compounds" Topics in Current Chemistry, Vol. 193, Springer, Berlin-Heidelberg, 1997. Prior to the development of these methods, fluorination with
fluorine Fluorine is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...
, a dangerous
oxidizing agent An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...
, was a dangerous and wasteful process. ECF can be cost-effective, but it may also result in low yields.


Simons process

The Simons process, named after Joseph H. Simons entails
electrolysis In chemistry and manufacturing, electrolysis is a technique that uses Direct current, direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of c ...
of a solution of an
organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
in a solution 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 ...
. An individual reaction can be described as: :R3C–H + HF → R3C–F + H2 In the course of a typical synthesis, this reaction occurs once for each C–H bond in the precursor. The cell potential is maintained near 5–6 V. The
anode An anode usually is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, which is usually an electrode of the device through which conventional current leaves the devic ...
is
nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
-plated. Simons discovered the process in the 1930s at Pennsylvania State College (U.S.), under the sponsorship of the 3M Corporation. The results were not published until after World War II because the work was classified due to its relevance to the manufacture of uranium hexafluoride. In 1949 Simons and his coworkers published a long paper in the ''Journal of the Electrochemical Society''. The Simons process is used for the production of perfluorinated
amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...
s,
ether In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R ...
s,
carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...
s, and
sulfonic acid In organic chemistry, sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula , where R is an organic alkyl or aryl group and the group a sulfonyl hydroxide. As a substituent, it is kn ...
s. For carboxylic and sulfonic acids, the products are the corresponding acyl fluorides and sulfonyl fluorides. The method has been adapted to laboratory-scale preparations. Two noteworthy considerations are (i) the hazards associated with hydrogen fluoride (the
solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
and fluorine source) and (ii) the requirement for
anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...
conditions.


Phillips Petroleum process

This method is similar to the Simons Process but is typically applied to the preparation from volatile hydrocarbons and chlorohydrocarbons. In this process, electrofluorination is conducted at porous
graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...
anodes in molten potassium fluoride in hydrogen fluoride. The species KHF2 is relatively low melting, a good electrolyte, and an effective source of fluorine. The technology is sometimes called “CAVE” for Carbon Anode Vapor Phase Electrochemical Fluorination and was widely used at manufacturing sites of the 3M Corporation. The organic compound is fed through a porous anode leading to exchange of fluorine for hydrogen but not chlorine.


Other methods

ECF has also been conducted in organic media, using for example organic salts of fluoride and
acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not class ...
as the solvent. A typical fluoride source is (C2H5)3N:3HF. In some cases, acetonitrile is omitted, and the solvent and electrolyte are the triethylamine-HF mixture. Representative products of this method are fluorobenzene (from benzene) and 1,2-difluoro
alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in whi ...
s (from
alkene In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins. The Internationa ...
s).


References

{{Reflist Organofluorides Chemical synthesis Chemical processes Electrolysis Hydrogen production ConocoPhillips