Hydrodefluorination (HDF) is a type of

organic reaction Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, mechanistic organ ...

in which in a substrate of a

carbon–fluorine bond The carbon–fluorine bond is a polar covalent bond between carbon and fluorine that is a component of all organofluorine compounds. It is one of the strongest single bonds in chemistry (after the B–F single bond, Si–F single bond, and H–F ...

is replaced by a

carbon–hydrogen bond In chemistry, the carbon–hydrogen bond ( bond) is a chemical bond between carbon and hydrogen atoms that can be found in many organic compounds. This bond is a covalent bond, covalent, single bond, meaning that carbon shares its outer valence el ...

. The topic is of some interest to scientific research. In one general strategy for the synthesis of fluorinated compounds with a specific substitution pattern, the substrate is a cheaply available perfluorinated hydrocarbon. An example is the conversion of

hexafluorobenzene Hexafluorobenzene, HFB or perfluorobenzene is an organofluorine compound with the chemical formula . In this derivative of benzene, all hydrogen atoms have been replaced by fluorine atoms. The technical uses of the compound are limited, although i ...

(C₆F₆) to

pentafluorobenzene Pentafluorobenzene is a synthetic organofluoride compound with the molecular formula . The compound consists of a benzene ring substituted with five fluorine atoms. The substance is a colorless liquid with a boiling point similar to that of benzen ...

(C₆F₅H) by certain

zirconocene Zirconocene is a Hypothetical chemical compound, hypothetical compound with 18-electron rule, 14 valence electrons, which has not been observed or isolated. It is an Organometallic chemistry, organometallic compound consisting of two Cyclopentadien ...

hydrido complexes. In this type of reaction the thermodynamic driving force is the formation of a metal-fluorine bond that can offset the cleavage of the very stable C-F bond. Other substrates that have been investigated are fluorinated

alkenes 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 ...

. Another reaction type is

oxidative addition Oxidative addition and reductive elimination are two important and related classes of reactions in organometallic chemistry. Oxidative addition is a process that increases both the oxidation state and coordination number of a metal centre. Oxidat ...

of a metal into a C-F bond followed by a

reductive elimination Reductive elimination is an elementary step in organometallic chemistry in which the oxidation state of the metal center decreases while forming a new covalent bond between two ligands. It is the microscopic reverse of oxidative addition, and is ...

step in presence of a hydrogen source. For example, perfluorinated

pyridine Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...

reacts with

bis(cyclooctadiene)nickel(0) Bis(cyclooctadiene)nickel(0) is the organonickel compound with the formula Ni(C8H12)2, also written Ni(cod)2. It is a diamagnetic coordination complex featuring tetrahedral nickel(0) bound to the alkene groups in two 1,5-cyclooctadiene ligands. Thi ...

and

triethylphosphine Triethylphosphine is the organophosphorus compound with the formula P(CH2CH3)3, commonly abbreviated as PEt3. It is a colorless liquid with an unpleasant odor characteristic of alkylphosphines. The compound is a common ligand in organometallic c ...

to the oxidative addition product and then with HCl to the ortho-hydrodefluorinated product. In reductive hydrodefluorination the fluorocarbon is reduced in a series of

single electron transfer In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron. With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spont ...

steps through the

radical anion In organic chemistry, a radical anion is a free radical species that carries a negative charge. Radical anions are encountered in organic chemistry as reduced derivatives of polycyclic aromatic compounds, e.g. sodium naphthenide. An example of a ...

, the radical and the anion with ultimate loss of a fluorine anion. An example is the conversion of

pentafluorobenzoic acid Pentafluorobenzoic acid (PFBA) is an organofluorine compound with the formula C6F5CO2H. It is a white crystalline powder that has a high solubility in water. Its pKa of 1.48 indicates that it is a strong acid.Prakash, G. K. S.; Hu, J. "Pentaflu ...

to 3,4,5-tetrafluorobenzoic acid in a reaction of zinc dust in aqueous ammonia. Specific systems that have been reported for fluoroalkyl group HDF are

triethylsilane Triethylsilane is the organosilicon compound with the formula (C2H5)3SiH. It is a trialkylsilane. The Si-H bond is reactive. It was first discovered by Albert Ladenburg in 1872 among the products of reduction of tetraethyl orthosilicate with sod ...

carborane acid Carborane acids (X, Y, Z = H, Alk, F, Cl, Br, CF3) are a class of superacids, some of which are estimated to be at least one million times stronger than 100% pure sulfuric acid in terms of their Hammett acidity function values (''H''0 ≤ −18 ...

, and NiCl₂(PCy₃)₂ / (LiAl(O-t-Bu)₃H) Juan Xiao, Jingjing Wu, Wenwen Zhao, Song Cao and ''NiCl2(PCy3)2-catalyzed hydrodefluorination of fluoroarenes with LiAl(O-t-Bu)3H'', Journal of Fluorine Chemistry, Volume 146, February 2013, Pages 76-79, ISSN 0022-1139, .

References

{{Reflist Organic reactions