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 is replaced by a
carbon–hydrogen bond. 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 (C
6F
6) to
pentafluorobenzene
Pentafluorobenzene is an 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 benzene.''CRC H ...
(C
6F
5H) by certain
zirconocene
Zirconocene is a hypothetical compound with 14 valence electrons, which has not been observed or isolated. It is an organometallic compound consisting of two cyclopentadienyl rings bound on a central zirconium atom. A crucial question in researc ...
hydrido complex
Transition metal hydrides are chemical compounds containing a transition metal bonded to hydrogen. Most transition metals form hydride complexes and some are significant in various catalytic and synthetic reactions. The term "hydride" is used ...
es. 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.
Another reaction type is
oxidative addition of a metal into a C-F bond followed by a
reductive elimination step in presence of a hydrogen source. For example, perfluoronated pyridine 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. T ...
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 steps through the
radical anion, the radical and the anion with ultimate loss of a fluorine anion. An example is the conversion of pentafluorobenzoic acid 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 / carborane acid, and NiCl
2(PCy
3)
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
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Organic reactions