Halogenation
In
drugs.[1] This kind of conversion is in fact so common that a comprehensive overview is challenging. This article mainly deals with halogenation using elemental halogens (F2, Cl2, Br2, I2). Halides are also commonly introduced using salts of the halides and halogen acids.[clarification needed] Many specialized reagents exist for and introducing halogens into diverse substrates, e.g. thionyl chloride
.
Organic chemistry
Several pathways exist for the halogenation of organic compounds, including
organofluorine
compounds are highly stable.
Free radical halogenation
Halogenation of
alkanes is largely determined by the relative weakness of the C–H bonds. This trend is reflected by the faster reaction at tertiary and secondary
positions.
Fluorinations with elemental
organic compounds are fluorinated using this technology. Aside from F2 and its electrochemically generated equivalent, cobalt(III) fluoride
is used as sources of fluorine radicals.
Free radical chlorination is used for the industrial production of some
solvents:[2]
- CH4 + Cl2 → CH3Cl + HCl
Naturally-occurring
]The
methyl ketones
, proceeds by the free radical iodination.
Addition of halogens to alkenes and alkynes
alkynes
, add halogens:
- R−CH=CH−R' + X2 → R−CHX−CHX−R'
In
1,2-dichloroethane
:
- 4 HCl + 2 CH2=CH2 + O2 → 2 Cl−CH2−CH2−Cl + 2 H2O
The addition of halogens to alkenes proceeds via intermediate halonium ions. In special cases, such intermediates have been isolated.[4]
Bromination is more
exothermic. Illustrative of the bromination of an alkene is the route to the anesthetic halothane from trichloroethylene:[5]
Iodination and bromination can be effected by the addition of
and other organic compounds.Halogenation of aromatic compounds
Aromatic compounds are subject to electrophilic halogenation:
- R−C6H5 + X2 → HX + R−C6H4−X
This kind of reaction typically works well for
Because fluorine is so reactive, other methods, such as the Balz–Schiemann reaction, are used to prepare fluorinated aromatic compounds.Other halogenation methods
In the
carbon chain is shortened by one carbon atom with respect to the carbon chain of the particular carboxylic acid. The carboxylic acid is first converted to its silver salt, which is then oxidized with halogen
:
- R−COO−Ag+ + Br2 → R−Br + CO2 + Ag+Br−
- CH3−COO−Ag+ + Br2 → CH3−Br + CO2 + Ag+Br−
Many
organometallic compounds
react with halogens to give the organic halide:
- RM + X2 → RX + MX
- CH3CH2CH2CH2Cl + LiCl
Inorganic chemistry
All
inorganic compounds is practiced on a relatively large scale is for the production of phosphorus trichloride and disulfur dichloride.[9]
See also
Wikiquote has quotations related to Halogenation.
- Dehalogenation
- Haloalkane (Alkyl halide)
- Halogenoarene(Aryl halide)
- Free radical halogenation
- Haloketone
- Electrophilic substitution
References
- ISBN 9780470771723.
- ISBN 978-3527306732.
- doi:10.1039/a900201d.
- doi:10.1039/a709063c.
- ISBN 0-444-52166-6
- ISBN 978-3527306732.
- ^ Organic chemistry by Jonathan Clayden, Nick Grieves, Stuart Warren, Oxford University Press
- doi:10.15227/orgsyn.031.0096).
{{cite journal}}
: CS1 maint: multiple names: authors list (link - ISBN 978-0-08-037941-8.