Halogenation

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(Redirected from
Chlorination reaction
)
"Fluorination" redirects here. For the addition of fluoride to drinking water, see Water fluoridation.
For the addition of chlorine, hypochlorite, etc. to drinking water, see Water chlorination.

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

million tons of bromoform and 56,000 tons of bromomethane annually.[3][clarification needed
]

The

methyl ketones
, proceeds by the free radical iodination.

Addition of halogens to alkenes and alkynes

Double-addition of
ethyne

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
bromonium ion

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]

Halothane synthesis

Iodination and bromination can be effected by the addition of

iodine number and bromine number are measures of the degree of unsaturation for fats
and other organic compounds.

Halogenation of aromatic compounds

Main article: Aryl halide

Aromatic compounds are subject to electrophilic halogenation:

R−C6H5 + X2 → HX + R−C6H4−X

This kind of reaction typically works well for

ferric chloride.[6] Many detailed procedures are available.[7][8]
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.

References

  1. ISBN 9780470771723
    .
  2. ISBN 978-3527306732
    .
  3. doi:10.1039/a900201d
    .
  4. doi:10.1039/a709063c
    .
  5. ISBN 0-444-52166-6
  6. ISBN 978-3527306732
    .
  7. ^ Organic chemistry by Jonathan Clayden, Nick Grieves, Stuart Warren, Oxford University Press
  8. doi:10.15227/orgsyn.031.0096{{cite journal}}: CS1 maint: multiple names: authors list (link
    )    .
  9. ISBN 978-0-08-037941-8
    .
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