World Library  
Flag as Inappropriate
Email this Article

Aryl halide

Article Id: WHEBN0000648787
Reproduction Date:

Title: Aryl halide  
Author: World Heritage Encyclopedia
Language: English
Subject: Organohalides, Richard F. Heck, Molecular modification, Aromatic compounds, Grignard reaction
Publisher: World Heritage Encyclopedia

Aryl halide

In aromatic ring are replaced by a halide. The haloarene are distinguished from haloalkanes because they exhibit many differences in methods of preparation and properties. The most important members are the aryl chlorides, but the class of compounds is so broad that many derivatives enjoy niche applications.


  • Preparation 1
    • Direct halogenation 1.1
    • Sandmeyer, Schiemann and Gatterman reactions 1.2
    • Halogenation in nature 1.3
  • Structural trends 2
  • Reactions 3
    • Biodegradation 3.1
  • Applications 4
  • References 5


The two main preparatory routes to aryl halides are direct halogenation and via diazonium salts.[1]

Direct halogenation

In the Friedel-Crafts halogenation, Lewis acids serve as catalysts. Many metal chlorides are used, examples include iron(III) chloride or aluminium chloride. The most important aryl halide, chlorobenzene is produced by this route. Monochlorination of benzene is always accompanied by formation of the dichlorobenzene derivatives.[2]

Arenes with electron donating groups react with halogens even in the absence of Lewis acids. For example, phenols and anilines react quickly with chlorine and bromine water to give multiple halogenated products.[3] The decolouration of bromine water by electron-rich arenes is used in the bromine test.

Direct halogenation of arenes are possible in the presence of light or at high temperature. For alkylbenzene derivatives, the alkyl positions tend to be halogenated first in the free radical halogenation. To halogenate the ring, Lewis acids are required, and light should be excluded to avoid the competing reaction.[1]

Reaction between benzene and halogen to form an halogenobenzene

Sandmeyer, Schiemann and Gatterman reactions

The second main route is the Sandmeyer reaction. Anilines (aryl amines) are converted to their diazonium salts using nitrous acid. For example, copper(I) chloride converts diazonium salts to the aryl chloride. Nitrogen gas is the leaving group, which makes this reaction very favorable. The similar Schiemann reaction uses the tetrafluoroborate anion as the fluoride donor. Gatterman Reaction can also be used to convert Diazonium salt to chlorobenzene or bromobenzene by using copper powder instead of copper chloride or copper bromide. But this must be done in the presence of HCl and HBr respectively.

Halogenation in nature

Aryl halides occur widely in nature, most commonly produced by marine organisms that utilize the chloride and bromide in ocean waters. Chlorinated and brominated aromatic compounds are also numerous, e.g. derivatives of tyrosine, tryptophan, and various pyrrole derivatives. Some of these naturally occurring aryl halides exhibit useful medicinal properties.[4][5]

Vancomycin, an important antibiotic, is an aryl chloride isolated from soil fungi.
The chemical structure of 6,6′-dibromoindigo, the main component of Tyrian Purple

Structural trends

The C-X distances for aryl halides follow the expected trend. These distances for fluorobenzene, chlorobenzene, bromobenzene, and methyl 4-iodobenzoate are 135.6(4), 173.90(23), 189.8(1), and 209.9 pm, respectively.[6]


Aryl halides do not participate in conventional SN2 nucleophilic aromatic substitution reactions. Instead the halides are displaced by strong nucleophiles via reactions involving radical anions. Alternatively aryl halides, especially the bromides and iodides, undergo oxidative addition, and thus are subject to Buchwald–Hartwig amination-type reactions.

Aryl halides react with metals to give more reactive derivatives that behave as sources of aryl anions. Magnesium aryl halides are organic synthesis of other aryl compounds.

Chlorobenzene was once the precursor to phenol, which is now made by oxidation of cumene. At high temperatures, aryl groups react with ammonia to give anilines.[2]


Rhodococcus phenolicus is a bacterium species able to degrade dichlorobenzene as sole carbon sources.[7]


The aryl halides produced on the largest scale are chlorobenzene and the isomers of dichlorobenzene. One major but discontinued application was the use of chlorobenzene as a solvent for dispersing the herbicide Lasso. Overall, production of aryl chlorides as well as related naphthyl derivatives has been declining since the 1980s, in part due to environmental concerns.[2] Triphenylphosphine is produced from chlorobenzene:

3 C6H5Cl + PCl3 + 6 Na → P(C6H5)3 + 6 NaCl

Aryl bromides are widely used as fire-retardants. The most prominent member is tetrabromobisphenol-A, which is prepared by direct bromination of the diphenol.[8]


  1. ^ a b Boyd, Robert W.; Morrison, Robert (1992). Organic chemistry. Englewood Cliffs, N.J: Prentice Hall. p. 947.  
  2. ^ a b c Beck, U.; Löser, E. (2011). "Chlorinated Benzenes and Other Nucleus-Chlorinated Aromatic Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry.  
  3. ^ Illustrative procedure for chlorination of an aromatic compound: Edward R. Atkinson, Donald M. Murphy, and James E. Lufkin (1951). "dl-4,4',6,6'-Tetrachlorodiphenic Acid".  
  4. ^ Fujimori, Danica Galonić; Walsh, Christopher T. (2007). "What's new in enzymatic halogenations". Current Opinion in Chemical Biology 11 (5): 553–60.  
  5. ^ Gribble, Gordon W. (2004). "Natural Organohalogens: A New Frontier for Medicinal Agents?". Journal of Chemical Education 81 (10): 1441.  
  6. ^ Oberhammer, Heinz (2009). "PATai's Chemistry of Functional Groups".  
  7. ^ Rehfuss, Marc; Urban, James (2005). "Rhodococcus phenolicus sp. nov., a novel bioprocessor isolated actinomycete with the ability to degrade chlorobenzene, dichlorobenzene and phenol as sole carbon sources". Systematic and Applied Microbiology 28 (8): 695–701.  
  8. ^ Ioffe, D.; Kampf, A. (2002). "Bromine, Organic Compounds". Kirk-Othmer Encyclopedia of Chemical Technology.  .
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.