Kharasch addition

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chemical reactions for the Kharasch addition reaction of chloroform to a terminal alkene.

The Kharasch addition is an

free radical addition of CXCl3 compounds (X = Cl, Br, H) to alkenes.[1] The reaction is used to append trichloromethyl or dichloromethyl groups to terminal alkenes. The method has attracted considerable interest,[2] but it is of limited value because of narrow substrate scope and demanding conditions.[3]

The reaction mechanism involves

free radicals of the general formula CXCl2 (X = Cl, H). For the precursors carbon tetrachloride and chloroform, the requisite radicals can arise by abstraction of a halogen atom by a electropositive metal. The addition proceeds in an anti-Markovnikov fashion. Early work linked the addition to olefin polymerization. [4] This addition is a step in a protocol known as atom transfer radical polymerization.[5]

An example of Kharasch addition is the synthesis of 1,1,3-trichloro-n-nonane from

1-octene and chloroform using an iron-based catalyst:[6]

CH3(CH2)5CH=CH2 + HCCl3 → CH3(CH2)5CH(Cl)−CH2CHCl2

History

The reaction was discovered by Morris S. Kharasch in the 1940s.[7][8][9]

References

  1. ^ Name reactions: a collection of detailed reaction mechanisms, Jie Jack Li Springer; 2nd edition (September 17, 2003) 3540402039
  2. doi:10.1021/ar50089a004
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  3. ^ Foo, Klement. "The Kharasch Reaction" (PDF).
  4. doi:10.1021/ja01225a517
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  5. doi:10.1021/ja00125a035
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  6. doi:10.15227/orgsyn.045.0104
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  7. PMID 17777366
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  8. doi:10.1021/ja01197a035
    .
  9. PMID 18106035
    .
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