Kharasch addition explained

The Kharasch addition is an organic reaction and a metal-catalysed 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]

History

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

Notes and References

1. Name reactions: a collection of detailed reaction mechanisms, Jie Jack Li Springer; 2nd edition (September 17, 2003) 3540402039
2. 10.1021/ar50089a004. Free-radical additions to olefins in the presence of redox systems . 1975 . Minisci . Francesco . Accounts of Chemical Research . 8 . 5 . 165–171 .
3. Web site: Foo . Klement . The Kharasch Reaction .
4. 10.1021/ja01225a517. 1945. Kharasch . M. S.. Addition of Derivatives of Chlorinated Acetic Acids to Olefins. Urry . W. H.. Jensen . E. V.. Journal of the American Chemical Society. 67. 9. 1626 .
5. 10.1021/ja00125a035. 1995. Wang . J.S.. Controlled/“Living” Radical Polymerization. Atom Transfer Radical Polymerization in the Presence of Transition-Metal Complexes.. Matyjaszewski . K.. Journal of the American Chemical Society. 117. 20. 5614 .
6. Organic Syntheses. 45. 104. 1965. 1,1,3-Trichlorononane. 10.15227/orgsyn.045.0104. D. Vofsi, M. Asscher.
7. 10.1126/science.102.2640.128. 17777366. 1945. Kharasch . M.. Jensen . E.. Urry . W.. Addition of Carbon Tetrachloride and Chloroform to Olefins. 102. 2640. 128. Science . 1945Sci...102..128K .
8. 10.1021/ja01197a035. 1947. Kharasch . M. S.. Reactions of Atoms and Free Radicals in Solution. X. The Addition of Polyhalomethanes to Olefins. Jensen . E. V.. Urry . W. H.. Journal of the American Chemical Society. 69. 5. 1100–1105 .
9. 10.1021/jo01164a020. 18106035. 1948. Kharasch . M. S.. Kuderna . B. M.. Urry . W.. Reactions of atoms and free radicals in solution; the additions of bromodichloromethane and dibromodichloromethane to olefins; the preparation of 2-alkenals. Journal of Organic Chemistry. 13. 6. 895–902 .