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]
- CH3(CH2)5CH=CH2 + HCCl3 → CH3(CH2)5CH(Cl)−CH2CHCl2
History
editThe reaction was discovered by Morris S. Kharasch in the 1940s.[7][8][9]
References
edit- ^ Name reactions: a collection of detailed reaction mechanisms, Jie Jack Li Springer; 2nd edition (September 17, 2003) 3540402039
- ^ Minisci, Francesco (1975). "Free-radical additions to olefins in the presence of redox systems". Accounts of Chemical Research. 8 (5): 165–171. doi:10.1021/ar50089a004.
- ^ Foo, Klement. "The Kharasch Reaction" (PDF).
- ^ Kharasch, M. S.; Urry, W. H.; Jensen, E. V. (1945). "Addition of Derivatives of Chlorinated Acetic Acids to Olefins". Journal of the American Chemical Society. 67 (9): 1626. doi:10.1021/ja01225a517.
- ^ Wang, J.S.; Matyjaszewski, K. (1995). "Controlled/"Living" Radical Polymerization. Atom Transfer Radical Polymerization in the Presence of Transition-Metal Complexes". Journal of the American Chemical Society. 117 (20): 5614. doi:10.1021/ja00125a035.
- ^ D. Vofsi, M. Asscher (1965). "1,1,3-Trichlorononane". Organic Syntheses. 45: 104. doi:10.15227/orgsyn.045.0104.
- ^ Kharasch, M.; Jensen, E.; Urry, W. (1945). "Addition of Carbon Tetrachloride and Chloroform to Olefins". Science. 102 (2640): 128. Bibcode:1945Sci...102..128K. doi:10.1126/science.102.2640.128. PMID 17777366.
- ^ Kharasch, M. S.; Jensen, E. V.; Urry, W. H. (1947). "Reactions of Atoms and Free Radicals in Solution. X. The Addition of Polyhalomethanes to Olefins". Journal of the American Chemical Society. 69 (5): 1100–1105. doi:10.1021/ja01197a035.
- ^ Kharasch, M. S.; Kuderna, B. M.; Urry, W. (1948). "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. doi:10.1021/jo01164a020. PMID 18106035.