Kharasch addition
The Kharasch addition is an organic reaction and a metal-catalysed free radical addition of CXCl3 compounds (X = Cl, Br, H) to alkenes.Name reactions: a collection of detailed reaction mechanisms, Jie Jack Li Springer; 2nd edition (September 17, 2003) 3540402039 The reaction is used to append trichloromethyl or dichloromethyl groups to terminal alkenes. The method has attracted considerable interest,{{cite journal |doi=10.1021/ar50089a004|title=Free-radical additions to olefins in the presence of redox systems |year=1975 |last1=Minisci |first1=Francesco |journal=Accounts of Chemical Research |volume=8 |issue=5 |pages=165–171 }} but it is of limited value because of narrow substrate scope and demanding conditions.{{cite web |last1=Foo |first1=Klement |title=The Kharasch Reaction |url=https://www.scripps.edu/baran/images/grpmtgpdf/Foo_Nov_10.pdf}}
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. {{Cite journal| doi = 10.1021/ja01225a517| year = 1945| last1 = Kharasch | first1 = M. S.| title = Addition of Derivatives of Chlorinated Acetic Acids to Olefins| last2 = Urry | first2 = W. H.| last3 = Jensen | first3 = E. V.| journal = Journal of the American Chemical Society| volume = 67| issue = 9| pages = 1626 }} This addition is a step in a protocol known as atom transfer radical polymerization.{{Cite journal|doi=10.1021/ja00125a035|year = 1995| last1 = Wang | first1 = J.S.| title = Controlled/"Living" Radical Polymerization. Atom Transfer Radical Polymerization in the Presence of Transition-Metal Complexes.| last2 = Matyjaszewski | first2 = K.| journal = Journal of the American Chemical Society| volume = 117| issue = 20| pages = 5614 }}
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:{{cite journal|journal=Organic Syntheses|volume=45|page=104| year=1965|title=1,1,3-Trichlorononane| doi=10.15227/orgsyn.045.0104| author=D. Vofsi, M. Asscher}}
:{{chem2|CH3(CH2)5CH\dCH2 + HCCl3 -> CH3(CH2)5CH(Cl)\sCH2CHCl2}}
History
The reaction was discovered by Morris S. Kharasch in the 1940s.{{Cite journal| doi = 10.1126/science.102.2640.128| pmid = 17777366| year = 1945| last1 = Kharasch | first1 = M.| last2 = Jensen | first2 = E.| last3 = Urry | first3 = W.| title = Addition of Carbon Tetrachloride and Chloroform to Olefins| volume = 102| issue = 2640| pages = 128| journal = Science |bibcode = 1945Sci...102..128K }}{{Cite journal| doi = 10.1021/ja01197a035| year = 1947| last1 = Kharasch | first1 = M. S.| title = Reactions of Atoms and Free Radicals in Solution. X. The Addition of Polyhalomethanes to Olefins| last2 = Jensen | first2 = E. V.| last3 = Urry | first3 = W. H.| journal = Journal of the American Chemical Society| volume = 69| issue = 5| pages = 1100–1105 }}{{Cite journal| doi = 10.1021/jo01164a020| pmid = 18106035| year = 1948| last1 = Kharasch | first1 = M. S.| last2 = Kuderna | first2 = B. M.| last3 = Urry | first3 = W.| title = Reactions of atoms and free radicals in solution; the additions of bromodichloromethane and dibromodichloromethane to olefins; the preparation of 2-alkenals| journal = Journal of Organic Chemistry| volume = 13| issue = 6| pages = 895–902 }}