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 basic reaction proceeds through the CXCl2 free radical. Examples of organohalides are carbon tetrachloride and chloroform. Radicals are often generated by abstraction of a halide radical by a metal ion. The addition is an anti-Markovnikov addition. Early work linked the addition to olefin polymerization [4] and is therefore considered a first step into what was to become atom transfer radical polymerization.
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.[5]
The reaction was discovered by Morris S. Kharasch in the 1940s.[6][7][8]