The peroxide effect. Free radical addition of HBr to alkenes

THE PEROXIDE EFFECT. FREE RADICAL ADDITION OF HBr TO ALKENES 

Kharasch and Mayo in 1933, in the first of many papers on the subject, showed that the addition of HBr to allyl bromide in the presence of light and air occurs rapidly to yield 1,3-dibromopropane, whereas in the absence of air and with purified reagents, the reaction is slow and 1,2-dibromopropane is formed. The latter reaction is the normal addition occurring by an ionic pathway giving the Markovnikov orientation. In 1933 the mechanism of the abnormal process ( anti-Markovnikov addition) was not discussed, and it was only in 1937 that the free radical chain mechanism for this process was proposed by Kharasch and his co-workers. The mechanism was extended to propene, for which the role of peroxides in promoting the reaction was demonstrated (equations 30, 31). This mechanism was also proposed 

Independently, at Oxford, Yoshiyuki Urushibara m the laboratory of Robert Robinson had been studying the addition of HBr to fatty acids, and had noticed the direction of addition was reversed upon exposure to the air, as reported in 1933. Initially, these authors supposed water possibly caused the effect. Urushibara became Professor at Tokyo, and continued 

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The peroxide effect. Free radical addition of HBr to alkenes... 

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