The Addition of Halogens to Isoprene and Chloroprene

Chemistry Department, Kuwait University, Kuwait

Manuscript received 4 April 1975; accepted 21 May 1975

The reactions between bromine and chloroprene (2-chloro-1,3- butadiene), bromine and isoprene (2-methyl-1,3-butadiene) and chlorine and isoprene have been investigated.

The reaction between bromine and chloroprene goes essentially by 1,4-addition to give trans-2- ehloro-1,4-dibromo-2-butene with a small amount of 1,2- and 3,4-addition as indicated by lithium aluminum hydride reduction of the reaction products. Similar analysis of the reaction products from bromine and isoprene is complicated by allylic rearrangement of the 1,2- and 3,4-addition products to the 1,4-addition product and also by the fact that the lithium aluminum hydride reduction of both of these addition products could give 2-methyl-2-butene, the reduction product of the 1,4-addition compound. The products of the reduction consist only of those arising from the 1,2·, 3,4-and 1,4-addition compounds. No monobromo diene was obtained.

The reaction between chlorine and isoprene yields a monochloride. 2-chloromethyl,-1,3-butadiene, and both 3,4-dichloro-2-methyl-1-butene and 1,4-dirbloro-2-methyl-2-butene. These com• pounds are formed by 3,4-and 1,4-additions respectively.

The mechanistic implications of these reactions are discussed.