QUESTION OF REVERSIBLE FORMATION OF BROMONIUM IONS DURING THE COURSE OF ELECTROPHILIC BROMINATION OF OLEFINS. 1. FORMAL TRANSFER OF Br + TO SCAVENGER OLEFINS FROM THE SOLVOLYTICALLY GENERATED BROMONIUM IONS OF CYCLOHEXENE AND CYCLOPENTENE.

Article abstract of DOI:10.1021/ja00328a035

trans-2-Bromo-1- left bracket ((4-bromophenyl)sulfonyl)oxy right bracket cyclohexane and -cyclopentane (1 and 2), when solvolyzed at 75 degree C in glacial acetic acid containing Br** minus and a scavenger olefin (cyclopentene for 1 and cyclohexane for 2) generate free molecular Br//2 as is evidenced by the formation of crossed products. 1 is more prone to yield crossed product than is 2. In the absence of added Br** minus , the amount of crossed product formed in the solvolysis is small. The results are interpreted in terms of competitive Br** minus capture of the intermediate bromonium ions produced during the course of solvolysis at Br** plus and carbon, the latter event leading to trans dibromide products of the starting material, while the former event generates Br//2 and olefins. The results of these experiments, when applied to electrophilic Br//2 addition to alkenes, strongly suggest that the intermediate bromonium ions are formed reversibly.