Rearrangement in the solvolysis of 3-bromopentane in 60% aqueous ethanol

Abstract

Isomerically pure 3-bromopentane has been prepared from tri-1-ethylpropyl phosphite and hydrogen bromide and solvolysed in 60% aqueous ethanol. The detection of about 1% rearrangement products in both acid and weakly alkaline conditions supports the view that carbonium ion intermediates are formed in the reaction of at least a proportion of the molecules. The formation of 2-bromopentane is attributed to internal return in a close ion-pair and accounts for some, if not all, of the rearranged substitution products. No rearrangement occurs under more strongly alkaline conditions. The results are discussed in relation to previous work on s-alkyl bromides and s-alkyl sulphonates.