Question

How will you convert n-propyl bromide to isopropyl bromide?

Answer 1

To convert n-propyl bromide to isopropyl bromide, you must perform a two-step reaction sequence involving an elimination followed by an addition.

1. Dehydrohalogenation of n-Propyl Bromide to Propene: In the first step, n-propyl bromide (1-bromopropane) is treated with a strong base, such as alcoholic potassium hydroxide (KOH), to undergo a beta-elimination reaction (E2). This removes a hydrogen and a bromine atom to form a double bond, yielding propene.
   \[\ce{\underset{n-propyl bromide}{CH3 - CH2 - CH2 - Br} + KOH(alc) -> \underset{propene}{CH3 - CH = CH2} + KBr + H2O}\]
2. Addition of HBr to form isopropyl bromide: In the second step, the propene intermediate is reacted with hydrogen bromide (HBr). The addition of HBr to an unsymmetrical alkene follows Markovnikov’s rule. According to Markovnikov’s rule, the hydrogen atom adds to the carbon atom of the double bond that has more hydrogen atoms, and the bromine atom adds to the carbon atom with fewer hydrogen atoms.
   \[\ce{\underset{propene}{CH3 - CH = CH2} + HBr -> \underset{isopropyl bromide}{CH3 - CH (Br)CH3}}\]