Question

Which reagent is used for the bromination of methyl phenyl ether?
A) $\text{B}{{\text{r}}_{\text{2}}}\text{/C}{{\text{H}}_{\text{3}}}\text{COOH}$
B) $\text{B}{{\text{r}}_{\text{2}}}\text{/ Red P}$
C) $\text{B}{{\text{r}}_{\text{2}}}\text{/ FeB}{{\text{r}}_{\text{3}}}$
D) $\text{HBr / Heat}$

Answer 1

Hint:
Bromination of organic compounds is done by a number of reagents which include bromine and red phosphorous, bromine and iron bromide, and hydrobromic acid and the reagent that is applicable depends on the type of the reactant.

Complete step by step solution:
Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine or brominated compounds. For the bromination of methyl phenyl ether, a combination of bromine and Ferric Bromide is used. The presence of alkoxy group in aromatic ethers activates the aromatic ring towards electrophilic substitution reaction. Two products are obtained from the reaction, one is the para product and the other is the ortho product because the alkoxy group is an op-orienting group. The para isomer is obtained in 90% yield due to the resonance stabilized structure.
Therefore, the correct answer is $\text{B}{{\text{r}}_{\text{2}}}\text{/ FeB}{{\text{r}}_{\text{3}}}$, bromine and ethanoic or acetic acid, option C.

Note:
The Ferric Bromide here acts as the Lewis acid and accepts the electron pair from bromine, making it more electrophilic in nature to enhance the rate of the reaction. There are different other such electrophilic substitution reactions of the arenes or the aromatic compounds. The brominated product acts as the intermediate of different reaction processes. But bromine itself is very dangerous to handle as elemental bromine is a strong irritant and is hazardous. Therefore the use and handling of bromine needs major precautions. Even in low quantities bromine vapour can cause breathing disorders and damage to the mucous membrane.