Method used for separation of mixture of products (B and C) obtained in the following reaction is [figure]
- simple distillation
- sublimation
- fractional distillation
- steam distillation
Answer
(3) fractional distillation
Solution
Bromination of benzene in the presence of FeBr3 gives bromobenzene (A).
–Br is an ortho/para-directing group, so nitration of A gives a mixture of o-bromonitrobenzene (B) and p-bromonitrobenzene (C):
[figure]
B and C are position isomers with boiling points very close to each other (about 261 °C and 256 °C).
As per NCERT, if the difference in boiling points of two liquids is not much, simple distillation cannot be used to separate them; such liquids are separated by fractional distillation, in which the vapours pass through a fractionating column.
Steam distillation is not suitable because neither isomer has an intramolecular hydrogen bond (as in o-nitrophenol) that would make only one of them steam volatile; sublimation is also not applicable.
Answer: (3)