Question

Which of the following decolourize aqueous bromine and gives white fumes of HCl on reaction with \[{\rm{PC}}{{\rm{l}}_{\rm{5}}}\]?
A) \[{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COC}}{{\rm{H}}_{\rm{2}}}{\rm{CH}} = {\rm{C}}{{\rm{H}}_{\rm{2}}}\]
B) \[{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{3}}}\]
C) \[{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{CH}} = {\rm{CHC}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{OH}}\]
D) \[{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{OC}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{OH}}\]

Answer 1

Hint: Bromine water is a mixture produced by dissolving bromide in water. Its colour is intense yellow to red. It acts as an oxidising agent. It is useful in the organic chemistry identification of a compound that reacts with an aqueous bromine solution by the halogenation reaction mainly observed in unsaturated compounds.

Complete Step by Step Answer:
We know that unsaturated compounds are those organic compounds possessing double or triple covalent bonds such as alkenes, alkynes. There are some compounds such as phenols, enols, alkenes, glucose, etc. that undergo a reaction with bromine water. As stated above, bromine is used in the identification of an alkene. The alkene changes the colour of the bromine water to black.

In the given question, options A and C both contain a double bond. But, option A is a carbonyl compound. So, it does not give a bromine water test.
Option C is \[{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{CH}} = {\rm{CHC}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{OH}}\], It contains both double bond. Therefore, it gives a bromine water test.

The reaction with\[{\rm{PC}}{{\rm{l}}_{\rm{5}}}\] is,
\[{\rm{C}}{{\rm{H}}_{\rm{3}}} - {\rm{CH}} = {\rm{CH}} - {\rm{C}}{{\rm{H}}_{\rm{2}}} - {\rm{C}}{{\rm{H}}_{\rm{2}}} - {\rm{OH}} + {\rm{PC}}{{\rm{l}}_{\rm{5}}} \to {\rm{C}}{{\rm{H}}_{\rm{3}}} - {\rm{CH}} = {\rm{CH}} - {\rm{C}}{{\rm{H}}_{\rm{2}}} - {\rm{C}}{{\rm{H}}_{\rm{2}}} - {\rm{Cl}} + \mathop {{\rm{HCl}}}\limits_{{\rm{White}}\,{\rm{fumes}}} + {\rm{POC}}{{\rm{l}}_{\rm{3}}}\]
Therefore, option C is right.

Note: Bromine water is useful for the aldehyde functional group in an organic compound. In this reaction, the yellow coloured bromine water turns dismal yellow. The triple-bonded covalent compounds such as butyne, and ethyne can decolourise the bromine water. Therefore, bromine water is useful in the identification of unsaturated compounds. The uses of bromine as a disinfectant for spas, and swimming pools are significant. But, it is not used as a disinfectant for drinking water.