Question

Which reaction is used for the preparation of \[\alpha \] -Bromoacetic acid?
A. Kolbe's Reaction
B. Reimer- Tiemann Reaction
C. Hell volhard reaction
D. Perkins Reaction

Answer 1

Hint: The chemical compound named \[\alpha \] -Bromoacetic acid is obtained from the carboxylic acid. Its chemical formula is \[{\rm{Br}}{{\rm{H}}_{\rm{2}}}{\rm{C}} - {\rm{CO}} - {\rm{OH}}\] . In this compound, bromine is bonded to alpha carbon.

Complete step by step answer:
Let's discuss all the options given in the question.
First, we will understand what Kolbe's reaction is. Kolbe's reaction is the conversion of phenol into salicylic acid. In the first step, phenol is converted into phenoxide ion by reacting it with sodium hydroxide. In the second step, the reaction of phenoxide ions with carbon dioxide in an acidic medium gives salicylic acid.

Image: Kolbe’s reaction

Therefore, option A is wrong.

 In Riemer-Tiemann reaction, phenol to salicylaldehyde conversion takes place by reacting phenol with chloroform along with sodium hydroxide.




Image: Riemer-Tiemann reaction

Therefore, option B is wrong.
Let's understand option D, that is, Perkin's reaction. In this reaction, an aliphatic acid anhydride, an aromatic aldehyde, and an alkali salt of the acid undergo a reaction to give cinnamic acid derivatives. The product obtained is \[\alpha ,\beta \]unsaturated aromatic acid. Hence, option D is wrong.
Let's understand the Hell Volhard reaction in detail. In this reaction, carboxylic acid undergoes reaction with \[{\rm{C}}{{\rm{l}}_{\rm{2}}}\]or \[{\rm{B}}{{\rm{r}}_{\rm{2}}}\] in the presence of red coloured phosphorus to gives \[\alpha \]-chloroacetic acid or
 \[\alpha \]-bromoacetic acid. Here, one hydrogen atom of alpha carbon gets replaced by an atom of chlorine or bromine.
\[{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH}} + {\rm{B}}{{\rm{r}}_{\rm{2}}} \overset{Red Phosphorus}{\rightarrow} \mathop {{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{BrCOOH}}}\limits_{{\rm{\alpha - Bromoacetic}}\,{\rm{acid}}} \]

Hence, option C is right.

Note: It is to be noted that, in organic chemistry, the \[\alpha \] carbon indicates the first carbon atom that is bonded to the carbonyl group and the \[\beta \] carbon indicates that carbon atom which comes in the second position from the carbonyl carbon.