The given reaction is an example of the Hell-Volhard-Zelinsky (HVZ) reaction, which selectively brominates the $\alpha$-carbon of carboxylic acids in the presence of Br$_2$ and red phosphorus. The reaction mechanism involves the formation of an $\alpha$-brominated carboxylic acid.
\[\text{COOH} \xrightarrow{\text{Br}_2/\text{Red P}} \text{COOH-Br} \xrightarrow{\text{H}_2\text{O}} \text{COOH-Br (Product)}\]
Thus, the product formed is the $\alpha$-bromo derivative of the given carboxylic acid.
Give reasons for the following:
Benzoic acid does not undergo Friedel-Crafts reaction.
(b) HCHO is more reactive than $CH_3\text{CHO towards addition of HCN}$
(c) Vinyl group directly attached with carboxylic acid should decrease the acidity of corresponding carboxylic acid due to resonance, but on the contrary it increases the acidity.
In the given reaction sequence, the structure of Y would be: