This reaction is called Hell-Volhard-Zelinsky $(HVZ)$ reduction. This reaction is example of $\alpha -H-$substitution.
$C{{H}_{3}}C{{H}_{2}}COOH\,\xrightarrow[-\,HBr]{B{{r}_{2}}/P}$ $\begin{matrix}
\begin{matrix}
Br \\
| \\
\end{matrix}\,\,\,\,\,\, \\
C{{H}_{3}}-C-COOH \\
|\,\,\,\,\,\,\, \\
Br\,\,\,\, \\
\end{matrix}$

ઉપરની પ્રક્રિયામાં $Y$ શું છે ?

$\underset{1}{\mathop{\begin{matrix}
O\,\,\,\,\,\,\,\,\,\,\,\, \\
||\,\,\,\,\,\,\,\,\,\,\,\,\, \\
C{{H}_{3}}COCHC{{H}_{3}} \\
\end{matrix}}}\,$ $\underset{2}{\mathop{\begin{matrix}
\,\,\,\,O \\
\,\,\,\,|| \\
C{{H}_{3}}CCl \\
\end{matrix}}}\,$ $\underset{3}{\mathop{\begin{matrix}
O\,\,\,\,\,\,\,\,\, \\
||\,\,\,\,\,\,\,\,\, \\
C{{H}_{3}}CNHC{{H}_{3}} \\
\end{matrix}}}\,$


