Carboxylic Acids And Its Derivatives

Identify the name of the reaction involved in conversion of $A \rightarrow B$ and name the compound $B$.

\(\mathrm{CH}_3 \mathrm{CN} \xrightarrow[\mathrm{H}_2 \mathrm{O}]{\mathrm{H}^{+}} \mathrm{A}-\xrightarrow[\mathrm{H}^{+} / \mathrm{H}_2 \mathrm{O}]{\mathrm{Cl}_2 / \text { Red Phosphorous }} \mathrm{B}\)