Question

complete the following reaction: 

\[\begin{array}{cc}
\phantom{...}\ce{CH3} \\
| \\
\phantom{.................}\ce{CH3-CH-COOH ->[(i) Br2/Red P4][(ii)H2O]}
\end{array}\]

Answer 1

Carboxylic acid having a-hydrogen are halogenated at a-position on treatment with 2 Br in presence of red phosphorous to give a -halocarboxylic acids. This is the HeII-Volhard-Zelinsky reaction.  
\[\begin{array}{cc}
\phantom{.................}\ce{CH3}
\phantom{...........................}\ce{CH3}\\
\phantom{...............}|
\phantom{..............................}| \\
\phantom{.................}\ce{CH3-CH-COOH ->[(i) Br2/Red P4][(ii)H2O]CH3-C-COOH}\\
\phantom{.............................................} | \\
\phantom{..............................................} \ce{Br}
\end{array}\]