alleryThe **Hell–Volhard–Zelinsky (HVZ) reaction** converts a carboxylic acid (with $\alpha$-H) to an $\alpha$-halo acid using
A$NaOBr$
B$Br_2$ with red phosphorus
C$Cl_2$ with $hv$
D$KMnO_4$
Answer & Solution
Correct answer: B. $Br_2$ with red phosphorus
$RCH_2COOH + Br_2 \xrightarrow{red\,P} RCHBrCOOH + HBr$.
Red P generates $PBr_3$ which converts the acid to acyl bromide
the $\alpha$-position then enolises and brominates.
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