# Reason behind conversion of acid to acid bromide in Hell-Volhard-Zelinsky reaction [closed]

Why in Hell-Volhard-Zelinsky (HVZ) reaction the acid is first converted to acid bromide by using $\ce{PBr3}$ and then alpha halogenation is carried out?

• How do you think the alpha-bromine is incorporated into the acyl bromide? Homework??? – user55119 Feb 14 '18 at 15:23
• Google is your friend! – Waylander Feb 14 '18 at 15:38

The $\alpha$ halogenation occurs through the enol form.
The formation of the acyl halide is key because carboxylic acids do not form enols readily since carboxylic acid proton is removed before the $\alpha$ hydrogen. Acyl halides lack the carboxylic acid hydrogen.
The halogenation is performed by the $\ce{X2}$, either bromine or chlorine. When $\ce{PBr3}$ and $\ce{Cl2}$ is used, the alpha-chloro acid is obtained and not the bromo acid.