give a details account of HVZ reaction

Dear student,

When carboxylic acids react with chlorine or bromine  in the presence of red phosohorous, the alpha-hydrogen atoms are replaced by halogen atoms. It is called Hell-Volhard-Zelinsky(H.V.Z) reaction.
Ex:-
   acetic acid reacts with chlorine in presence of red phosphorus to form chloro acetic acid, dichloro acetic acid or trichloro acetic acid depending on the quantity of chlorine reacting.

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Askiitians Expert

Sagar Singh

B.Tech, IIT Delhi

sagarsingh24.iitd@gmail.com

HVZ is a reaction used to prepare alpha-halo acids. The essential condition for this reaction is the presence of alpha hydrogen. Thus Formic acid does not undergo this reaction. The reagent used is Red phosphorous/X₂   where X is a halogen. In the first step, -OH in acid group is replaced by X. On further reaction, alpha hydrogen is replaced by another X atom. On hydrolysis, the terminal X atom will be replaced by the -OH group. Thus the product obtained is alpha-halo acids.

RCH₂COOH + Br₂/P ----> RCH₂COBr  + Br₂/P ----> RCHBrCOBr + H₂O ----> RCHBrCOOH ( alpha-halo acid)