Which of the following reactions involves $\alpha$ -halogenation of carboxylic acid?
Which of the following reactions involves $\alpha$ -halogenation of carboxylic acid?
Gattermann reaction
Riemer - Tiemann reaction
Sandmeyer reaction
Hell-Vohlard-Zelinsky reaction
Solution
Hell Volhard Zelinsky (HVZ) reaction:
This reaction involves alpha bromination of carboxylic acids. Carboxylic acids react with chlorine or bromine in presence of small amount of red phosphorous to give alpha halo carboxylic acids.
$\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{COOH} \stackrel{\mathrm{Br}_{2} / \mathrm{P}}{\rightarrow} \mathrm{CH}_{3}-\mathrm{CHBr}-\mathrm{COOH} \stackrel{\mathrm{Br}_{2} / \mathrm{P}}{\rightarrow} \mathrm{CH}_{3}-\mathrm{CBr}_{2}-$
$\mathrm{COOH} \stackrel{\mathrm{Br}_{2} / \mathrm{P}}{\longrightarrow}$ No further reaction.