what is hell volhard zelinsky (HVZ) reaction?

Question

related to carboxylic acids. give reaction and mechanism.

Answer 1

HVZ reaction is the replacement of an alpha-hydrogen by a halogen on reaction with 'Red Phosphrous+ Br2 / Cl2'.
reacn:
R-CH2-COOH + Red P+ Br-Br (Br2)------------------> R-CH(Br)-COOH


in case Br2 is present in excess , then all alpha hydrogen gets replaced.So:

R-CH2-COOH + Red P+ Br-Br (Br2) (excess)------------------> R-C(Br2)-COOH

Answer 2

Hell Volhard Zelinsky Reaction

Answer 3

The Hell-Volhard-Zelinsky halogenation reaction halogenates carboxylic acids at the α carbon.

Typically, a carboxylic acid is first reacted with PBr3 and Br2. The PBr3 replaces the OH group of the carboxylic acid with a bromine, resulting in a carboxylic acid bromide. The acid bromide can then tautomerize to an enol, which will readily react with the Br2 to brominate the molecule a second time at the α position. The first step thus results in a carboxylic acid bromide which is also brominated at the α position.

In a second step, the carboxylic acid may be recovered by reacting the carboxylic acid bromide with water or a weak aqueous acid. This results in the hydrolysis of the acid bromide, i.e. the displacement of the bromine directly bound to the carbonyl group by an OH group. (The hydrolysis is an example of a nucleophilic acyl substitution.)

The final product is thus the original carboxylic acid brominated at the α position.

Answer 4

Halogenation of carboxylic acids ..
Here the alpha hydrogen is substituted by the halogen

Answer 5

a-Halogenation of carboxylic acids in the presence of catalytic phosphorus, presumably involving the enol form of the
intermediate acyl halide:


R-COOH+Br2 = R-COBr+Br2 = R-CBr-COBr+H2O =
R-CBr-COOH

Answer 6

I believe its Br2, PBr3, and water.

Answer 7

I CAN'T GIVE U THE CORRECT ANSWER. BUT I THINK IT WUD BE IN THE 12th std CHEMISTRY TEXT BOOK.