Hell-Volhard-Zelinsky chlorination

The conversion of an aliphatic carboxylic acid into the a-bromo- (or a-chloro ) acid by treatment with bromine (or chlorine) in the presence of a catal3rtic amount of phosphorus tribromide (or trichloride) or of red phosphorus is known as the Hell-Volhard-Zelinsky reaction. The procedure probably involves the intermediate formation of the acyl halide, since it is known that halogens react more rapidly with acyl haUdes than with the acids themselves ... 

Section 19.16 Halogenation at the a-carbon atom of carboxylic acids can be accomplished by the Hell-Volhard-Zelinsky reaction. An acid is treated with chlorine or bromine in the presence of a catalytic quantity of phosphorus or a phosphorus trihalide ... 

Carboxylic acids having an a-hydrogen are halogenated at the a-position on treatment with chlorine or bromine in the presence of small amount of red phosphorus to give a-halocarboxylic acids. The reaction is known as Hell-Volhard-Zelinsky reaction. 

Chlorination must precede esterification, because the Hell-Volhard-Zelinsky reaction requires a carboxylic acid, not an ester, as the starting material. The remaining step is a nucleophilic substitution reaction. 

OL-Chlorination of carboxylic acids.2 A Hell-Volhard-Zelinsky type of a-chlori-nation of carboxylic acids with chlorosulfonic acid is possible if a competing free radical chlorination is suppressed. For this purpose, 1 is superior to oxygen 3 in addition, the reaction is applicable to both short- and long-chain acids (equation I). 

In the presence of a small amount of phosphorus, aliphatic carboxylic acids react smoothly with chlorine or bromine to yield a compound in which a-hydrogen has been replaced by halogen. This is the Hell-Volhard-Zelinsky reaction. Because of its specificity—only alpha halogenation-- the readiness with which it takes place, it is of considerable importance in synthesis. 

Chlorine is introdnced at the a-carbon atom of a carboxylic acid. The reaction is catalyzed by a small amonnt of phosphorns or a phosphorns trihalide and is called the Hell-Volhard-Zelinsky reaction. 

At this point, only an amino (NH2) group need be added, alpha to the carboxyl group to obtain alanine. To do this, first add a halogen, either Br or Cl, to the alpha position. This can be accomplished using the Hell-Volhard-Zelinsky reaction. This reaction results in a-halo acids. The carboxylic acid is reacted with a halogen (bromine or chlorine) in the presence of catalytic amounts of phosphorus trihalide. Hence,... 

Carboxylic acids bearing a hydrogen atoms react with bromine or chlorine in the presence of phosphorus (or a phosphorus halide) to give a-halo carboxylic acids through a reaction known as the Hell-Volhard-Zelinski (or HVZ) reaction. 

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