Hell-Volhard-Zelinski

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 ... 

Haworth reaction Hell-Volhard-Zelinsky reaction Hoesch reaction Hofmaim reaction. ... 

This method of a bromination of carboxylic acids is called the Hell-Volhard-Zelinsky reaction This reaction is sometimes carried out by using a small amount of phosphorus instead of phosphorus trichloride Phosphorus reacts with bromine to yield phosphorus tribromide as the active catalyst under these conditions... 

Nucleophilic substitution by ammonia on a halo acids (Section 19 16) The a halo acids obtained by halogenation of car boxylic acids under conditions of the Hell-Volhard-Zelinsky reaction are reac tive substrates in nucleophilic substitu tion processes A standard method for the preparation of a ammo acids is dis placement of halide from a halo acids by nucleophilic substitution using excess aqueous ammonia... 

Other direct methods for the sulfonation of the higher fatty acids are by the use of sulfur trioxide vapor or by the use of chlorosulfonic acid. Indirect methods are also available for the preparation of a-sulfo fatty acids and their salts from an a-bromo fatty acid made by the Hell-Volhard-Zelinsky reaction. The bromo compound may be converted directly to the sodium salt of a sulfonic acid through the Strecker reaction or may be converted to the mercaptan and oxidized to the sulfonate. Sulfonation of the lower fatty acids has been studied by Backer and co-workers. ... 

OL HALOGENATION OF CARBOXYLIC ACIDS THE HELL-VOLHARD-ZELINSKY REACTION... 

The Hell-Volhard-Zelinsky reaction is of synthetic value in that the a halogen can be displaced by nucleophilic substitution ... 

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 ... 

The a-halo acid is nonnally prepared by the Hell-Volhard-Zelinsky reaction (see Section 19.16). 

Hell-Volhard-Zelinsky reaction (Section 19.16) The phosphorus trihalide-catalyzed a halogenation of a carboxylic acid ... 

Although in the present case the amount of phosphorus used is small, equivalent amounts are often employed, particularly for the introduction of bromine, the acid bromide being produced and then substituted in the a-position. As a result, the reaction product is the bromide of the a-brominated acid which must be treated with water to convert it into the latter. Esters of the acid are often prepared from the acid bromide by the action of alcohols. (Hell-Volhard-Zelinsky process.)... 

Hell, C. Ber. Dtsch. Chem. Ges. 1881, 14, 891. Carl M. von Hell (1849-1926) was bom in Stuttgart, Germany. He studied under Fehling and Erlenmeyer. After serving in the war of 1870, he became very iU. HeU became a professor at Smttgart in 1883 where he discovered the Hell-Volhard-Zelinsky reaction. 

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. 

Hell-Volhard Zelinsky Reaction A method for forming a-halo acid. 

Problem 21.2 Synthesize leucine, (CH,),CHCH,CH(NH,)COO, by (a) Hell-Volhard-Zelinsky reaction (Section 16.3) followed by ammonolysis. (b) Gabriel synthesis, (c) phthalimidomalonic ester synthesis, (d) reductive amination of a keto acid, (e) Strecker synthesis (addition of NH, HCN to RCH=0), (/) acetylaminomalonic ester. 

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