The reaction is named after three chemists, the German chemists Carl Magnus von Hell — and Jacob Volhard — and the Russian chemist Nikolay Zelinsky — An example of the Hell—Volhard—Zelinsky reaction being used in practice can be seen in the preparation of alanine. An approach using a Strecker synthesis  was described as "excellent but tedious"  and so an alternative starting with propionic acid was developed. In its first step, a combination of bromine and phosphorus tribromide catalyst is used to prepare 2-bromopropanoic acid ,  which is then converted to a racemic mixture of the amino acid product by ammonolysis. Unlike other halogenation reactions, this reaction takes place in the absence of a halogen carrier. The reaction is initiated by addition of a catalytic amount of PBr 3 , after which one molar equivalent of Br 2 is added.
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WordPress Shortcode. Published in: Education. Full Name Comment goes here. Are you sure you want to Yes No. Be the first to like this. No Downloads. Views Total views. Actions Shares. Embeds 0 No embeds. No notes for slide. Hell volhard-zelinski reaction 1. Defination When a carboxylic acid is treated with PBr3 and Br2 , the alpha carbon can be brominated.
A base will remove a proton from the OH group instead of from the alpha carbon, since the OH group is more acidic.
Reaction Conditions Reaction conditions are relatively harsh, involving high temperatures usually above degree C and extended reaction times. Usually less than one equivalent of P or PX3 catalyst is needed.
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Hell Volhard Zelinsky Reaction Mechanism