Hell-Volhard-Zelinsky process

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.)... 

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... 

Slavish adherence to this dictum could lead to ridiculous names. We hope that if anyone discovers a photo-Hell-Volhard-Zelinsky reaction he will have the good sense to find a better name for the process. 

The bromine is introduced onto the a-carbon by treating the carboxylic acid with Br2 and a catalytic amount of PBr, in a process known as the Hell-Volhard-Zelinsky reaction. This reaction proceeds through an enol intermediate. Because carboxylic acids form enols only with difficulty, a catalytic amount of PBr3 is added to form a small amount of the acyl bromide, which enolizes more readily than the acid. Addition of bromine to the enol produces an a-bromoacyl bromide (see Section 20.2). This reacts with a molecule of the carboxylic acid in a process that exchanges the Br and OH groups to form the... 

It is both a pleasure and a privilege to have been invited to write the Foreword to a book of such importance as Dr. Comyns dictionary of named processes in the chemical industry. For many years, chemists have had access to books with titles like Named Reactions in Organic Chemistry. Here the busy student or researcher can discover immediately the nature of the Wurtz reaction, the Cannizzaro reaction, and such curiosities as the Hell-Volhard-Zelinsky reaction. Until the first edition of the present book appeared in 1993, no such literary assistance was available to the multitudes who labored in the chemical industry. Six years later, a second edition took into account the many novelties that had appeared in that short period. Now a third edition is expanded still further, particularly by inclusion of many biological processes that industry now uses. 

Haworth Methylation Haworth Phenanthrene Synthesis Hayashi Rearrangement Heck Reaction Helferich Method Hell-Volhard-Zelinsky Reaction Henkel Process Henkel Reaction Henry Reaction... 

This process, called the Hell-Volhard-Zelinski reaction, is believed to occur via the following sequence of events ... 

Consider a process that attempts to prepare tyrosine using a Hell-Volhard-Zelinski reaction ... 

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