Hell–Volhard–Zelinsky halogenation
chemical reaction
The Hell–Volhard–Zelinsky halogenation reaction is a chemical transformation that transforms an alkyl carboxylic acid to the α-bromo derivative. It is a specialized and rare kind of halogenation.
Examples
An example of the Hell–Volhard–Zelinsky reaction can be seen in the preparation of alanine from propionic acid. In the first step, a combination of bromine and phosphorus tribromide (catalyst) is used in the Hell–Volhard–Zelinsky reaction to prepare 2-bromopropionic acid, which in the second step is converted to a racemic mixture of the amino acid product by ammonolysis.
Mechanism
The reaction is initiated by addition of a catalytic amount of PBr3, after which one molar equivalent of Br2 is added. PBr3 converts the carboxylic OH to the acyl bromide. The acyl bromide tautomerizes to an enol, which reacts with the Br2 to brominate at the α position. In neutral to slightly acidic aqueous solution, hydrolysis of the α-bromo acyl bromide occurs spontaneously, yielding the α-bromo carboxylic acid. If an aqueous solution is desirable, a full molar equivalent of PBr3 must be used as the catalytic chain is disrupted.
If little nucleophilic solvent is present, reaction of the α-bromo acyl bromide with the carboxylic acid yields the α-bromo carboxylic acid and regenerates the acyl bromide intermediate.
The public source identifies “Hell–Volhard–Zelinsky halogenation” as chemical reaction. This brief keeps that definition visible, then builds a research path around Hell, Volhard and Zelinsky.
Why this record matters
A short description can identify a subject without explaining its stakes. For “Hell–Volhard–Zelinsky halogenation”, the useful work is to connect “chemical reaction” to the records capable of establishing context and consequence.
The date and method of observation matter as much as the stated conclusion, especially where classification or consensus has changed. The source revision retrieved here is dated Jun 26, 2025. The linked authority identifier is Q902219. None of the 0 selected statements returned an explicit reference.
A general summary may omit uncertainty, sample limits or methodological disagreement that is explicit in the technical record. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Check terminology, classification and the date of the cited evidence. Scientific names and technical consensus can change while older records retain historical value.
- Current terminology
- Classification context
- Finding cited technical literature
Primary datasets, specimen catalogues, standards bodies and the most recent peer-reviewed literature.
Three-step research path
- Establish the record: confirm the title “Hell–Volhard–Zelinsky halogenation”, its source revision and the description used here.
- Expand the search: follow Hell–Volhard–Zelinsky halogenation primary sources, Hell–Volhard–Zelinsky halogenation archive and Hell research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “Hell–Volhard–Zelinsky halogenation”?
- Is the terminology current, historical or disputed?
- Has classification or technical consensus changed since the cited source?
Search terms from this dossier
This entry incorporates text from “Hell–Volhard–Zelinsky halogenation” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.