# N-Bromosuccinimide
**N-Bromosuccinimide** (NBS) is a crystalline organic brominating reagent, a five-membered cyclic dicarboximide carrying a bromine atom on its nitrogen, used chiefly for selective bromination at allylic and benzylic positions and as a mild source of electrophilic bromine.[1](https://pubchem.ncbi.nlm.nih.gov/compound/N-Bromosuccinimide) Its systematic name is 1-bromopyrrolidine-2,5-dione (also called N-bromobutanimide), and it is the most commonly used of the N-bromoamide reagents in synthetic organic chemistry.[1](https://pubchem.ncbi.nlm.nih.gov/compound/N-Bromosuccinimide) • [2](https://pmc.ncbi.nlm.nih.gov/articles/PMC13385683/)
| Key fact | Detail |
|---|---|
| Identity | Five-membered cyclic dicarboximide, bromo substituent on nitrogen; formula C4H4BrNO2, molecular weight 177.98 g/mol, CAS 128-08-5[1](https://pubchem.ncbi.nlm.nih.gov/compound/N-Bromosuccinimide) |
| Physical form | Crystalline solid; melting point 176 °C (dec.) per supplier data[3](https://www.tcichemicals.com/US/en/p/B0656) |
| Signature reaction | Allylic and benzylic bromination (the Wohl–Ziegler reaction) with light or a peroxide initiator, via a radical chain mechanism[4](https://onlinelibrary.wiley.com/doi/10.1002/9780470638859.conrr680) |
| Why it is selective | It maintains a very low steady-state concentration of Br2, which favors substitution over electrophilic addition to the double bond[5](https://ggckondagaon.in/Content/157_105_Book_AdvancedOrganicChemistry_Carey-Sundberg2007.pdf) |
| Other uses | Bromohydrin formation from alkenes in aqueous DMSO; electrophilic bromination of activated aromatics, often with an acid or metal catalyst[6](https://ncstate.pressbooks.pub/ncstateorgchem/chapter/halohydrins-from-alkenes-addition-of-ho-x/) • [7](https://www.sciencedirect.com/science/article/pii/S004040201731013X) |
| Handling | Classified as an oxidizing solid (GHS category 3) and corrosive to metals; very toxic to aquatic life[8](https://www.sigmaaldrich.com/US/en/sds/aldrich/b81255) |
## Structure and physical properties
NBS is the N-brominated derivative of succinimide, the cyclic imide of succinic acid. PubChem describes it as a five-membered cyclic dicarboximide compound having a bromo substituent on the nitrogen atom, functionally related to succinimide.[1](https://pubchem.ncbi.nlm.nih.gov/compound/N-Bromosuccinimide) It is a convenient, inexpensive, and widely available crystalline compound.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC13385683/) Supplier data list a melting point of 176 °C with decomposition,[3](https://www.tcichemicals.com/US/en/p/B0656) although a 2026 review gives 153 °C.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC13385683/)
Unlike bromine itself, a corrosive and fuming brown liquid, NBS is an easily handled crystalline solid, which is a major practical reason for its use.[9](https://www.cur.ac.rw/mis/main/library/documents/book_file/digital-66644eea87c353.30190490.pdf) It can be purified by recrystallization from hot water: [Organic Syntheses](https://www.edgepedia.org/organic-syntheses) procedures dissolve it in water at about 90 °C and cool the orange solution to give colorless plates.[10](https://www.orgsyn.org/demo.aspx?prep=v101p0207) Purity matters in practice; less pure NBS leads to greater contamination with mono-brominated byproducts in sensitive procedures.[10](https://www.orgsyn.org/demo.aspx?prep=v101p0207)
## Allylic and benzylic bromination
The reaction for which NBS is best known is the Wohl–Ziegler bromination, the bromination of unsaturated organic compounds at the allylic or benzylic position (or the α-position of an aromatic side chain) using NBS as the reagent.[4](https://onlinelibrary.wiley.com/doi/10.1002/9780470638859.conrr680) In a typical example, cyclohexene treated with NBS, light, and carbon tetrachloride gives 3-bromocyclohexene in 85% yield, with succinimide as the coproduct.[11](https://openstax.org/books/organic-chemistry/pages/10-3-preparing-alkyl-halides-from-alkenes-allylic-bromination)
The reaction proceeds by a radical chain pathway. A bromine radical abstracts an allylic hydrogen atom, forming a resonance-stabilized allylic radical plus HBr; the HBr then reacts with NBS to generate Br2, which in turn reacts with the allylic radical to yield the brominated product and a bromine radical that continues the chain.[11](https://openstax.org/books/organic-chemistry/pages/10-3-preparing-alkyl-halides-from-alkenes-allylic-bromination) The selectivity for the allylic site is explained by bond dissociation energies. Breaking a C−H bond at a typical secondary alkyl carbon requires roughly 410 kJ/mol (98 kcal/mol), and at a vinylic position roughly 465 kJ/mol (111 kcal/mol), whereas an allylic C−H bond needs only about 370 kJ/mol (88 kcal/mol); the resulting allylic radical is therefore about 40 kJ/mol (9 kcal/mol) more stable than an ordinary alkyl radical.[11](https://openstax.org/books/organic-chemistry/pages/10-3-preparing-alkyl-halides-from-alkenes-allylic-bromination)
**The role of low bromine concentration.** Allylic bromination must compete with polar addition of bromine across the double bond through a bromonium ion (bridged three-membered cation formed when bromine adds across a double bond). The two pathways differ in their dependence on bromine concentration: the [radical substitution](https://www.edgepedia.org/radical-substitution) is half order in Br2, whereas the addition is first or second order, so keeping the Br2 concentration very low favors substitution over addition.[5](https://ggckondagaon.in/Content/157_105_Book_AdvancedOrganicChemistry_Carey-Sundberg2007.pdf) NBS accomplishes this by regenerating Br2 from the HBr produced in each chain step, supplying bromine only as it is consumed.[11](https://openstax.org/books/organic-chemistry/pages/10-3-preparing-alkyl-halides-from-alkenes-allylic-bromination)
**Which radical carries the chain.** Early mechanistic work established the radical-chain character of the reaction, and a 1948 Chemical Reviews review by [Carl Djerassi](https://www.edgepedia.org/carl-djerassi) collected the Wohl–Ziegler literature to that date.[12](https://pubmed.ncbi.nlm.nih.gov/18887958/) Competitive allylic bromination studies by J. H. Incremona and James C. Martin, a physical organic chemist at the University of Illinois, found near-identical selectivities for molecular bromine, NBS, and N-bromotetramethylsuccinimide, providing strong evidence that the free bromine radical, not a succinimidyl radical, is the chain-carrying species, with NBS serving to maintain a low steady-state concentration of Br2.[13](https://www.chemsrc.com/en/Paper/14981.html) Stereochemical evidence points the same way: Dauben and McCoy showed in 1959 that (−)-α-deuterio-ethylbenzene brominated with NBS in refluxing carbon tetrachloride gave phenylmethylcarbinyl bromide with at least 99.7% racemization, consistent with a completely free benzylic radical intermediate that racemizes at least 600 times faster than it reacts with the brominating species.[14](https://hero.epa.gov/reference/11547683/)
The Wohl–Ziegler reaction has limits: it has been reported not to work for conjugated olefins and 1,4-dienes, which act as inhibitors of the bromination.[4](https://onlinelibrary.wiley.com/doi/10.1002/9780470638859.conrr680)
## Electrophilic bromination reactions
NBS is also a source of electrophilic bromine (Br+). In water or aqueous DMSO it decomposes to Br2, which adds to alkenes through a bromonium ion; when water is the nucleophile that opens the bromonium ion, the product is a bromohydrin, a 1,2-halo alcohol, formed with anti addition. Because few alkenes are soluble in water, bromohydrin formation is often carried out in aqueous dimethyl sulfoxide with NBS as the bromine source.[6](https://ncstate.pressbooks.pub/ncstateorgchem/chapter/halohydrins-from-alkenes-addition-of-ho-x/)
NBS also brominates aromatic rings. Activated aromatics such as phenols and anilines react readily, while less activated substrates such as alkylbenzenes and deactivated aromatics require activation with a Brønsted or Lewis acid catalyst.[7](https://www.sciencedirect.com/science/article/pii/S004040201731013X) Kinetic studies of anilides, anisoles, and phenols in 80% aqueous acetic acid found the reaction first order in the aromatic substrate and zero order in NBS, consistent with attack by Br+ or a solvated Br+ ion on the aromatic ring.[15](https://onlinelibrary.wiley.com/doi/pdf/10.1002/kin.550121103) Catalytic methods extend the scope: an AuCl3-catalyzed bromination of aromatic rings with NBS works with catalyst loadings down to 0.01 mol% and can be combined with transition-metal-catalyzed transformations.[16](https://onlinelibrary.wiley.com/doi/10.1002/anie.200906699)
## Wider reactivity and history
Beyond bromination, NBS participates in rearrangements, hydrolysis, multicomponent reactions, C−C bond cleavage of β-keto amides, oxidation, catalysis, aromatization, and one-pot tandem reactions, roles compiled in a 2026 review titled "Redefining N-Bromosuccinimide: Chemistry Beyond Allylic Bromination."[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC13385683/) In one radical application, a bromine radical forms a hypobromite intermediate with the hydroxyl group of cyclobutanols, driving a ring expansion by a free radical mechanism.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC13385683/)
The reagent's history traces to the N-bromoamides introduced in the early twentieth century. Wohl reported bromination with N-bromoacetamide in 1919 (the Wohl reaction), and Ziegler and coworkers introduced NBS for allylic bromination in the late 1930s, with their full account in 1942; bromination by NBS became known as the Wohl–Ziegler reaction.[4](https://onlinelibrary.wiley.com/doi/10.1002/9780470638859.conrr680) • [2](https://pmc.ncbi.nlm.nih.gov/articles/PMC13385683/) NBS is typically prepared by the reaction of succinimide with bromine in alkaline ice-water medium.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC13385683/)
## Safety
NBS is classified as an oxidizing solid (GHS category 3) and is corrosive to metals; it causes skin and serious eye irritation and may cause an allergic skin reaction.[8](https://www.sigmaaldrich.com/US/en/sds/aldrich/b81255) It is very toxic to aquatic life, with a 48-hour EC50 of 0.65 mg/L against *Daphnia magna*, and is readily biodegradable (98% in 35 days in an activated-sludge test).[8](https://www.sigmaaldrich.com/US/en/sds/aldrich/b81255) Reagent-grade material is typically sold at 99% purity and recrystallized before use in demanding procedures.[10](https://www.orgsyn.org/demo.aspx?prep=v101p0207)
## References
1. [N-bromobutanimide (N-Bromosuccinimide), CID 67184, PubChem, National Library of Medicine](https://pubchem.ncbi.nlm.nih.gov/compound/N-Bromosuccinimide)
2. [Redefining N-Bromosuccinimide: Chemistry Beyond Allylic Bromination, Chemistry – An Asian Journal (2026), PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC13385683/)
3. [N-Bromosuccinimide, CAS 128-08-5, TCI America product page](https://www.tcichemicals.com/US/en/p/B0656)
4. [Wohl–Ziegler Bromination, Name Reactions and Reagents in Organic Synthesis (Wiley, 2010)](https://onlinelibrary.wiley.com/doi/10.1002/9780470638859.conrr680)
5. [Advanced Organic Chemistry (Carey & Sundberg), excerpt on allylic bromination kinetics](https://ggckondagaon.in/Content/157_105_Book_AdvancedOrganicChemistry_Carey-Sundberg2007.pdf)
6. [Halohydrins from Alkenes: Addition of HO–X, Organic Chemistry (OpenStax adaptation), NC State](https://ncstate.pressbooks.pub/ncstateorgchem/chapter/halohydrins-from-alkenes-addition-of-ho-x/)
7. [Regioselective monobromination of aromatics via a halogen bond acceptor-donor interaction of catalytic thioamide and N-bromosuccinimide, Tetrahedron Letters (2017)](https://www.sciencedirect.com/science/article/pii/S004040201731013X)
8. [Safety Data Sheet, N-Bromosuccinimide (Aldrich B81255), MilliporeSigma](https://www.sigmaaldrich.com/US/en/sds/aldrich/b81255)
9. [Organic Chemistry (textbook excerpt on NBS as an easily handled crystalline solid)](https://www.cur.ac.rw/mis/main/library/documents/book_file/digital-66644eea87c353.30190490.pdf)
10. [Organic Syntheses, Vol. 101, p. 207 (NBS recrystallization procedure and purity notes)](https://www.orgsyn.org/demo.aspx?prep=v101p0207)
11. [Preparing Alkyl Halides from Alkenes: Allylic Bromination, Organic Chemistry, OpenStax (McMurry)](https://openstax.org/books/organic-chemistry/pages/10-3-preparing-alkyl-halides-from-alkenes-allylic-bromination)
12. [C. Djerassi (1948). Brominations with N-bromosuccinimide and related compounds; the Wohl-Ziegler reaction. Chemical Reviews 43(2): 271–317, PubMed](https://pubmed.ncbi.nlm.nih.gov/18887958/)
13. [J. H. Incremona and J. C. Martin (1970). N-Bromosuccinimide. Mechanisms of allylic bromination and related reactions. JACS 92(3): 627–634, abstract via Chemsrc](https://www.chemsrc.com/en/Paper/14981.html)
14. [Dauben, H. J. and McCoy, L. L. (1959). N-Bromosuccinimide. III. Stereochemical Course of Benzylic Bromination. JACS 81(20): 5404–5409, EPA HERO record](https://hero.epa.gov/reference/11547683/)
15. [S. Sivakamasundari and R. Ganesan (1980). Kinetics and mechanism of the bromination of aromatic compounds by N-bromosuccinimide in solution. Int. J. Chem. Kinet. 12: 837–850](https://onlinelibrary.wiley.com/doi/pdf/10.1002/kin.550121103)
16. [Mo, F. and colleagues (2010). Gold-Catalyzed Halogenation of Aromatics by N-Halosuccinimides. Angewandte Chemie International Edition](https://onlinelibrary.wiley.com/doi/10.1002/anie.200906699)
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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Organic substances › Organic reactions, structure and reference › Organic reactions and synthetic methods › Functional group interconversion, oxidation, and reduction › Halogenation and haloalkane preparation*
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