What N-Iodosuccinimide Is
N-Iodosuccinimide, abbreviated NIS, is a white to off-white crystalline powder formed by the iodination of succinimide. Its molecular formula is C4H4INO2 and its molecular weight is 224.98 g/mol. The compound carries a very weak nitrogen-iodine bond, which is the key to its reactivity: the iodine is delivered readily to electron-rich substrates while the succinimide moiety leaves as a stable, innocuous by-product.
NIS is described as a mild and selective iodinating agent because it introduces iodine under relatively gentle conditions and can be directed to specific positions on a molecule. It dissolves in common organic solvents such as dichloromethane, acetonitrile, dimethylformamide and acetone, which allows reactions to be run at low temperature in solution.
Typical Specification
| Parameter | Typical value |
|---|---|
| CAS number | 516-12-1 |
| Molecular formula | C4H4INO2 |
| Molecular weight | 224.98 g/mol |
| Appearance | White to off-white crystalline powder |
| Assay (by iodometric titration) | 98% minimum |
| Active iodine content | Not less than 55% |
| Melting range | 200-203 °C with decomposition |
| Water content | 0.5% maximum |
| Solubility | Soluble in dichloromethane, acetonitrile, DMF and acetone |
| Packaging | 25 kg fibre drum with inner polyethylene liner; 1 kg and 5 kg foil-lined packs |
Organic Synthesis Applications
In organic synthesis NIS is used for iodination reactions across a very wide range of substrates. It adds iodine efficiently to aromatic rings, alkenes and heterocycles, and it also promotes related transformations such as iodoetherification, iodolactonisation and electrophilic cyclisation.
Aromatic iodination: electron-rich arenes react smoothly to give aryl iodides, which are among the most useful coupling partners in modern cross-coupling chemistry.
Alkene and alkyne functionalisation: addition across carbon-carbon double bonds gives vicinal iodo derivatives that can be converted into amines, ethers or halides.
Pharmaceutical intermediates: in the preparation of iodinated drug substances, NIS places iodine precisely at the required position of the molecular framework, which changes the properties and biological activity of the target compound.
Process advantages: compared with some traditional iodination routes, NIS-mediated reactions are easier to control, use milder conditions and reduce hazardous by-product formation.
Biochemical and Labelling Applications
In biochemistry, NIS is used to modify biomolecules. It can iodinate proteins, peptides and other substrates, which is useful for a range of research purposes.
Tracers and probes: iodinated biomolecules serve as tracers in studies of protein-protein interactions, protein folding and cellular uptake.
Selective labelling: NIS reacts with certain amino acid residues without causing significant denaturation, which makes it a preferred reagent where the native structure must be preserved.
Analytical standards: iodinated reference compounds are used to calibrate radio-labelled and mass-spectrometric assays.
Materials Science Applications
In materials science NIS is used to functionalise surfaces and polymer backbones. Introducing iodine-containing groups onto polymers or nanoparticles changes their reactivity and their physical behaviour.
Surface functionalisation: iodine groups grafted onto polymer or nanoparticle surfaces act as anchors for further chemistry and as heavy-atom tags.
Property modification: the modified materials can show enhanced conductivity, altered optical characteristics or improved compatibility with other substances.
Advanced materials: these handles support the development of materials for electronics, optics and catalysis, where post-functionalisation is often the only practical route to the required structure.
Handling, Stability and Storage
NIS is a reactive solid that must be kept dry and cool. It is sensitive to moisture and light, and it can decompose on prolonged exposure to heat, releasing iodine.
Store in a tightly closed container in a cool, dark, dry place, away from heat sources, strong reducing agents and combustible materials.
Weigh and transfer in a fume hood or ventilated enclosure and use gloves, safety goggles and a lab coat; iodine-containing dust causes irritation.
Do not mix with strong oxidisers or with amines in bulk, and keep the material away from metal powders.
Working solutions in dichloromethane or acetonitrile are best prepared freshly and used within the day, since they slowly liberate iodine on standing.
Frequently Asked Questions
Q: What is N-iodosuccinimide used for?
A: It is used as a mild, selective iodinating agent in organic synthesis, in the iodination and labelling of biomolecules, and in the surface functionalisation of polymers and nanoparticles.
Q: Is NIS soluble in water?
A: It is not intended for aqueous systems; it is soluble in dichloromethane, acetonitrile, dimethylformamide and acetone, and it hydrolyses slowly in the presence of water.
Q: How is the assay determined?
A: The active iodine content is normally released by iodometric titration against standard sodium thiosulfate solution, which gives both assay and iodine content.
Q: How should NIS be stored?
A: Keep it cool, dry and protected from light in a tightly closed container, away from heat, reducing agents and metal powders.
Q: Can NIS be used for iodolactonisation?
A: Yes. In addition to simple iodination, NIS mediates electrophilic cyclisations including iodolactonisation and iodoetherification of unsaturated acids and alcohols.
Q: What is the difference between NIS and elemental iodine?
A: NIS delivers iodine in a controlled, mildly electrophilic form with a stable succinimide by-product, so it is easier to handle, less corrosive to equipment and more selective than elemental iodine in many reactions.