Nitronium (10102-44-0) Physical and Chemical Properties
Nitronium
A strong electrophilic NO2+ species typically supplied as stabilized salts for use in controlled nitration and process chemistry applications.
| CAS Number | 10102-44-0 |
| Family | Nitronium (NO2+) ion |
| Typical Form | Stabilized as crystalline salts or in solution |
| Common Grades | EP |
Nitronium is a small, inorganic oxocation of the nitrogen–oxygen class; structurally it is the dioxido nitrogen cation with formula \(\mathrm{NO}_2^{+}\). The ion is formally isoelectronic with carbon dioxide and adopts a linear O–N–O geometry with two equivalent N=O bonds and a formal charge localized on the nitrogen–oxygen framework. Electronic structure is dominated by strong π-bonding between nitrogen and oxygen and by the high electrophilicity of the nitrogen center; the two oxygen atoms provide lone-pair acceptance sites but the overall species is a one-plus cation with no hydrogen-bond donors.
Because it is a charged, non-neutral species, nitronium is highly polar and is typically encountered as stabilized salts or as solvated ions in strongly acidic media rather than as a free neutral species. It is a powerful electrophile and strong Lewis acid: it readily effects electrophilic aromatic substitution (nitration) and reacts with nucleophiles, water and basic substrates. Hydrolysis and solvation in protic media lead to rapid conversion to nitrogen oxides and oxyacids; conversely, nitronium is generated in situ under dehydrating, strongly acidic conditions (e.g., mixed acid systems) or isolated as salts with non-nucleophilic counterions for use as nitrating reagents.
Common commercial grades reported for this substance include: EP.
Molecular Parameters
Molecular Weight and Formula
- Molecular formula: \(\mathrm{NO}_2^{+}\) (reported as NO2+).
- Molecular weight: 46.006 \(\mathrm{g}\,\mathrm{mol}^{-1}\).
- Exact mass / monoisotopic mass: 45.992903243 (atomic mass units).
The small molecular weight and compact triatomic structure are consistent with a high charge density; this contributes to strong solvation, low intrinsic lipophilicity, and high mobility in ionic lattices or superacidic solutions.
Charge State and Ion Type
- Formal charge: \(+1\).
- Ion type: simple oxocation (dioxonitrogen(1+)).
Nitronium is a closed-shell cation rather than a radical; it behaves as a classical electrophile/Lewis acid. In condensed phases it is normally present as a counterion pair (salts) or as a strongly solvated ion in acidic media.
LogP and Polarity
No experimentally established value for this property is available in the current data context.
Qualitatively, nitronium is extremely polar owing to its formal positive charge and small size. As an ion it has negligible intrinsic partitioning into nonpolar phases; lipophilicity in practice is governed by the counterion and solvation environment (for example, in organic media nitronium can be transferred as ion pairs with large, poorly coordinating anions).
Structural Identifiers (SMILES, InChI)
- SMILES: N+=O
- InChI: InChI=1S/NO2/c2-1-3/q+1
- InChIKey: OMBRFUXPXNIUCZ-UHFFFAOYSA-N
The canonical SMILES and InChI represent the linear dioxo cation; these identifiers are suitable for structure-based searches and unambiguous machine representation of the ion.
Acid–Base Behavior
Conjugate Acid and Speciation
As a cationic species, nitronium does not have a conventional deprotonation pKa; rather, its acid–base behavior is described by its Lewis acidity and by equilibria that interconvert it with other nitrogen–oxygen species. In protic or basic media nitronium is rapidly quenched by nucleophiles (including water), converting to nitric acid or other nitrogen oxides. In strongly acidic, dehydrating environments (for example, mixtures that remove water from nitric acid) nitronium is generated and can exist transiently as a free electrophile or as a salt paired with non-nucleophilic anions.
Speciation in solution is therefore highly dependent on solvent polarity, water activity, and the nature of the counterion or medium; isolated crystalline salts with non-coordinating anions provide the most stable condensed-phase forms.
Acid–Base Equilibria and Qualitative pKa Discussion
No experimentally established value for this property is available in the current data context.
Qualitatively, nitronium functions as a strong electrophilic species rather than as a Bronsted acid or base in the usual sense. Its formation from nitric acid involves protonation/dehydration pathways under strongly acidic conditions; conversely, proton transfer and hydrolytic reactions rapidly remove nitronium in the presence of protic nucleophiles.
Chemical Reactivity
Chemical Stability
Nitronium is inherently reactive and typically unstable toward nucleophiles and moisture. It is a potent electrophile that readily nitrates activated aromatic systems and other nucleophilic substrates. Stability increases when the cation is paired with weakly coordinating, non-nucleophilic anions (e.g., certain fluorinated anions) and in aprotic, anhydrous, and low-nucleophilicity media or solid salts.
Thermal and oxidative stability of nitronium salts depends strongly on the counterion and crystal lattice; some salts are isolable and crystalline, while the free ion in solution is short-lived unless the environment is strongly dehydrating and acidic.
Formation and Hydrolysis Pathways
Formation: - Common laboratory generation: dehydration/protonation chemistry in mixed-acid systems (e.g., concentrated nitric acid in presence of a dehydrating strong acid) produces nitronium as the active electrophile for nitration reactions. - Chemical isolation: formation of crystalline nitronium salts with non-coordinating anions yields isolable sources of the cation for preparative use.
Hydrolysis / quench: - Nitronium reacts with water and other nucleophiles; a representative hydrolytic reaction is the conversion to nitric acid and a proton, e.g. \(\mathrm{NO}_2^{+} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{HNO}_3 + \mathrm{H}^{+}\). - Reaction with organic nucleophiles typically results in nitration or oxidative transformations depending on substrate and conditions.
These formation and destruction pathways underpin nitronium's role as the electrophile in industrial and laboratory nitration chemistry and explain the requirement for anhydrous, controlled conditions when handling the species or its salts.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS number: 10102-44-0
- ChEBI ID: CHEBI:29424
- Nikkaji Number: J2.460.898K
- Wikidata: Q418329
- InChIKey: OMBRFUXPXNIUCZ-UHFFFAOYSA-N
These registry entries and identifiers correspond to the nitronium ionic species and associated nomenclature records.
Synonyms and Structural Names
Common synonyms and alternative names reported include: - nitronium - dioxidonitrogen(1+) - nitronium ion - Nitryl cation - NO2+ - (NO2)(+) - Oxoazane oxide #
These synonyms reflect both systematic and trivial nomenclature for the \(\mathrm{NO}_2^{+}\) species.
Industrial and Commercial Applications
Role as Active Ingredient or Intermediate
Nitronium (as the active electrophile) is central to nitration chemistry: it is the reactive species that introduces nitro functional groups into aromatic and certain aliphatic substrates. In practice, nitronium is used or generated as an intermediate in the production of nitroaromatic intermediates for dyes, pharmaceuticals, agrochemicals and energetic materials. Isolable nitronium salts with non-coordinating anions are employed as convenient, storable nitrating reagents or electrophilic activators in synthetic chemistry.
Representative Application Contexts
- Electrophilic aromatic nitration in fine-chemical and process chemistry settings, typically generated in situ from acid mixtures or provided as a nitronium salt reagent.
- Preparation of nitro-functionalized intermediates for further synthetic elaboration (reduction, substitution, or other transformations).
- Research applications requiring a well-defined, strong electrophile or Lewis-acid catalyst in anhydrous, non-nucleophilic media.
If a concise application summary is not provided in a particular supply specification, selection of nitronium sources is normally based on the required reactivity, counterion influence, and compatibility with downstream process conditions.
Safety and Handling Overview
Toxicity and Biological Effects
Nitronium and its salts are corrosive and can cause severe chemical burns on contact with skin, eyes and mucous membranes. The ion and many of its salts are strong oxidizers and react exothermically with water and organic materials; inhalation of aerosols or mists is hazardous. Exposure controls should prioritize elimination of contact, effective ventilation, and use of appropriate personal protective equipment (chemical-resistant gloves, eye protection, face shield, protective clothing, and suitable respiratory protection when airborne concentrations cannot be excluded).
For quantitative toxicology endpoints (LD50, occupational exposure limits) consult product-specific safety documentation; such numerical values are not provided here.
Storage and Handling Considerations
- Store nitronium salts and nitronium-generating reagents under dry, inert atmosphere and in containers compatible with strong acids and oxidizers.
- Prevent contact with moisture, reducing agents, organic combustibles and incompatible materials; handle in fume hoods or enclosed systems designed for corrosive, oxidizing reagents.
- Use secondary containment and temperature control to avoid runaway hydrolysis or exothermic reactions.
- Dispose of wastes and neutralized residues following applicable local regulations and institutional procedures.
For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
