Arsenite (15502-74-6) Physical and Chemical Properties
Arsenite
The trivalent arsenite anion (AsO3(3-)) is supplied as inorganic salts used as research reagents and analytical standards for R&D, QA/QC, and specialized synthesis workflows.
| CAS Number | 15502-74-6 |
| Family | Inorganic oxyanions |
| Typical Form | Powder or crystalline salt |
| Common Grades | EP |
Arsenite (the trivalent arsenic oxyanion formally described as arsenite(3-), formula AsO3-3) is an inorganic oxyanion derived from arsenous acid by removal of three protons. Structurally it is a small, highly polar trigonal arrangement around arsenic(III) with three oxo/oxy ligands; the species carries a formal charge of \(-3\) and functions as a hard, anionic ligand in coordination chemistry. Electronically, arsenic in this oxidation state has a lone pair that can influence stereochemistry in covalent molecular species but in the fully deprotonated ionic AsO3-3 the dominant interactions are ionic and coordinate bonding with cations and metal centers.
As a wholly charged oxyanion, arsenite is highly hydrophilic and typically exists in aqueous systems as a dissolved anion or as salts with alkali/alkaline earth or transition metal counterions. Acid–base equilibria of the arsenous acid/arsenite system control speciation: protonated forms (arsenous acid and partially deprotonated anions) predominate at lower pH, while fully deprotonated arsenite(3-) is favored at strongly basic conditions. Chemically, arsenite(III) species are redox-active relative to arsenate(As(V)), readily forming complexes with thiol-containing biomolecules and coordinating to soft metal centers; these behaviors underlie its biochemical toxicity and environmental mobility.
Arsenite is widely encountered in environmental chemistry and toxicology contexts (water contamination, geochemical mobility) and in biochemical research as a probe of arsenic metabolism and enzyme inhibition mechanisms. It is also encountered as a defined ionic species in analytical and preparative chemistry. Common commercial grades reported for this substance include: EP.
Basic Physical Properties
Density
No experimentally established value for this property is available in the current data context.
Melting or Decomposition Point
No experimentally established value for this property is available in the current data context.
Solubility in Water
As a multiply charged oxyanion, arsenite is expected to be highly soluble in water as free anion or as soluble salts with common cations (e.g., Na+, K+). In aqueous systems it will exist primarily in dissolved ionic form and may form insoluble metal arsenites under conditions where sparingly soluble metal cations (e.g., Pb2+, Ag+) are present.
Solution pH (Qualitative Behavior)
No individual numeric \(\mathrm{p}K_a\) values are provided in the current data context. Qualitatively, speciation is pH-dependent: under acidic conditions the arsenous acid/protonated species predominate, while progressive deprotonation occurs with increasing pH, leading to the fully deprotonated arsenite(3-) anion at sufficiently high pH. Thus solution pH controls the distribution between neutral/partially protonated forms and the \(-3\) charged oxyanion.
Chemical Properties
Acid–Base Behavior
Arsenite(3-) is the conjugate base of arsenous acid; the formal charge of the anion is \(-3\) (formal charge: \(-3\) as reported). In aqueous chemistry the species participates in stepwise protonation/deprotonation equilibria typical of polyprotic oxyacids, and total speciation depends on solution pH and concentration. As an anion, arsenite acts as a Lewis base toward metal cations and can coordinate in monodentate or bridging modes depending on the metal center.
Reactivity and Stability
Arsenite (As(III)) is chemically distinguishable from arsenate (As(V)) by its redox chemistry: arsenite is more readily oxidized to arsenate under oxidizing conditions and can act as a reducing agent in some contexts. It forms stable complexes with thiol-containing ligands (cysteine residues, glutathione), which underpins much of its biochemical reactivity and toxicity. In environmental and synthetic systems arsenite forms coordination compounds and can precipitate as metal arsenites with suitable countercations. Hydrolytic stability in aqueous solution is high for the ionic form (dissolved oxyanion), but redox, complexation and precipitation reactions control persistence and mobility. Note: three-dimensional conformer generation was not performed here because of limitations for force-field parametrization for arsenic-containing species (conformer generation disallowed since MMFF94s unsupported element).
Molecular and Ionic Parameters
Formula and Molecular Weight
- Molecular formula: AsO3-3
- Molecular weight: \(122.920\,\mathrm{g}\,\mathrm{mol}^{-1}\)
- Exact mass: \(122.906338\,\mathrm{Da}\)
- Monoisotopic mass: \(122.906338\,\mathrm{Da}\)
Constituent Ions
- Constituent anion: arsenite(3-) (AsO3-3), formal charge \(-3\).
- Salt formation: exists as salts of arsenous acid with countercations (e.g., Na+, K+, metal cations) in practical materials and reagents.
- Hydrogen-bonding and topological parameters (computed descriptors): hydrogen bond donor count \(0\); hydrogen bond acceptor count \(3\); topological polar surface area \(69.2\); rotatable bond count \(0\); heavy atom count \(4\); complexity \(8\).
Structural identifiers (structural descriptors provided in computational annotations): SMILES string "[O-]As[O-]" and InChI "InChI=1S/AsO3/c2-1(3)4/q-3".
Identifiers and Synonyms
Registry Numbers and Codes
- CAS number: 15502-74-6
- UNII: N5509X556J
- ChEBI: CHEBI:29866
- DrugBank: DB18509
- DSSTox Substance ID: DTXSID0074007
- KEGG: C06697
- Nikkaji Number: J2.763.523G
- Wikidata: Q26841209
- InChIKey: OWTFKEBRIAXSMO-UHFFFAOYSA-N
- SMILES: [O-]As[O-]
Synonyms and Common Names
Reported synonyms and common names include (as supplied): arsenite; Arsenite ion; arsenite ions; ARSENITE ANION; ortho-arsenite; arsorite; Trisoxylatoarsine; arsenite(3-); ortho-arsenite ion; AsO3(3-); AsO3. These names are used in chemical nomenclature, biochemical contexts and vendor/depositor listings.
Industrial and Commercial Applications
Functional Roles and Use Sectors
Arsenite species serve as key reference analytes and model oxyanions in environmental chemistry, geochemistry and analytical chemistry where arsenic speciation is important. In biochemical and toxicological research arsenite is employed to study arsenic metabolism, mechanisms of enzyme inhibition (notably via thiol interaction), and cellular responses to metalloid stress. In industrial contexts, arsenite species appear as contaminants or intermediates in metallurgical and water-treatment situations rather than as bulk commercial products.
Typical Application Examples
- Analytical standards and calibration species for arsenic speciation studies in environmental monitoring and water quality analysis.
- Reagents or model ligands in laboratory studies of coordination chemistry and metal–ligand interactions.
- Research reagent in toxicology and microbiology; arsenite has been identified as a metabolite in certain microbial strains (for example, Escherichia coli strain annotations indicate occurrence in metabolic contexts).
If process- or product-specific application details are needed for procurement or formulation, consult product literature from suppliers and application notes specific to the intended use.
Reported commercial grades: EP.
Safety and Handling Overview
Health and Environmental Hazards
Arsenite (As(III)) is a biologically active, high-concern toxicant. Classification annotations indicate potential teratogenic activity and possible endocrine-disrupting effects. Mechanistically, arsenite species bind to protein thiol groups and disrupt enzymatic function and cellular redox homeostasis; these interactions are central to acute and chronic toxicity. Environmentally, the arsenite oxyanion is mobile in aqueous media and can contribute to contamination of groundwater and surface waters; redox conversion to arsenate and complexation/precipitation reactions influence environmental fate. Exposure routes of primary concern are ingestion and inhalation of dust or aerosols and dermal contact with concentrated solutions or solids.
For detailed, product-specific hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
Storage and Handling Considerations
Handle arsenite-containing materials using standard industrial hygiene controls for toxic inorganic compounds: use appropriate personal protective equipment (gloves, eye protection, lab coat or protective clothing, and respiratory protection where aerosol generation or poor ventilation exists), work in a fume hood for solutions or dusts, and implement measures to prevent accidental release to the environment. Store in clearly labeled, corrosion-resistant containers; segregate from incompatible materials (strong oxidizers, strong acids or bases where undesired reactions or conversion to other arsenic species could occur). Manage waste and decontamination solutions as hazardous waste consistent with local regulations. For emergency response and spill remediation follow institutional procedures and consult the applicable SDS.
