Potassium Sulfite (10117-38-1) Physical and Chemical Properties
Potassium Sulfite
Inorganic sulfite salt commonly used as a reducing agent, antioxidant and preservative in industrial formulations, food processing, photography and cosmetic manufacturing.
| CAS Number | 10117-38-1 |
| Family | Sulfites (inorganic salt) |
| Typical Form | White crystalline powder or solid (commonly dihydrate) |
| Common Grades | EP, FCC |
Potassium sulfite is an inorganic salt of the sulfite anion and the potassium cation; it is commonly encountered as the dipotassium salt of sulfurous acid. Structurally it is an ionic compound composed of two potassium ions and one sulfite anion, formally represented by the empirical formula K2O3S (commonly written as K2SO3). The sulfite anion features a trigonal‑pyramidal or distorted trigonal planar \(SO_3^{2-}\) geometry with localized lone pairs on sulfur-derived oxygens; the overall electronic structure imparts strong ionic character, considerable polarity, and a high topological polar surface area for the molecular unit.
In aqueous media potassium sulfite behaves as a source of \(SO_3^{2-}\) (sulfite) which is the conjugate base of sulfurous acid. Aqueous solutions are typically basic to near‑neutral depending on concentration and partial protonation (formation of bisulfite \(HSO_3^{-}\)); contact with acids converts sulfite species to sulfur dioxide with concomitant acidification and gas evolution. Sulfites are reducing agents in many chemical contexts and are progressively oxidized in air to the corresponding sulfate anion over time; thermal decomposition is observed for solid hydrates on heating.
Industrial relevance is broad: potassium sulfite is used as a preservative/antioxidant in food and cosmetics, as a component of photographic developers, and in chemical manufacturing where mild reducing properties are required. It is also documented in certain pharmaceutical formulations historically used for specific actions (e.g., cathartic/diuretic in older uses). Common commercial grades reported for this substance include: EP, FCC.
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 melting point value for this property is available in the current data context; available experimental notes indicate the material (dihydrate) decomposes on heating.
Solubility in Water
Dipotassium sulfite (dihydrate) is water‑soluble. Experimental descriptions report the dihydrate dissolves in about 3.5 parts water (i.e., roughly 1 mass part solute per 3.5 parts solvent in the referenced description). The dihydrate form is reported as white crystals or crystalline powder; it is insoluble in ammonia and only slightly soluble in alcohol.
Solution pH (Qualitative Behavior)
Aqueous solutions of the dihydrate are mildly basic; reported solution pH for the dihydrate is about \(\mathrm{pH}\) 8. In practice the solution pH will depend on concentration and the extent of partial protonation to \(HSO_3^{-}\), and will shift acidic upon addition of mineral acids with evolution of \(SO_2\).
Chemical Properties
Acid–Base Behavior
Potassium sulfite supplies the sulfite anion \(SO_3^{2-}\) in solution, which is the conjugate base of sulfurous acid. In water the anion can be partially protonated to bisulfite \(HSO_3^{-}\); conversely, addition of acids converts sulfite/bisulfite into dissolved sulfur dioxide and ultimately to sulfurous acid in the aqueous phase, with gas release when acidification is sufficient. No numerical \(pK_a\) values for these equilibria are provided in the current data context.
As a salt of a weak acid, solid potassium sulfite in concentrated solution normally produces neutral to basic pH values and will react with strong acids to liberate \(SO_2\).
Reactivity and Stability
Potassium sulfite is classed as a reducing agent and is subject to oxidative conversion to the corresponding sulfate on exposure to air; experimental notes state the dihydrate gradually oxidizes in air to sulfate. The dihydrate form decomposes upon heating. Contact with acids or oxidizing agents can lead to evolution of sulfur dioxide and other decomposition events. Storage recommendations for the dihydrate are to keep the material well closed and in a cool place to limit hydrolysis/oxidation. Susceptibility to oxidation and acid‑driven decomposition are the principal stability considerations for handling and storage.
Molecular and Ionic Parameters
Formula and Molecular Weight
- Molecular formula: K2O3S (often written as K2SO3)
- Molecular weight: 158.26
- Exact mass / Monoisotopic mass: 157.88422800
Constituent Ions
The compound dissociates into potassium cations and the sulfite anion in solution: - Potassium ion: \( \mathrm{K}^{+} \) - Sulfite ion: \( \mathrm{SO}_3^{2-} \)
Hydration (dihydrate) affects physical form and solubility behavior; the active dissolved species in aqueous solution are the ions above and their protonation equilibria.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS number: 10117-38-1
- Deprecated CAS: 126048-06-4
- European Community (EC) number: 233-321-1
- UNII: 015KZC652E
- DSSTox Substance ID: DTXSID80889532
- HMDB ID: HMDB0303527
- InChI: InChI=1S/2K.H2O3S/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2
- InChIKey: BHZRJJOHZFYXTO-UHFFFAOYSA-L
- SMILES: [O-]S(=O)[O-].[K+].[K+]
Synonyms and Common Names
Depositor‑supplied synonyms and alternative names include (selection from supplied list): POTASSIUM SULFITE, Dipotassium sulfite, Potassium sulphite, Sulfurous acid, dipotassium salt, Potassium sulfite (K2SO3), Sulfurous acid, potassium salt, Sulfurous acid, potassium salt (1:2), Potassium sulfite(IV), E225, K2O3S, and related vendor/registry labels such as UNII‑015KZC652E, DTXSID80889532, EC 233-321-1. Additional commercial descriptors and grade‑annotated names appear among supplier listings (e.g., "Potassium sulfite, 90%", "Potassium sulfite, SAJ first grade, >=95.0%").
Industrial and Commercial Applications
Functional Roles and Use Sectors
Potassium sulfite is used as an antioxidant and preservative in certain food and cosmetic formulations and as a reducing agent in photographic processing. It is applied where mild reducing conditions or sulfite‑based preservation is required. The material is also listed in contexts of chemical intermediates, photosensitive chemicals for photography, and in some agricultural/soil amendment roles where sulfite or sulfurous species are utilized.
Formulations/grades reported in manufacturing and supply contexts include technical, CP (chemically pure), and FCC grades; common commercial grade labels reported for this substance include EP and FCC.
Typical Application Examples
- Photographic developers and related photosensitive chemical processes — acts as a preservative/reducing component in developer solutions.
- Food industry — used as a preservative/antioxidant in specific applications (listed as a substance added to food; regulatory document reference: 21 CFR 73.85 as the listed document number in that context).
- Cosmetic formulations — employed as a preservative and reducing agent in some hair and cosmetic preparations.
- Chemical manufacturing — as a mild reducing agent in synthetic or processing operations where sulfite chemistry is appropriate.
- Historical/older pharmaceutical uses — documented uses include cathartic and diuretic actions in legacy references (modern medicinal use is not a standard application).
If a concise application summary is required beyond the above, selection should be guided by the functional properties described earlier (reducing ability, preservative/antioxidant action, aqueous ionic behavior).
Safety and Handling Overview
Health and Environmental Hazards
Potassium sulfite is an irritant: skin and eye contact may cause irritation, and inhalation of dust or aerosols may cause respiratory tract irritation. Sulfite salts can provoke bronchoconstriction in sulfite‑sensitive asthmatic individuals; populations with sulfite sensitivity are at higher risk from low concentrations in food or air. Reported acute toxicity descriptors for sulfite salts indicate moderate toxicity at high doses; representative historical values cite a probable oral lethal dose range for humans of approximately \(0.5!-!5\,\mathrm{g}\,\mathrm{kg}^{-1}\) for sulfite salts as a class under severe exposure scenarios. A JECFA group acceptable daily intake (expressed as sulfur dioxide equivalent for sulfite species) is reported as \(0!-!0.7\,\mathrm{mg}\,\mathrm{kg}^{-1}\) body weight.
Reported hazard classifications include skin and eye irritation potentials and possible respiratory irritation or acute toxicity depending on formulation and impurity profile. In contact with acids the substance may liberate sulfur dioxide gas, which is irritating and hazardous at sufficient concentrations.
For emergency treatment of significant exposure follow supportive care principles: ensure patent airway, administer oxygen if respiratory distress, irrigate contaminated eyes with copious water or saline, and seek immediate medical care. Specific antidotes are not established; treatment is symptomatic and supportive.
For environmental management and disposal, follow applicable local regulations; avoid uncontrolled release to waterways because of chemical oxygen demand and potential aquatic impacts from sulfite/sulfate chemistry.
Storage and Handling Considerations
Store potassium sulfite in tightly closed containers in a cool, dry, well‑ventilated area protected from air and moisture to minimize oxidation to sulfate. For the dihydrate, recommendations include keeping the material well closed in a cool place. Avoid exposure to strong oxidizers and acids; control dust and use appropriate containment to prevent inhalation exposures.
Use standard industrial hygiene controls: gloves, eye protection, and respiratory protection as appropriate for airborne dusts or mists. For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
