Sodium Thiosulfate
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Product Description
Sodium thiosulfate (Na₂S₂O₃) is a versatile, low-cost, and environmentally benign inorganic compound increasingly recognized for its multifaceted roles across energy, environmental, and biomedical fields. In energy-storage research it serves as a surface-functionalization agent that grafts sulfur-rich groups onto 2D materials such as boron-nitride and graphene oxide, generating conductive networks, suppressing restacking, and doubling specific capacitance in super-capacitor electrodes. When introduced during the chemical activation of carbonaceous wastes (e.g., bitumen coke, lignin, coconut shell), it acts as a pore moderator that preferentially generates ultramicropores (<0.8 nm), boosting CO₂ uptake by up to 21 % and raising CO₂/N₂ selectivity almost three-fold—critical metrics for next-generation carbon-capture sorbents. The same sulfur-donor ability is exploited in green organic synthesis, where catalytic Na₂S₂O₃·5H₂O triggers radical-mediated C–H sulfenylation, enabling one-pot, metal-free assembly of pharmaceutically relevant C-4-sulfenylated pyrazoles in high yield under mild conditions. In hydrometallurgy, thiosulfate chemisorption on cobaltiferous pyrite weakens metal–sulfur bonds, facilitating selective Co and Fe leaching while offering a non-toxic alternative to cyanide. Biomedical studies further reveal that the molecule can behave either as a slow-release hydrogen-sulfide donor or as an independent signaling entity, conferring protection against cadmium poisoning in aquaculture, calciphylaxis, and ischemia–reperfusion injury.
Synthesis and Production
Industrial and Laboratory Methods:
Sodium thiosulfate is produced through several chemical processes:
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Sodium Sulfite Method: Reacting sulfur with sodium sulfite in an aqueous solution.
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Oxidation of Sulfide-Containing Liquors: Utilizing by-product liquors from sodium sulfide production or paper/pulp processes (white and black liquor), which are reacted with sulfur dioxide or oxidized to yield sodium thiosulfate.
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Reaction with Sodium Carbonate: Dissolving soda ash (sodium carbonate) and processing it with sulfur-containing compounds.
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Laboratory Synthesis: Reacting sulfur with sodium hydroxide in water.
The most common commercial form is the pentahydrate (Na₂S₂O₃·5H₂O), which is produced by concentrating and crystallizing the resulting solutions from the above methods.
Uses and Applications
Sodium thiosulfate has a remarkably wide range of applications across multiple fields:
1. Medical and Pharmaceutical:
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Established Uses:
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Antidote: For cyanide and arsenic poisoning.
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Cisplatin-Induced Toxicity: Prevention of ototoxicity (hearing loss) in pediatric cancer patients (marketed as PEDMARQSI).
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Calciphylaxis: Treatment of vascular calcification and skin ulcers in patients with end-stage renal disease.
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Antifungal Agent: Topical treatment for skin conditions like tinea versicolor.
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Investigational & Potential Uses:
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Late-Onset Alzheimer's Disease (LOAD): Proposed as a multi-target therapy for its antioxidant, anti-inflammatory, chelating, and neurovascular protective properties.
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Cardioprotection, Stroke, and Vascular Dementia: Leveraging its role as a hydrogen sulfide (H₂S) donor to improve blood flow and reduce cell death.
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2. Industrial:
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Photography: As a "fixer" to dissolve unreacted silver halides from photographic film and paper.
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Water Treatment: For dechlorination and in wastewater purification.
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Mining: As a non-toxic alternative to cyanide for extracting gold and silver from ores.
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Textiles and Leather: As a mordant in dyeing, a reducing agent in chrome tanning, and to reduce color intensity.
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Paper and Pulp: As an "antichlor" to remove excess chlorine after bleaching.
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Consumer Products: Found in cleaning agents, cosmetics, and personal care products.
3. Agricultural:
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Plant Treatment: Foliar application can increase trichome density and alter gene expression in plants (e.g., cucumbers), potentially enhancing pest resistance.
4. Food Industry:
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Food Additive: Used as an antioxidant and sequestrant (INS No. 539), with limitations (e.g., up to 0.1% in salt).
Chemical and Physical Properties
General Information:
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IUPAC Name: disodium;dioxido-oxo-sulfanylidene-λ⁶-sulfane
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Molecular Formula: Na₂O₃S₂
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CAS Number: 7772-98-7
Physical Properties:
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Appearance: White, crystalline solid or powder; colorless monoclinic crystals.
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Molecular Weight: 158.11 g/mol (anhydrous).
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Melting Point: 48.5 °C (pentahydrate decomposes).
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Density: 1.667 g/cm³.
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Solubility: Highly soluble in water (20.9 g/100mL at 20 °C); practically insoluble in alcohol.
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Other: Hygroscopic (absorbs moisture from the air).
Chemical Properties:
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Composition: An inorganic sodium salt composed of a 2:1 ratio of sodium and thiosulfate ions.
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Decomposition: Decomposes upon heating (above ~300 °C), emitting toxic fumes of sulfur oxides and sodium oxide.
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Reactivity: A reducing agent. Can react violently with strong oxidizers (e.g., chlorates, nitrates). Incompatible with acids, which cause decomposition to sulfur and sulfur dioxide.
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Mechanism of Action (Biological): Functions as an antioxidant, anti-inflammatory agent, chelator (binds calcium, iron, copper), and a precursor/donor for hydrogen sulfide (H₂S), which acts as a signaling molecule promoting vasodilation and cellular protection.
Computed Properties:
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Hydrogen Bond Donor Count: 0
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Hydrogen Bond Acceptor Count: 4
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Topological Polar Surface Area: 104 Ų
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Complexity: 82.6
Safety and Handling
Hazards Identification:
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GHS Classification: The majority of safety data sheets report it as "Not Classified" for hazard criteria. The U.S. EPA Safer Choice program labels it as a chemical "of low concern."
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Primary Hazards:
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Decomposition: Heating produces highly toxic fumes of sulfur oxides.
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Dust: A nuisance-causing concentration of airborne particles can be reached quickly.
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Reactivity: Presents a risk of explosion in contact with strong oxidizing agents.
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Safety Measures:
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Handling: Avoid creating dust. Do not eat, drink, or smoke while handling. Use with adequate ventilation.
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Storage: Store separated from strong oxidants in a cool, dry place.
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Personal Protective Equipment (PPE): Wear safety goggles and, if dust is generated, a particulate filter respirator.
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First Aid:
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Inhalation: Move to fresh air.
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Skin Contact: Rinse and wash with water and soap.
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Eye Contact: Rinse with plenty of water for several minutes.
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Ingestion: Rinse mouth.
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Adverse Effects (Medical Use):
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Common side effects include metabolic acidosis, nausea, vomiting, headache, and abdominal cramping, especially if infused too rapidly.
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Long-term use in animal studies suggests a potential risk for osteoporosis.
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Allergic reactions, though rare, are possible.