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Product Name: Methimazole
Chemical Name: 1-Methylimidazole-2-thiol
Synonyms: Tapazole, thiamazole
CAS Number: 60-56-0
Recommended Use: Pharmaceutical intermediate, hyperthyroidism treatment
Manufacturer Information: Available upon request (typically listed with contact details)
Emergency Phone Number: Refer to local emergency services or Poison Control Center
Molecular Formula: C4H6N2S
Molecular Weight: 114.17 g/mol
GHS Classification: Acute toxicity, oral (Category 3); Skin irritation (Category 2); Serious eye irritation (Category 2A)
Signal Word: Danger
Hazard Statements: Toxic if swallowed, causes skin irritation, causes serious eye irritation
Pictograms: Skull and crossbones, exclamation mark
Precautionary Statements: Avoid breathing dust; wash thoroughly after handling; do not eat, drink, or smoke when using; use personal protective equipment as required
Routes of Exposure: Inhalation, ingestion, dermal contact, eye contact
Target Organs: Thyroid gland, skin, eyes
Symptoms: Sore throat, cough, headache, nausea, rash
Component: Methimazole
Chemical Formula: C4H6N2S
Concentration: > 99% by weight
Impurities/Additives: Trace level process residues, typically < 1%
Other Ingredients: No other hazardous ingredients present above cut-off values
Inhalation: Move affected person to fresh air. Seek medical attention if symptoms develop or persist.
Skin Contact: Remove contaminated clothing, rinse skin with plenty of water for at least 15 minutes, call a physician if irritation develops or persists.
Eye Contact: Rinse immediately with copious amounts of water for at least 15 minutes while keeping eyelids open, seek urgent medical care.
Ingestion: Rinse mouth, do not induce vomiting, seek prompt medical attention.
Most Important Symptoms and Effects: Irritation, headache, thyroid dysfunction, allergic reactions.
Advice to Physician: Treat symptomatically and monitor thyroid function; supportive care as needed.
Suitable Extinguishing Media: Water spray, carbon dioxide, dry chemical powder, foam
Unsuitable Extinguishing Media: Direct water stream may spread material
Specific Hazards: Thermal decomposition releases toxic fumes including nitrogen oxides, sulfur oxides
Special Protective Equipment: Firefighters should wear full protective gear and self-contained breathing apparatus
Fire/Explosion Hazards: Not considered highly flammable, but dust can form explosive mixture in air
Advice for Firefighters: Collect contaminated fire water separately, prevent run-off into drains, work from upwind to avoid vapor exposure
Personal Precautions: Evacuate unnecessary personnel, wear protective clothing, avoid dust formation, provide adequate ventilation
Environmental Precautions: Prevent further leakage or spillage if safe to do so, keep away from drains, surface and ground waters
Methods for Cleaning Up: Sweep up with inert material, avoid generating dust, place material in a suitable, labeled closed container for disposal
Reference to Other Sections: See Sections on exposure controls and personal protection
Emergency Procedures: Use nonsparking tools, wash spill area thoroughly after material pickup
Decontamination: Wash affected area with soap and water, properly ventilate space
Precautions for Safe Handling: Handle in a chemical fume hood if possible, avoid breathing dust, direct contact with skin, eyes, and clothing
Advice on General Occupational Hygiene: Wash hands after handling, remove contaminated clothing and protective equipment before eating
Conditions for Safe Storage: Store in a tightly closed, labeled container in a cool, dry, well-ventilated location, separated from incompatible substances such as oxidizers
Storage Temperature: Ambient or as specified by manufacturer; protect from moisture
Special Requirements: Keep container upright, avoid prolonged exposure to light
Incompatible Materials: Strong oxidizing agents, strong acids, alkalis
Occupational Exposure Limits: No specific TLV/PEL established; minimize dust exposure
Engineering Controls: Local exhaust ventilation, eyewash stations, safety showers
Personal Protection Equipment: Chemical-resistant gloves (nitrile, latex), protective clothing, safety goggles, NIOSH/MSHA approved respirator if dust is generated
Hygiene Measures: Wash hands before breaks and after work, avoid eating or drinking in work area, prohibit smoking
Environmental Controls: Avoid release into the environment, use closed systems where feasible
Special Instructions: Use appropriate PPE for specific tasks, ensure regular maintenance of safety equipment
Appearance: White to off-white crystalline powder
Odor: Faint, sulfur-like odor
Odor Threshold: Not determined
pH: Not available in aqueous solution
Melting Point/Freezing Point: 144–146 °C
Boiling Point: Decomposes before boiling
Flash Point: Not applicable
Evaporation Rate: Not available
Flammability: Non-flammable (as supplied)
Upper/Lower Explosion Limits: Not determined
Vapor Pressure: Not significant at room temperature
Vapor Density: Not available
Relative Density: Approximately 1.3 g/cm³
Solubility: Moderately soluble in water, soluble in alcohol
Partition Coefficient (log Kow): -0.15 (estimated)
Auto-ignition Temperature: Not determined
Decomposition Temperature: > 200 °C
Viscosity: Not applicable (solid)
Chemical Stability: Stable under recommended storage and handling conditions
Possibility of Hazardous Reactions: Not expected under normal temperatures and pressures
Conditions to Avoid: Heating to decomposition, exposure to moisture and strong lights
Materials to Avoid: Oxidizing agents, acids, alkalis
Hazardous Decomposition Products: Thermal breakdown yields toxic gases including nitrogen oxides, sulfur oxides, carbon oxides
Reactivity: Low under normal use, can slowly react with strong oxidants
Acute Toxicity: Oral LD50 (rat): 245 mg/kg
Inhalation Toxicity: Data not available; avoid inhalation as it may be harmful to respiratory tract
Skin Corrosion/Irritation: May cause irritation after prolonged or repeated contact
Eye Damage/Irritation: Causes eye irritation; may involve redness, watering, itching
Respiratory Sensitization: Not well documented, possible irritant
Skin Sensitization: May cause allergic skin reactions
Mutagenicity/Genotoxicity: Not classified as a mutagen, but chronic exposure data remain limited
Carcinogenicity: Not listed by IARC, NTP, OSHA
Reproductive Toxicity: Evidence from animal studies shows possible developmental effects at high exposure
Organ Toxicity: Target organ—thyroid gland (inhibits hormone synthesis), other effects in liver, immune system
Potential Chronic Effects: Prolonged exposure could cause alteration of thyroid function, skin sensitization
Ecotoxicity: Acute aquatic toxicity data suggest moderate hazard (LC50 for fish and daphnia believed to be between 1–10 mg/L)
Persistence and Degradability: Readily biodegradable in environment; breakdown occurs in presence of microbes
Bioaccumulative Potential: Low based on partition coefficient
Mobility in Soil: Likely to have moderate mobility due to moderate water solubility
Other Adverse Effects: Discharge in significant quantities can disrupt aquatic organism thyroid regulation
Impact on Sewage Treatment: No substantial removal via standard waste treatment; direct discharges should be limited
Waste Treatment Methods: Dispose of via licensed waste disposal contractor
Disposal of Contaminated Packaging: Empty containers should be triple-rinsed before disposal or recycling
Special Precautions: Do not allow to enter drains, surface water or soil, incinerate in accordance with local regulations
Recommended Waste Code: Dependent on country; often listed as hazardous chemical waste
Regulatory Guidance: Reference local, regional, national, or international regulations for disposal of chemical waste
UN Number: Not classified as hazardous for transportation under most global regulations
Proper Shipping Name: Methimazole
Transport Hazard Class: Not regulated
Packing Group: Not regulated
Environmental Hazards: Not a marine pollutant as packaged for general shipping
Special Transport Precautions: Avoid conditions that might generate dust during transit, ensure secure packaging to prevent leaks or spills
OSHA Status: Regulated as hazardous, requires workplace controls and training
TSCA Inventory: Listed
EC Inventory: Listed (EINECS 200-482-8)
U.S. SARA Title III: Does not appear as a listed substance, monitor for updates
WHMIS Classification (Canada): D2A—very toxic, D2B—irritant
REACH (EU): Pre-registered
Other National Regulations: Subject to chemical inventories and control in multiple jurisdictions for worker and environmental safety
Labeling Requirements: GHS-compliant: signal word, hazard statements, pictograms, precautionary statements on all containers
Chemical Safety Assessment: Necessary for all stages of life cycle as per REACH guidelines
