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5-Amino-2-benzimidazolethiol
1. Basic Information
Name: 5-Amino-2-benzimidazolethiol
Alias: 5-Amino-1H-benzimidazole-2-thiol, 2-Mercapto-5-aminobenzimidazole
CAS No.: 2818-66-8
Molecular Formula: C7H7N3S
Molecular Weight: 165.22
Category: Amino mercapto benzimidazole fused heterocyclic pharmaceutical & corrosion inhibitor intermediate
2. Physical and Chemical Properties
Physical Properties
- Appearance: Off-white to pale gray crystalline powder
- Odor: Faint sulfur mercaptan odor
- Solubility: Soluble in dilute acid, dilute alkali, DMSO, hot DMF; slightly soluble in hot methanol/ethanol; insoluble in cold water, aliphatic hydrocarbons
- Melting Range: 270–276 °C (decomposes with sulfur-containing gas release)
- Hygroscopy: Slightly hygroscopic under high humidity
- Aqueous Property: Amphoteric compound; thiol group weakly acidic, amino group weakly alkaline
Chemical Properties
- Molecular Structure: Benzimidazole core with amino substituent at C5 and mercapto (-SH) at C2; tautomerism exists between thiol and thione
- Mercapto reactivity: Undergoes S-alkylation, disulfide oxidative coupling, metal chelation; easily oxidized to disulfide in air
- Amino group reactivity: Capable of diazotization, acylation, condensation to construct drug side chains and dye chromophores
- Imidazole ring characteristic: Forms stable coordination complexes with transition metal ions (Cu, Zn, Ag)
- Thermal Stability: Stable below 240 °C; high-temperature decomposition releases toxic sulfur fumes
- Photostability: Highly light-sensitive; UV irradiation accelerates oxidation and darkens to gray-black
- Compatibility: Compatible with polar aprotic solvents; incompatible with strong oxidants, heavy metal salts, hydrogen peroxide
3. Main Application Fields
1. Pharmaceutical Synthetic Intermediate (Core Application)
Key raw material for anti-ulcer, anti-fungal, anti-parasitic benzimidazole APIs; mercapto group serves as core binding site for target enzyme inhibition
2. Metal Corrosion Inhibitor
Organic thiol chelating agent for copper, steel, alloy anti-rust treatment in cooling water and metal surface treatment
3. Dye & Fluorescent Probe Intermediate
Precursor for sulfur-containing heterocyclic azo dyes and metal ion fluorescent detection probes
4. HPLC Reference Standard
Chromatographic standard for benzimidazole thiol intermediate purity testing
4. Quality Specification Table
| Test Item | Standard Specification |
| CAS Number | 2818-66-8 |
| Molecular Formula | C7H7N3S |
| Appearance | Uniform pale off-white powder without black oxidized impurities |
| HPLC Purity | Pharma Grade ≥99.0% |
| Water Content (KF) | ≤0.30% |
| Melting Decomposition Range | 270–276 °C |
| Disulfide Oxide Impurity | ≤0.20% |
| Residue on Ignition | ≤0.10% |
| Single Unknown Impurity | ≤0.10% |
| Heavy Metals (Pb) | ≤10 ppm |
| Packaging | Nitrogen-purged amber vacuum aluminum foil bags / PE-lined fiber drums |
| Storage Condition | Hermetically sealed cool dark warehouse below 25 °C; isolate from air, light and oxidants to prevent oxidation |
| Transportation Requirement | Light-sensitive sulfur heterocyclic solid, light-proof sealed packaging |
| Shelf Life | 18 months under nitrogen-filled vacuum sealed storage |
Safety Warning
Irritant sulfur-containing heterocyclic powder. Dust irritates eyes, respiratory tract and skin; mercaptan vapor causes nasal discomfort and headache. All operations must be carried out in ventilated fume hoods with dust respirators and chemical-resistant gloves. Avoid exposure to air/UV light to prevent oxidation; prohibit mixing with strong oxidants to avoid violent redox reaction. Waste liquid recovered by solvent distillation and neutralized; solid waste classified as sulfur-containing organic hazardous waste and disposed by licensed professional hazardous waste institutions.
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