5-Amino-2-mercaptobenzimidazole: Properties, Uses & Lab Guide
5-Amino-2-mercaptobenzimidazole: Properties, Uses & Lab Guide
5-Amino-2-mercaptobenzimidazole is a bifunctional heterocyclic compound bearing both a primary amine and a thiol group on a benzimidazole scaffold, making it a versatile building block in medicinal chemistry, materials science, and analytical research.
- CAS Number
- 1123-80-4
- Molecular Formula
- C7H7N3S
- Molecular Weight
- 165.21 g/mol
- Functional Groups
- Primary amine (–NH2) and thiol/thione (–SH / C=S)
- Appearance
- Off-white to pale yellow crystalline solid
- Key Applications
- Pharmaceutical synthesis, coordination chemistry, corrosion inhibition, sensor development
Chemical Structure and Physical Properties
5-Amino-2-mercaptobenzimidazole (CAS 1123-80-4) is a benzimidazole derivative with the molecular formula C7H7N3S and a molecular weight of approximately 165.21 g/mol. Its structure consists of a fused bicyclic benzimidazole ring system substituted with an amino group at the 5-position and a mercapto (thiol) group at the 2-position.
The compound commonly exists in a thione tautomeric form in the solid state, where the sulfur bears a double bond character (C=S) rather than a free thiol (–SH). In solution, an equilibrium between tautomers may be observed depending on solvent and pH. The compound appears as an off-white to pale yellow crystalline powder. It has limited solubility in water but dissolves in polar aprotic solvents such as DMSO and DMF, as well as in dilute aqueous acid or base due to protonation or deprotonation of its functional groups.
The coexistence of the nucleophilic amine, the thiol/thione sulfur, and the basic imidazole nitrogens grants the molecule multiple coordination and reaction sites, underpinning its broad utility.
Synthesis and Reactivity
5-Amino-2-mercaptobenzimidazole can be prepared from 1,2-diaminobenzene derivatives and carbon disulfide (CS2) under basic conditions, a classical route to 2-mercaptobenzimidazoles. Starting from 3,4-diaminoaniline (o-phenylenediamine bearing an extra amino substituent), cyclization with CS2 furnishes the target compound. Alternative routes employ thiocarbonyl equivalents or involve nitro-group reduction of a preformed 2-mercaptobenzimidazole-5-nitro precursor.
The bifunctional nature of 5-amino-2-mercaptobenzimidazole makes it highly reactive toward a variety of electrophiles. The amine group participates in acylation, sulfonylation, reductive amination, and Schiff base formation. The thiol/thione group undergoes S-alkylation, S-acylation, and oxidative coupling. These dual reactivities are exploited in the synthesis of pharmacologically active heterocycles, including thiadiazines, triazines, oxadiazoles, and thiazolidinones fused to or derived from the benzimidazole core.
Researchers should note that the free thiol form is susceptible to aerial oxidation; storage under inert atmosphere or with appropriate antioxidants is advisable to maintain reagent integrity.
Biological Activity and Pharmaceutical Applications
The benzimidazole nucleus is a privileged scaffold in drug discovery, and 5-amino-2-mercaptobenzimidazole has attracted attention as a pharmacophore and as an intermediate in the synthesis of bioactive compounds. Derivatives of this compound have been investigated for antimicrobial, antifungal, anti-inflammatory, anticancer, and antiviral properties in the scientific literature.
The amino and thiol groups provide handles for generating diverse libraries of compounds. For example, Schiff bases formed between the amine and aromatic aldehydes, or thiazolidinone rings closed through the thiol group, have shown activity against bacterial and fungal pathogens in reported studies. The metal-chelating ability of the molecule, via the nitrogen and sulfur donors, is also of interest in the design of metallodrug candidates.
As a research reagent, 5-amino-2-mercaptobenzimidazole (A151156) is supplied by Aladdin Scientific to support exploratory medicinal chemistry and hit-to-lead optimization programs. Researchers are advised to validate bioactivity data using appropriate positive controls and orthogonal assays.
Materials Science and Analytical Applications
Beyond pharmaceutical research, 5-amino-2-mercaptobenzimidazole finds utility in materials science and analytical chemistry. The compound is recognized as a corrosion inhibitor scaffold: the ability of its nitrogen and sulfur atoms to adsorb onto metal surfaces and form protective layers makes it relevant to the design of inhibitors for copper, steel, and other metals in acidic environments.
In coordination chemistry, the compound acts as a polydentate ligand, forming stable complexes with transition metals such as copper(II), nickel(II), cobalt(II), and zinc(II). These metal complexes are studied for their structural diversity, magnetic properties, and potential catalytic or biological activity.
In analytical and sensor applications, 5-amino-2-mercaptobenzimidazole has been employed in the fabrication of chemically modified electrodes and as a receptor molecule for heavy-metal ion detection, leveraging its strong affinity for soft metal centers. Its use in surface functionalization of gold nanoparticles and self-assembled monolayers has also been reported, exploiting the thiol group for chemisorption onto gold surfaces.
Handling, Storage, and Safety Considerations
5-Amino-2-mercaptobenzimidazole should be handled in accordance with standard laboratory safety practices for organic thiol compounds. Work in a well-ventilated fume hood is recommended, as thiol-containing compounds can generate odorous decomposition products. Personal protective equipment including nitrile gloves, laboratory coat, and safety glasses should be worn at all times during handling.
The compound should be stored in a tightly sealed container, away from oxidizing agents, strong acids, and strong bases, at cool and dry conditions (typically 2–8 °C or room temperature per supplier specification). Exposure to air and moisture should be minimized to prevent oxidative dimerization of the thiol group.
Disposal must comply with local regulations for organic sulfur-containing compounds. Consult the Safety Data Sheet (SDS) for A151156 provided by Aladdin Scientific for complete hazard information, first-aid measures, and regulatory classifications before use. This compound is intended for research use only and is not approved for use in humans or animals.
Frequently asked questions
What is the difference between the thiol and thione forms of 5-Amino-2-mercaptobenzimidazole?
5-Amino-2-mercaptobenzimidazole exists as two tautomers: the thiol form (–SH at C-2) and the thione form (C=S at C-2 with N–H). In the solid state, the thione tautomer predominates, as confirmed by spectroscopic and crystallographic data reported in the literature. In solution, the tautomeric ratio depends on solvent polarity and pH.
What solvents are recommended for dissolving 5-Amino-2-mercaptobenzimidazole in the laboratory?
The compound has low solubility in water at neutral pH. DMSO and DMF are the most commonly used solvents for preparing stock solutions for biological or chemical assays. Dilute aqueous HCl or NaOH can also be used, as protonation or deprotonation of the functional groups improves aqueous solubility. Ethanol and methanol offer moderate solubility.
How should 5-Amino-2-mercaptobenzimidazole (A151156) be stored to maintain purity?
Store the compound in a tightly closed container under cool, dry conditions and away from light, strong oxidants, and moisture. The thiol group is susceptible to oxidative dimerization upon prolonged exposure to air, which can reduce purity over time. Storing under an inert gas blanket (e.g., nitrogen or argon) is advisable for long-term storage. Always refer to the Aladdin Scientific SDS for A151156 for specific storage conditions.
What types of reactions can be performed using the amino group of 5-Amino-2-mercaptobenzimidazole?
The primary amine at the 5-position can participate in a wide range of reactions including acylation with acid chlorides or anhydrides, sulfonylation, reductive amination with aldehydes, formation of Schiff bases (imines) with carbonyl compounds, and cyclization reactions to form heterocyclic rings such as oxadiazoles, triazines, and thiadiazines. These transformations make the compound a versatile scaffold for building diverse compound libraries.
References
- Clayden, J.; Greeves, N.; Warren, S. Organic Chemistry, 2nd ed.; Oxford University Press: Oxford, 2012. (General reference for heterocyclic chemistry and thiol reactivity.)
- Supuran, C. T.; Scozzafava, A. Benzoic acid and benzene sulfonamide derivatives with strong carbonic anhydrase inhibitory properties and antibacterial/antifungal activity – relevance for benzimidazole scaffold. (General reference for benzimidazole pharmacology.)
- Aladdin Scientific. Product Datasheet: 5-Amino-2-mercaptobenzimidazole, SKU A151156. Aladdin Scientific, Shanghai.
Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.
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