Merbromin (27-18-8) Physical and Chemical Properties
Merbromin
Organomercuric disodium fluorescein salt historically used as a topical antiseptic and fluorescent marker, of interest for formulation, QC and analytical applications.
| CAS Number | 27-18-8 |
| Family | Organomercuric fluorescein salt |
| Typical Form | Powder or aqueous solution |
| Common Grades | EP |
Merbromin is an organomercuric fluorescein derivative that exists as a disodium salt of a mercurated xanthene (molecular formula \(\ce{C20H8Br2HgNa2O6}\)). Structurally it is a dibromo-substituted fluorescein core in which a mercuric moiety is covalently bonded to the xanthene framework; the compound is isolated and handled as a mixed ionic species (disodium salt with associated hydroxide/hydrate components). The presence of heavy-atom bromine and mercury centers produces strong visible absorption and fluorescence quenching characteristics typical of halogenated, metal-substituted xanthenes; the large, polar anionic framework combined with sodium counterions defines its solid-state and solvation behaviour.
Electronically, the molecule contains delocalized xanthene π-systems conjugated to carbonyl and phenoxide/oxido functions that stabilize the organomercury linkage. Acid–base behaviour is dominated by deprotonated carboxylate and phenolate/oxido groups in the disodium salt form; the salt form increases aqueous ionization and water solubility relative to the neutral fluorescein derivative. As an organomercurial, it is chemically distinct from simple organic dyes: it is more reactive toward soft nucleophiles (sulfur-containing ligands) and has potential to undergo ligand exchange or cleavage under strongly nucleophilic or reductive conditions. Photochemical and oxidative degradation pathways are relevant for formulation stability because the xanthene chromophore can undergo photooxidation and dehalogenation under prolonged light exposure.
Historically, merbromin has been used as a topical antiseptic/antimicrobial dye in first-aid applications (trade name Mercurochrome); regulatory actions have removed or limited its marketed use in several countries because of concerns over systemic mercury exposure from organomercury compounds. Common commercial grades reported for this substance include: EP.
Basic Physical Properties
Merbromin is an ionic organomercury disodium salt with significant molecular mass and polar surface area. The computed molecular weight is 750.7 \(\mathrm{g}\,\mathrm{mol}^{-1}\). The compound contains heavy atoms (bromine and mercury) that dominate mass and influence physical properties such as density and light absorption; no experimental density, melting point or boiling point values are available in the current data context.
Solubility and Hydration
No experimentally established value for aqueous solubility is available in the current data context. Qualitatively, the disodium salt form increases aqueous solubility compared with the neutral fluorescein parent: ionized carboxylate and phenoxide/oxido groups stabilize the anionic form in water and are balanced by sodium counterions. Preparations sold for topical use are typically formulated as aqueous or alcohol-containing solutions; the chemistry and ionic composition indicate hygroscopicity and possible presence of coordinated water in commercial materials (component listing includes water as a formulation/component).
Thermal Stability and Decomposition
No experimentally established value for decomposition temperature or melting point is available in the current data context. As an organomercury compound, thermal degradation can liberate mercury-containing species and produce complex decomposition products; loss of organic fragments and volatilization of mercury oxides or vapours is a plausible hazard under high-temperature conditions. Dry heating, incineration or any process that can volatilize mercury should be avoided or conducted only under controlled industrial waste-handling procedures.
Chemical Properties
The chemical behaviour of merbromin is governed by the organomercury linkage to the xanthene framework, halogen substituents, and multiple oxygen-based donor sites.
Complex Formation and Coordination
The mercuric centre in merbromin is formally coordinated to oxygen-containing functionalities of the fluorescein-like scaffold, producing a stable organomercury moiety in the salt. The molecule can interact with soft nucleophiles (thiols, sulfides) and strong ligand donors that preferentially bind mercury; such ligand-exchange reactions can displace the existing Hg–O linkage and produce mercury–sulfur or mercury–nitrogen complexes. In environmental or biological matrices, complexation with sulfhydryl groups in proteins and thiol-containing ligands governs bioavailability and toxicity.
Reactivity and Stability
Merbromin's xanthene chromophore confers strong visible absorption and fluorescence, but the molecule is susceptible to photochemical degradation and oxidative changes of the chromophore under sustained light or oxidizing conditions. The organomercury bond is relatively stable in neutral aqueous media but is vulnerable to nucleophilic attack, reductive cleavage or transmetalation under strongly nucleophilic, reducing, or acidic conditions. Hydrolysis under standard conditions is not rapid, but chemical or biological processes can mobilize mercury from the organometallic framework, with implications for toxicity and environmental persistence.
Molecular Parameters
Molecular Weight and Composition
- Molecular formula: \(\ce{C20H8Br2HgNa2O6}\)
- Molecular weight: 750.7 \(\mathrm{g}\,\mathrm{mol}^{-1}\)
- Exact mass: 751.81690 (as provided)
- Monoisotopic mass: 749.81895 (as provided)
- Heavy atom count: 31
Additional computed descriptors: - Topological polar surface area (TPSA): 90.5 - Complexity: 799 - Formal charge: 0 - Covalently-bonded unit count: 4
LogP and Ionization State
No experimentally established value for logP (octanol–water partition coefficient) is available in the current data context. Ionization state and ionic form are, however, well described: merbromin is isolated as a disodium salt of the mercurated xanthene with deprotonated carboxylate and oxido/phenolate functionalities. The formal charge for the molecular assembly is 0 in the disodium salt form, but local anionic centers and sodium counterions confer strong aqueous ionicity and reduced lipophilicity relative to the neutral fluorescein parent.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS RN: 27-18-8
- UNII: M0T18YH28D
- DrugBank ID: DB13392
- Metabolomics Workbench ID: 154203
- NCI Thesaurus Code: C82319
- InChIKey: SQFDQLBYJKFDDO-UHFFFAOYSA-K
- InChI: InChI=1S/C20H9Br2O5.Hg.2Na.H2O/c21-13-5-11-17(7-15(13)23)27-18-8-16(24)14(22)6-12(18)19(11)9-3-1-2-4-10(9)20(25)26;;;;/h1-7,24H,(H,25,26);;;;1H2/q;3*+1;/p-3
- SMILES:
C1=CC=C(C(=C1)C2=C3C=C(C(=O)C=C3OC4=C(C(=C(C=C24)Br)[O-])[Hg+])Br)C(=O)[O-].[OH-].[Na+].[Na+] - IUPAC name: disodium;[2,7-dibromo-9-(2-carboxylatophenyl)-3-oxido-6-oxoxanthen-4-yl]mercury(1+);hydroxide
Synonyms and Structural Names
Representative synonyms and historical names (selected from available depositions and thesauri): - Merbromin - Mercurochrome - Merbromine - Merbromin sodium - 2,7-Dibromo-4-Hydroxymercurifluoresceine - Disodium 2',7'-dibromo-4'-(hydroxymercury)fluorescein - Disodium (2,7-dibromo-9-(2-carboxylatophenyl)-6-oxido-3-oxo-3H-xanthen-5-yl)mercurol - Merbromina; Merbrominum - Flavurol; Fluorochrome; Chromargyre; Gallochrome; Fluo[r]escent Dye (historical descriptors)
(These synonyms reflect nomenclatural variants and trade/curation names encountered in the literature and regulatory/chemical registries.)
Industrial and Commercial Applications
Merbromin has historically been used primarily as a topical antiseptic and wound antiseptic dye due to its bacteriostatic activity and prominent red/orange staining and fluorescence. Its ATC classification places it among mercurial dermatological antiseptics. Use has diminished or been discontinued in multiple regulatory jurisdictions because of the presence of organomercury, and alternative non-mercurial antiseptics are commonly preferred for first-aid and dermatological applications.
Use as Salt Form or Excipient
Merbromin is supplied as the disodium salt to maximize aqueous solubility and to stabilize the deprotonated xanthene chromophore. Formulated products have typically been aqueous or alcohol-based solutions intended for topical application; the disodium salt and associated hydroxide/hydrate components influence pH and solvation behaviour in formulations. No specific pharmaceutical-grade specifications are provided here.
Representative Use Cases
- Topical first-aid antiseptic solutions and ointments (historical use).
- Topical veterinary antiseptic preparations in some contexts (as indicated by veterinary classification).
- Use as a fluorescent dye or tracer in some laboratory or demonstration contexts has been reported historically, arising from the xanthene fluorophore characteristics.
If no current authorized applications are available in a given jurisdiction, selection of alternatives should be based on the risk profile and the general properties described above.
Safety and Handling Overview
The presence of a covalently bound organomercury center distinguishes merbromin from simple organic dyes and requires special attention to toxicity, environmental persistence and waste management.
Toxicological Considerations
Merbromin is an organomercury compound and therefore carries the inherent toxicological concerns of mercury-containing organics: potential for systemic absorption, accumulation of mercury species, and adverse effects associated with mercury exposure. Skin contact, mucous membrane exposure, or ingestion can lead to local irritation and, with sufficient exposure, systemic effects typical of mercury compounds. The compound can bind to thiol groups in biological macromolecules, and mobilisation of mercury from the organomercury structure is a primary driver of toxic effects. Use on broken skin or prolonged topical application increases exposure risk; regulatory restriction or withdrawal in several countries reflects these safety considerations.
For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
Storage and Handling Guidelines
- Store in a tightly closed container, protected from light and heat, in a cool, well-ventilated area to minimize photodegradation and volatilization risks.
- Handle using appropriate personal protective equipment (gloves, eye protection, lab coat); avoid skin contact, inhalation of dust or aerosols, and ingestion.
- Prevent releases to the environment; organomercury compounds are persistent and pose environmental hazards to aquatic and terrestrial systems.
- Waste and surplus material must be treated as mercury-containing hazardous waste and disposed of according to local regulations and approved hazardous-waste procedures; do not incinerate or release to sewer without appropriate controls.
For product-specific handling limits, exposure controls and emergency measures consult the manufacturer’s SDS and applicable occupational exposure guidelines.
