Methylene Blue (C₁₆H₁₈ClN₃S)
Description
Methylene Blue (C₁₆H₁₈ClN₃S), also known as methylthioninium chloride, is a heterocyclic aromatic compound belonging to the phenothiazine class. As a versatile synthetic dye and pharmaceutical compound, it is produced through several industrial synthesis routes:
1. Chemical Synthesis (Primary Production Method):
Oxidation of dimethyl-4-phenylenediamine with dichromate in the presence of hydrogen sulfide
Typical industrial yield: 85-92%
Final purity: ≥97% by UV-Vis spectrophotometry
Crystal form: Dark green powder with bronze luster
2. Purification Processes:
Recrystallization from alcohol/water mixtures
Column chromatography for pharmaceutical grade
Membrane filtration for endotoxin removal
Molecular Characteristics
Molecular weight: 319.85 g/mol
λmax: 664 nm in water (molar extinction coefficient 84,000 M⁻¹cm⁻¹)
Oxidation-reduction potential: +0.01 V (vs NHE)
pKa: 2.6 (tertiary amine), 11.2 (thiazine nitrogen)
Physicochemical Properties
Solubility Profile:
Water: 40 g/L (25°C)
Ethanol: 10 g/L
Chloroform: 2.5 g/L
Insoluble in ether and benzene
Stability Parameters:
pH stability: 3-9 (aqueous solutions)
Photodegradation: Sensitive to UV light
Thermal decomposition: >250°C
Technical specifications (USP grade)
Loss on drying: ≤1.5%
Residue on ignition: ≤0.1%
Heavy metals: ≤20 ppm
Absorbance ratio (A664/A610): ≥3.0
Water content: ≤6% (hydrate form)
Benefits
1. High Chromogenic Potential: Strong visible absorption with distinct color change upon redox
2. Redox Indicator Properties: Reversible oxidation-reduction characteristics
3. Formulation Flexibility: Water and alcohol solubility for diverse preparations
4. Staining Specificity: Selective binding to cellular components
Applications
1. Biological Staining:
Microscopy staining solutions
Vital staining for live cells
Nerve tissue visualization
2. Medical Diagnostics:
Surgical marker solutions
Methemoglobinemia testing
Lymph node mapping
3. Aquaculture:
Antifungal treatments
Water disinfection
Fish disease management
4. Industrial Applications:
Redox indicator in chemical analysis
Dye for textile and paper industries
Battery component in flow cells
Product Processing
