Methylene blue

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Not to be confused with methyl blue.
Methylene blue
Methylene blue sample solution.jpg
Methylene blue in solid form and as aqueous solution.
IUPAC name
[7-(Dimethylamino)phenothiazin-3-ylidene]-dimethylazanium chloride
Systematic IUPAC name
3,7-bis(Dimethylamino)-phenothiazin-5-ium chloride
Other names
Basic blue 9
Calcozine blue ZF
CI 52015
Leather pure blue HB
Methylthioninium chloride
Molar mass 319.85 g/mol
Appearance Dark green crystals (solid)
Deep blue (aq. solution)
Odor Weak "skin-like" odor
Density 1.757 g/cm3 (20 °C)
Melting point 100 to 110 °C (212 to 230 °F; 373 to 383 K) (decomposes)
Boiling point Decomposes
4.36 g/100 ml (25 °C)
Solubility Soluble in glacial acetic acid, chloroform, ethanol, glycerol
Slightly soluble in pyridine
Insoluble in diethyl ether, oleic acid, xylene
Vapor pressure 1.3·10-7 mm Hg at 25 °C
Acidity (pKa) 3.8
Safety data sheet FisherSci
Lethal dose or concentration (LD, LC):
1180 mg/kg (rat)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Methylene blue, also known as methylthioninium chloride is an organic chemical compound, a phenothiazine derivative with the chemical formula C16H18N3SCl, with many uses in in medicine, biology and chemistry.

Methylene blue should not be confused with methyl blue, which is also a histology stain, or new methylene blue.



Methylene blue dissolves in water to form a deep blue solution.


Methylene blue is a dark green (or black-green) solid, slightly soluble in water, where it gives a deep blue solution. The solid in commonly encountered as a trihydrate. It is more soluble in glacial acetic acid, chloroform, ethanol. It has a weak odor, reminiscent to some individuals of organic tissues, like skin.


Solid methylene blue is sold by various chemical suppliers and can also be purchased online.

1% aqueous solution is available from pharmacies or pet shops.


Methylene blue can be prepared by treating dimethyl-4-phenylenediamine with hydrogen sulfide dissolved in hydrochloric acid, followed by oxidation with ferric chloride.

However, it's much cheaper to simply buy the compound.


  • Anti-microbial agent
  • Cyanide and carbon monoxide poisoning antidote
  • Biological staining
  • Blue bottle experiment
  • Sulfide analysis
  • Methylene blue value of fine aggregate
  • Peroxide generator



Methylene blue has low toxicity, but it stains blue almost everything it touches.


In closed amber bottles, away from light, as light degrades methylene blue.


No special disposal is required.


Relevant Sciencemadness threads