Methylene blue

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Dark green crystals that form a deep blue aqueous solution. Methylene blue was first prepared in 1876 by Caro. It is a synthetic Aniline dye that was used a lightfast colorant for Cotton, Silk, and Wool (often with zinc as a mordant). Methylene blue is used as a biological stain for bacteria and as an indicator in oxidation-reduction reactions. Methylene blue is also used as a Disinfectant and an antidote for cyanide poisoning.

Chemical structure

Methylene blue.jpg

Synonyms and Related Terms

methylthionine chloride; Basic Blue 9; CI 52015; Solvent Blue 8; 3,7-bis(dimethylamino)phenothiazin-5-ium chloride; azul de metileno (Esp.); azul de metileno (Port.); methyl blue; solvent blue; Basic Lake Blue; Swiss blue


  • Toxic by ingestion and inhalation.
  • Contact may cause irritation.
  • Potential teratogen.
  • Flammable. Flash point = 178 C
  • Fisher Scientific: MSDS

Physical and Chemical Properties

Soluble in water, ethanol, chloroform. pH of aq. solution = 3 - 4.5

Insoluble in ether.

Composition C16H18N3SCl-3H2O
CAS 61-73-4
Melting Point 190 C (dec)
Molecular Weight mol. wt. = 319.85

Resources and Citations

  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 6137
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • A.Scharff, 'Synthetic dyestuffs for textiles and their fastness to washing', ICOM-CC Preprints Lyon, Getty Conservation Institute, Los Angeles, 1999
  • Colour Index International online at

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