Methylene blue

Description

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

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

Risks

• 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.
• Insoluble in ether
• pH of aq. solution = 3 - 4.5
• Composition = C16H18N3SCl-3H2O
• CAS = 61-73-4
• Melting Point = 190 C (dec)
• Molecular Weight = 319.85

Resources and Citations

• Wikipedia: Methylene blue Accessed April 2026
• 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 www.colour-index.org