What is "methylene blue"

Methylene \Meth"yl*ene\, n. [F. m['e]thyl[`e]ne, from Gr. ? wine + ? wood; -- a word coined to correspond to the name wood spirit.] (Chem.) A divalent hydrocarbon radical, -CH2-, not known in the free state, but regarded as an essential residue and component of certain derivatives of methane; as, methylene bromide, CH2Br2; -- formerly called also methene.

Methylene blue (Chem.), an artificial dyestuff consisting of a complex sulphur derivative of diphenyl amine; -- called also pure blue.

n. (context organic compound English) A heterocyclic aromatic chemical compound with many uses in biology and chemistry.

n. a dark green dye used as a stain, an antiseptic, a chemical indicator, and an antidote in cyanide poisoning [syn: methylthionine chloride]

Methylene blue (CI 52015), also known as methylthioninium chloride, has many uses in biology and chemistry; for example, it can be used as a stain and as a medication. Methylene blue should not be confused with methyl blue, another histology stain, new methylene blue, nor with the methyl violets often used as pH indicators.

Methylene blue is a heterocyclic aromatic chemical compound (a phenothiazine derivative) with the chemical formula C H N S Cl. At room temperature it appears as a solid, odorless, dark green powder, that yields a blue solution when dissolved in water. The hydrated form has 3 molecules of water per unit of methylene blue. Methylene blue has a pHa of 3 in water(10g/l) at 25 °C (77 °F).

Methylene blue was first prepared as a stain in 1876 by German chemist Heinrich Caro.Badische Anilin- und Sodafabrik [BASF] (Mannheim, Germany), "Verfahren zur Darstellung blauer Farbstoffe aus Dimethylanilin und anderen tertiaren aromatischen Monaminen" (Method for preparation of blue dyes from dimethylaniline and other tertiary aromatic monoamines), Deutsches Reich Patent no. 1886 (December 15, 1877). Available on-line at: P. Friedlaender, Fortschritte der Theerfarbenfabrikation und verwandter Industriezweige (Progress of the manufacture of coal-tar dyes and related branches of industry), volume 1 (Berlin, Germany: Julius Springer, 1888), pages 247-249.
See also:

• British patent no. 3751 (October 9, 1877).
• Heinrich Caro, U.S. Patent no. 204,796 (filed: March 28, 1878 ; issued: June 11, 1878). However, it was discovered to be an antidote to carbon monoxide poisoning and cyanide poisoning in 1932 by Matilda Moldenhauer Brooks.

It is on the World Health Organization's List of Essential Medicines.