|Molecular formula||C 16 H 18 ClN 3 S|
dark green, shiny crystals
|External identifiers / databases|
|Molar mass||319.86 g mol −1|
approx. 190 ° C (decomposition)
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .|
Methylene blue was first synthesized in 1876 by the chemist Heinrich Caro at BASF . A year later, BASF received the first German Reich patent for a tar dye for methylene blue . Around 1900, methylene blue was also tried as a drug for mental illness. It was not until the 1950s that other phenothiazines ( chlorpromazine ) were discovered as psychotropic drugs.
Methylene blue absorbs light in the range from about 530 to 700 nm; the absorption maximum is 660 nm.
Methylene blue is used as a redox indicator . It is a good hydrogen acceptor that oxidizes alcohols to aldehydes in the presence of platinum . The solution becomes discolored. An analogous reaction can also be carried out with glucose and atmospheric oxygen as a blue bottle experiment . A corresponding redox reaction takes place when diluted sulfuric acid and a little zinc powder are added to a methylene blue solution . Methylene blue is reduced to a colorless leuco form. The colorless solution turns blue again after shaking in air, because the leuco form is oxidized again to methylene blue by the oxygen in the air.
Methylene blue is produced in several steps from N , N -dimethyl- p -phenylenediamine with the addition of dichromate as an oxidizing agent and the addition of N , N -dimethylaniline . Finally it has to be oxidized to the indamine, whereby Bindschedler's green is formed. This is cyclized with hydrogen sulfide in the presence of copper sulfate .
It is used to dye fibers or paper blue. In water, methylene blue dissolves well with an intense blue color (hence the name), even small amounts cause a visible coloration of the water.
In histology , it was in 1885 for the first time by Paul Ehrlich certain selective staining tissues (especially the gray matter in the peripheral nervous system ) is used. Coloring with methylene blue is possible on the living organism ( vital coloring ), which is why it is one of the so-called vital coloring substances.
In molecular biology , methylene blue is used to stain DNA and RNA in gels and on membranes after blotting . Although methylene blue is not as sensitive as ethidium bromide , it is less toxic and it does not intercalate into the nucleic acid chains.
In medicine , it is an important antidote for nitrite and aniline poisoning, as it accelerates the conversion of methemoglobin back to functional hemoglobin (see methemoglobinemia ). It is also used as an antiseptic , to fight malaria , anti-rheumatic and for diagnostic purposes. In veterinary medicine, it is used together with malachite green as a remedy for the white spot disease that occurs in fish .
The versatile dye is also being investigated for its suitability for treating chronic lower back pain . The methylene blue is injected between the vertebrae directly into the damaged intervertebral discs (lat. Discus intervertebralis ), which destroys the pain receptors and thus eliminates or alleviates the pain. Preliminary results of the in a placebo -controlled clinical study conducted study are very encouraging: This simple, minimally invasive and inexpensive method of treatment results in a majority of patients to a sustainable, lasting for at least two years pain relief, with no patients complications occurred . Subsequent studies yielded partly contradicting results. The treatment method has not yet been approved .
Methylene blue is neurotoxic in certain concentrations . The use of methylene blue can lead to serotonin syndrome when using MAO inhibitors such as B. methylene blue and antidepressants of the group selective serotonin reuptake inhibitors (SSRI), such as fluoxetine , fluvoxamine , paroxetine , sertraline and citalopram can be combined.
In wastewater analysis , a methylene blue sample is used to determine the putrefactive properties. The methylene blue sample can be used to prove whether and to what extent the effluent of a sewage treatment plant still contains putrefactive substances. Methylene blue is a redox indicator and becomes discolored with absolute exclusion of air to the extent to which anaerobic conditions (H 2 S formation) take over. The time taken for the dye added to the sample to decolorize is determined. 0.6 ml of a methylene blue solution (0.05%) is added to a 100 ml ground-glass stopper bottle, filled to the brim with sample, the stopper is attached without bubbles and is kept in the dark at 20 ° C (incubator). The sample is observed daily (several times on the first day) and determines the time until discoloration; if this occurs on the first day (details in hours) or within four days (details in days), the process quality is not permitted; if no discoloration occurs within five days, the sample is designated as "ne" (not discolored) and the test is terminated (see DEV , H 22, "Test for putrefaction" and ÖNORM M 6276).
In biochemistry, methylene blue is used as a redox mediator. The half-value potential E 0 'is +0.011 mV.
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