What is Methylene Blue Definition Formula Preparation and Uses
Methylene blue is a colorful organic chloride salt compound used in medicine and by biologists as a dye to help them see under the microscope. It is also known as Methylthioninium chloride or Swiss blue. It is represented by the formula \[C_{16}H_{18}CIN_{3}S\]. It was discovered in the year 1876 by German chemist Heinrich Caro. Historically, it has been widely used in Africa for treating malaria, but now it has been disapproved when chloroquine and other drugs entered the market. Its molecular weight is 319.85 g/mol. It can cause damage to RBCs and also decreases the ability of the blood to carry oxygen which is the primary health concern of humans when exposed to methylene blue via oral or intravenous means. Methylene blue is a thiazine dye that is basic in nature. Methylene blue stains negatively charged cell components like nucleic acids.
Structure of Methylene Blue
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Structure of Methylene Blue\[C_{16}H_{18}CIN_{3}S\]
Formula of Methylene Blue
Methylene blue is represented by the formula \[C_{16}H_{18}CIN_{3}S\]. It has 3,7-bis(dimethylamino) phenothiazine - 5 - ium as the counterion. Its IUPAC name is
7−(dimethylamino)phenothiazin−3−ylidene
7−(dimethylamino)phenothiazin−3−ylidene - methyl azanium; chloride.
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Preparation of Methylene Blue
Methylene blue is prepared by the oxidation of dimethyl-4-phenylenediamine in the presence of sodium thiosulfate.
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By treating the solution of N, N-dimethyl-p-phenylenediamine and N, N, -dimethylaniline hydrochlorides with \[H_{2}S\] and \[FeCl_{3}\] or another suitable oxidizing agent.
By oxidation of p- amino dimethyl aniline with ferric chloride in the presence of hydrogen sulphide. The dye is zinc chloride double salt of the chloride.
N, N-Dimethyl - p - phenylenediamine reacts with sodium thiosulfate to produce thiosulfuric acid which then condenses with N, N-dimethylaniline when it comes in the presence of \[Na_{2}Cr_{2}O_{7}\] or sodium dichromate to form the indamine, then with copper sulphate and sodium dichromate to the methylene blue.
Related Compounds to Methylene Blue
Methylene Blue cation
Azure A
Azure B
Methylene green
3-(Dimethylamino)-7-(methylamino)phenothiazin-5-ium
3,7-Bis(dimethylamino)-4-nitro phenothiazine-5-ium
Properties of Methylene Blue
Methylene blue is deep blue in colour.
Methylene blue exhibits antioxidant properties.
It also exhibits the property of antidepressants.
It is highly soluble in water, chloroform, ethanol, and glacial acetic acid.
It is insoluble in ethyl ether, xylene, and oleic acid.
It also has the property of being antimalarial.
It gets decomposed while heating and emits toxic fumes of nitrogen oxides, sulphur oxides, and chlorides.
It is non-carcinogenic in nature.
It is slightly soluble in pyridine.
It is basic in nature. It's a basic thiazine dye.
It also exhibits cardioprotective properties.
It is non-combustible in nature.
It acts as the enzyme inhibitor.
What is the Role of Methylene Blue in the Field of Chemistry?
Methylene blue is widely used in the field of chemistry as a redox indicator in analytical chemistry, that is, to detect the presence or absence of oxygen and other oxidising agents due to the change in colour of the solution to blue when an electron is taken from methylene blue. Also, methylene blue is further used in the analysis of volumetric titrations and in Fehling’s test.
What is the Role of Methylene Blue in the Field of Biology?
Apart from chemistry, methylene blue is also used by biologists in various biological experiments as a stain, for example, for identification and visualisation of bacteria, for identification of nucleic acids, that is, DNA and RNA, or in the techniques of northern blotting or as an alternative to crystal violet chemical and ethidium bromide used in the technique of western blotting. Apart from this, methylene blue is also used to calculate the percentage of viable cells in a yeast sample.
What is the Role of Methylene Blue in the Field of Aquaculture?
The use of methylene blue is not restricted to the only chemical and medicinal field but has also been proved to be very useful in the field of aquaculture for the prevention of bacterial and fungal infections on the eggs of freshwater fish. It also increases the oxygen-carrying capacity of fish’s hemoglobin or for the treatment of fish infected with parasitic protozoan.
Uses of Methylene Blue
Methylene blue is used in aqua farming for treating fungal infections.
It is used as an antiseptic in cases of urinary tract infections.
It is also used as an indicator during the different chemical reactions.
It is also used for the treatment of Methemoglobinemia.
It is also used to dye paper and office supplies, but also to tone up silk colours.
It is also used in the treatment of septic shock and anaphylaxis.
It is also used as a dye for a number of staining procedures.
It is also used as a temporary hair colorant.
It is used as an oxidation-reduction agent in different chemical reactions.
It is used in the treatment of pediatric and adult patients with methemoglobinemia.
It is used as a reagent in oxidation-reduction titrations in volumetric analysis.
It is used in the treatment of hypoxia.
It is used for dyeing cotton and wool.
Earlier methylene blue was used to check whether the pasteurized milk is bacteria-free or not. If the colour remains blue, that means milk is pasteurized properly, or else if blue colour disappears that means bacteria is consuming oxygen and the milk is not pasteurized properly.
What are the Warnings Associated with Methylene Blue when it is Used as a Component of a Drug?
Though methylene blue is widely used as a drug, there are certain risk factors associated with its use, due to which there are certain warning labels associated with it. The injections of methylene blue in combination with serotonergic drugs can lead to the serious serotonergic syndrome. Large doses of methylene blue can lead to vomiting, nausea, abdominal pain, dizziness, precordial pain, profuse sweating, headache, hypertension, dyspnea, urinary tract irritation, and mental confusion. It may also lead to the formation of methemoglobin ultimately causing cyanosis. Young infants and patients that have a deficiency of glucose-6-phosphate dehydrogenase can cause hemolytic anemia and hemolysis. Hypersensitivity reactions including generalized urticaria, anaphylaxis, tachycardia, hypotension, and bronchospasm have been reported at the site of injection.
What are the Trade Names of Methylene Blue?
Methylene blue is traded in the market with a variety of names like desmoid Piller, Pantone, desmoid pillen, vitableu, and urolene blue. Methylene blue has many synonym names as well like methylthionine chloride, tetra methylthionine chloride, methylthioninium chloride, Aizen methylene blue, and swiss blue.
Fun Facts
It is slightly irritant to the eyes.
It can cause redness in the eyes tissues if it gets in contact with the eyes.
If you are having a deficiency of glucose-6-phosphate dehydrogenase, then you should not be treated with methylene blue.
Symptoms of overdose of Methylene blue are Abdominal or stomach pain, bigger, dilated, or enlarged pupils, dark urine, difficulty breathing, fever, headache, increased sensitivity of the eyes to light, nausea, pale skin, blue staining of the urine, skin, and mucous membranes, rapid heart rate, rapid shallow breathing, etc.
FAQs on Methylene Blue Chemical Structure Properties and Applications
1. What is methylene blue in chemistry?
Methylene blue is a heterocyclic aromatic organic dye with the molecular formula C16H18ClN3S that acts as a redox indicator and biological stain. It belongs to the thiazine dyes family and appears as a dark green solid that forms a deep blue solution in water. In chemistry, it is widely used as:
- A redox indicator in oxidation–reduction reactions
- A staining agent in microbiology and histology
- A model compound in photochemistry and analytical chemistry
2. What is the chemical formula and molar mass of methylene blue?
The chemical formula of methylene blue (chloride salt) is C16H18ClN3S, and its molar mass is approximately 319.85 g·mol-1. Structurally, it contains:
- A phenothiazine core
- Two dimethylamino (–N(CH3)2) groups
- A positively charged nitrogen center balanced by Cl-
3. Why is methylene blue used as a redox indicator?
Methylene blue is used as a redox indicator because it changes color depending on its oxidation state. In its oxidized form, it is blue, and when reduced to leucomethylene blue, it becomes colorless. This reversible change occurs due to gain or loss of electrons:
- Oxidized form: Blue (electron-deficient)
- Reduced form: Colorless (electron-rich)
4. What type of compound is methylene blue?
Methylene blue is a cationic thiazine dye and a heterocyclic aromatic compound. It contains:
- A sulfur and nitrogen-containing heterocyclic ring
- Conjugated double bonds responsible for strong light absorption
- A permanent positive charge on nitrogen
5. How does methylene blue change color in the blue bottle experiment?
In the blue bottle experiment, methylene blue turns blue when oxidized by oxygen and becomes colorless when reduced by glucose in alkaline solution. The process involves:
- Glucose reducing methylene blue to leucomethylene blue (colorless)
- Dissolved O2 reoxidizing it back to the blue oxidized form
6. Is methylene blue an acid or a base?
Methylene blue behaves as a basic dye because it carries a positively charged nitrogen ion in solution. It is not a strong Brønsted acid or base but forms cations that bind to negatively charged species. Key points include:
- Exists as a cation (MB+) in water
- Forms salts with anions like Cl-
- Binds strongly to negatively charged cell components
7. Why is methylene blue blue in color?
Methylene blue appears blue because its conjugated π-electron system absorbs light in the red region of the visible spectrum. Due to its extended conjugation:
- It absorbs wavelengths around 660 nm (red light)
- The complementary color observed is blue
8. What are the common uses of methylene blue in chemistry and industry?
Methylene blue is widely used as a laboratory indicator, stain, and redox mediator. Its common applications include:
- Redox titrations and kinetic studies
- Biological staining of cells and bacteria
- Analytical chemistry for detecting reducing agents
- Textile and paper dyeing processes
9. What is the difference between methylene blue and leucomethylene blue?
The main difference is that methylene blue is the oxidized blue form, while leucomethylene blue is the reduced colorless form. The distinction is based on electron transfer:
- Methylene blue (MB+): Oxidized, blue, electron-deficient
- Leucomethylene blue: Reduced, colorless, electron-rich
10. Is methylene blue soluble in water?
Yes, methylene blue is highly soluble in water because it exists as a positively charged ionic compound. Its solubility is due to:
- Electrostatic interaction between MB+ and water molecules
- Hydration of the chloride counterion (Cl-)
- Polar functional groups in its structure
