Methylene Blue Preparation, Properties, and Practical Applications
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
(Image will be Uploaded Soon)
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.
(Image will be Uploaded Soon)
Preparation of Methylene Blue
Methylene blue is prepared by the oxidation of dimethyl-4-phenylenediamine in the presence of sodium thiosulfate.
(Image will be Uploaded Soon)
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: Complete Guide for Chemistry Students
1. What is methylene blue and what is its chemical formula?
Methylene blue is a synthetic basic dye belonging to the thiazine class of compounds. It is a heterocyclic aromatic chemical compound with the chemical formula C₁₆H₁₈ClN₃S. In its solid state, it appears as dark green, odourless crystals, but it dissolves in water to form a characteristic deep blue solution. It is widely recognised for its use as a stain in biology and as an indicator in chemistry.
2. What are the key physical and chemical properties of methylene blue?
Methylene blue exhibits several distinct properties relevant to students of chemistry.
- Appearance: It is a solid in the form of dark green crystals or powder.
- Colour in Solution: Forms a deep blue solution when dissolved in water.
- Solubility: It is soluble in water, ethanol, and chloroform but insoluble in non-polar solvents like ether.
- Melting Point: It has a melting point range of 100-110 °C, at which it also undergoes decomposition.
- Molecular Weight: The molar mass of methylene blue is approximately 319.85 g/mol.
- Stability: It is stable under recommended storage conditions, away from strong oxidising agents.
3. What are the main uses of methylene blue in chemistry and medicine?
Methylene blue has a diverse range of applications across different scientific fields.
- In Chemistry: It is primarily used as a redox indicator in analytical chemistry, famously demonstrated in the 'blue bottle experiment'. Its colour changes in response to oxidising or reducing conditions.
- In Biology: It serves as a vital bacteriological stain, helping to visualise cell nuclei and parasites under a microscope.
- In Medicine: It is an antidote for cyanide poisoning and is used to treat methemoglobinemia, a blood disorder where haemoglobin cannot effectively release oxygen to body tissues. It also has antimalarial and antiseptic properties.
4. How does methylene blue function as a redox indicator?
Methylene blue functions as a redox indicator because it can exist in two distinct forms with different colours. Its oxidized form is deep blue, while its reduced form, known as leucomethylene blue, is colourless. In a chemical reaction, methylene blue acts as an electron acceptor. When it accepts electrons (is reduced), its complex conjugated system is broken, causing it to lose its colour. When it loses electrons (is oxidized), the conjugation is restored, and the blue colour reappears. This reversible colour change occurs at a specific electrode potential, making it ideal for signalling the endpoint of a redox titration.
5. What is the basic chemical structure of methylene blue?
The chemical structure of methylene blue is based on a central, three-ring phenothiazine skeleton. The central ring is a thiazine ring, which contains both a sulphur and a nitrogen atom. This core is flanked by two benzene rings. Two dimethylamino groups (—N(CH₃)₂) are attached as substituents to these outer rings. The positive charge of the molecule is typically located on the sulphur atom, and it exists as a salt, most commonly with a chloride ion (Cl⁻).
6. Why does methylene blue have such an intense colour?
The intense blue colour of methylene blue is a direct result of its molecular structure. The molecule contains a large, extended system of conjugated double bonds (alternating single and double bonds) that spans across its three-ring structure. This extensive conjugation allows the molecule to absorb light in the orange-red portion of the visible spectrum (around 665 nm). Because it absorbs orange-red light, the light it reflects and transmits appears as its complementary colour, which is a deep blue.
7. How is a standard laboratory solution of methylene blue prepared from its powder form?
Preparing a methylene blue solution is a common procedure in a chemistry lab. To prepare a standard solution, such as a 0.1% (w/v) solution, you would:
- Carefully weigh out 0.1 grams of methylene blue powder using an analytical balance.
- Dissolve the powder in a small amount of distilled water in a beaker.
- Transfer the dissolved solution into a 100 mL volumetric flask.
- Carefully add more distilled water to the flask until the bottom of the meniscus reaches the 100 mL calibration mark.
- Stopper the flask and invert it several times to ensure the solution is homogeneous.
8. What is the difference between methylene blue and its reduced form, leucomethylene blue?
The primary difference lies in their oxidation state and, consequently, their colour.
- Methylene Blue is the oxidized form of the compound. It has an extensive conjugated pi-system, which allows it to absorb visible light and appear intensely blue.
- Leucomethylene Blue is the reduced form, created when methylene blue accepts two electrons and a proton. This reduction process breaks the conjugation in the molecule's core structure. As a result, it can no longer absorb light in the visible spectrum and is therefore colourless.
9. What are the potential health risks or side effects associated with using methylene blue?
While medically useful, methylene blue is a biologically active substance and can cause side effects. Common effects include turning the urine or stool a blue-green colour. Other possible side effects at therapeutic doses can include nausea, vomiting, headache, and dizziness. Inappropriately high doses can be dangerous, potentially causing serious conditions like serotonin syndrome (if mixed with certain antidepressants), high blood pressure, chest pain, confusion, and even inducing methemoglobinemia—the very condition it is used to treat at lower doses.
