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Methyl Red

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Methyl Red Basic information
Methyl Red Chemical Properties
  • Melting point:179-182 °C (lit.)
  • Boiling point:412.44°C (rough estimate)
  • Density 0.839 g/mL at 25 °C
  • vapor density 9.3 (vs air)
  • refractive index 1.5930 (estimate)
  • Flash point:11 °C
  • storage temp. Store at +5°C to +30°C.
  • solubility ethanol: soluble1mg/mL
  • form Solid
  • pka4.95(at 25℃)
  • Colour Index 13020
  • color Reddish-violet
  • PH Range4.4(red)-6.3(yellow)
  • OdorOdorless
  • Water Solubility Practically insoluble in water. Soluble in alcohol, acetic acidSoluble in ethanol. Insoluble in water.
  • λmax410nm, 530nm, 427nm, 519nm
  • Merck 14,6119
  • BRN 750102
  • Stability:Stable. Incompatible with strong oxidizing agents.
  • Major ApplicationWaveguides, LED sensors, photoresists, liquid crystals, sol-gel matrix, optical sensors, paints, toys, detection of thiols, food freshness sensors, dental product, saliva sampling method, detecting lactic acid, carbohydrates
  • CAS DataBase Reference493-52-7
  • NIST Chemistry ReferenceBenzoic acid, 2-[[4-(dimethylamino)phenyl]azo]-(493-52-7)
  • IARC3 (Vol. 8, Sup 7) 1987
  • EPA Substance Registry SystemMethyl red (493-52-7)
Safety Information
Methyl Red Usage And Synthesis
  • DescriptionMethyl red is a commonly used indicator for acid-base titrations. This chemical is usually yellow but turns red below pH 4.0. Bacteria exhibiting mixed acids fermentation will accumulate acids in the medium, resulting in a color change. Approximately five drops of methyl red reagent are added to an overnight culture grown in MRVP broth to determine the test result.
    Different bacteria convert dextrose and glucose to pyruvate using different metabolic pathways. Some of these pathways produce unstable acidic products which quickly convert to neutral compounds. Some organisms use the butylene glycol pathway, which produces neutral end products, including acetoin and 2,3-butanediol. Other organisms use the mixed acid pathway, which produces acidic end products such as lactic, acetic, and formic acid. These acidic end products are stable and will remain acidic.
    The Methyl Red test involves adding the pH indicator methyl red to an inoculated tube of MR-VP broth. If the organism uses the mixed acid fermentation pathway and produces stable acidic end-products, the acids will overcome the buffers in the medium and produce an acidic environment in the medium. When methyl red is added, if acidic end products are present, the methyl red will stay red.
  • Chemical Propertiesdark red crystalline powder
  • UsesUsed as pH indicator.
  • UsesAs indicator in 0.1% alcoholic solution; pH: 4.4 red, 6.2 yellow. Used for titrating NH3, weak organic bases, e.g., alkaloids; not suitable for organic acids, except oxalic and picric acid. Methyl red is easily reduced, thereby losing its color, and readings should be made promptly. It is gradually being replaced by sulfonphthalein indicators, such as bromcresol green, which are more stable and exhibit a sharper change in color.
  • DefinitionChEBI: An azo dye consisting of benzoic acid substituted at position 2 by a 4-[(dimethylamino)phenyl]diazenyl group.
  • DefinitionAn acid–base indicator that is red in solutions below a pH of 4.2 and yellow above a pH of 6.3. It is often used for the same types of titration as methyl orange but the transition range of methyl red is nearer neutral (pH7) than that of methyl orange. The two molecules are structurally similar.
  • Definitionmethyl red: An organic dye similarin structure and use to methyl orange.It changes from red below pH4.4 to yellow above pH 6.0 (at 25°C).
  • Preparation2-Aminobenzoic acid?diazo, and N,N-dimethylaniline coupling.
  • HazardQuestionable carcinogen.
  • Safety ProfileQuestionable carcinogen with experimental tumorigenic data. Mutation data reported. When heated to decomposition it emits toxic fumes of NOx.
  • Properties and Applicationsmoderate soluble in ethanol, insoluble in water. Alcohol solution to join hydrochloric acid for purple; Add sodium hydroxide to dim yellow.
  • Purification MethodsThe acid is extracted with boiling toluene using a Soxhlet apparatus. The crystals which separate on slow cooling to room temperature are filtered off, washed with a little toluene and recrystallised from glacial acetic acid, *benzene or toluene followed by pyridine/water. Alternatively, dissolve it in aqueous 5% NaHCO3 solution, and precipitate it from a hot solution by dropwise addition of aqueous HCl. Repeat this until the extinction coefficients do not increase. [Beilstein 16 IV 504.]
Methyl Red Preparation Products And Raw materials
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