Chemical Structure of Methyl Red

What is Methyl Red?

Methyl Red is a synthetic azo dye consisting of benzoic acid substituted at position 2 by a 4-[(dimethylamino)phenyl]diazenyl group. It is also called as C.I. Acid Red 2. It is often used in laboratory settings and chemical analysis as a pH indicator to visually indicate the pH of a solution through a color change.

Macsen Laboratories is the leading manufacturer and supplier of Methyl Red dye with ISO certification.
Name of Product Methyl Red
IUPAC Name 2-[[4-(dimethylamino)phenyl]diazenyl]benzoic acid
Synonyms C.I. Acid Red 2; 2-Carboxy-4'-(dimethylamino)azobenzene; Cerven methylova; 2-(N,N-dimethyl-4-aminophenyl) azobenzenecarboxylic acid
CAS No 493-52-7
Molecular Formula C15H15N3O2
Molecular Weight 269.30 g/mol
Pubchem CID 10303


SR. No Criteria Limit/Specification
1 Appearance (form) Crystalline Powder
2 Appearance (color) Dark Red to Maroon to Violet
3 Odor Odorless
4 Solubility Insoluble in Water
Soluble in Ethanol, Chloroform & Acetic Acid
5 Melting Point 179–182 °C
6 Density 0.791 g/cm3
7 UV-vis (λmax) 410 nm (yellow form)
8 Loss on Drying (at 110°C) NMT 5.0 %


  • Methyl red is primarily used as a pH indicator in titrations and other chemical tests to determine the pH of a solution. It undergoes a color change from red (at pH under 4.4, acidic) to yellow (at pH over 6.2, slightly alkaline) and orange in between.
  • In microbiology, methyl red is used in the methyl red test (MR test), which is used to identify and differentiate between certain bacterial species, particularly those belonging to the Enterobacteriaceae family such as Escherichia coli and Proteus vulgaris.
  • It can be used in various chemical analysis to monitor pH changes during reactions.
  • Methyl Red, along with murexide, is being researched for its possible use in the sonochemical destruction of contaminants including chlorinated hydrocarbons.


Q. How to prepare Methyl red Indicator ?

A 1% solution of Methyl red indicator is generally used for titration. It can be prepared by dissolving 1g of Methyl red powder in 500 ml of ethanol and then diluting it to 1000 ml with distilled water.

Q. Is Methyl red soluble in water ?

Methyl red is insoluble in water but is soluble in organic solvents.

Q. Is Methyl red an acid or base?

Methyl red is a weak acid.

Q. Is Methyl Red carcinogenic?

The International Agency for Research on Cancer places methyl red in group 3, which is unclassified with regard to its potential to cause cancer in humans.

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