MR test

Methyl red

Names
Preferred IUPAC name 2-{[4-(Dimethylamino)phenyl]diazenyl}benzoic acid
Identifiers
CAS Number	493-52-7 Y 63451-28-5 (HCl salt) N 845-10-3 (sodium salt) N
3D model (JSmol)	Interactive image
ChEBI	CHEBI:49770 N
ChemSpider	9881 N
ECHA InfoCard	100.007.070
KEGG	C19459 Y
PubChem CID	10303
InChI InChI=1S/C15H15N3O2/c1-18(2)12-9-7-11(8-10-12)16-17-14-6-4-3-5-13(14)15(19)20/h3-10H,1-2H3,(H,19,20)/b17-16+ N Key: CEQFOVLGLXCDCX-WUKNDPDISA-N N InChI=1/C15H15N3O2/c1-18(2)12-9-7-11(8-10-12)16-17-14-6-4-3-5-13(14)15(19)20/h3-10H,1-2H3,(H,19,20)/b17-16+ Key: CEQFOVLGLXCDCX-WUKNDPDIBD
SMILES CN(C)c2ccc(/N=N/c1ccccc1C(O)=O)cc2
Properties
Chemical formula	C15H15N3O2
Molar mass	269.30 g·mol−1
Density	0.791 g/cm3
Melting point	179–182 °C (354–360 °F; 452–455 K)
Solubility	soluble in ethanol
UV-vis (λmax)	410 nm
Hazards
EU classification (DSD) (outdated)	Xn
R-phrases (outdated)	R20, R21, R22, R36/37/38, R40
S-phrases (outdated)	S24/25
NFPA 704	1 2 0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Methyl red (2-(N,N-dimethyl-4-aminophenyl) azobenzenecarboxylic acid), also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions. It is an azo dye, and is a dark red crystalline powder. Methyl red is a pH indicator; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between, with a pK_a of 5.1.Murexide and methyl red are investigated as promising enhancers of sonochemical destruction of chlorinated hydrocarbon pollutants. Methyl red is classed by the IARC in group 3 - unclassified as to carcinogenic potential in humans.

As an azo dye, methyl red may be prepared by diazotization of anthranilic acid, followed by reaction with dimethylaniline:

Methyl red displays pH dependent , with protonation causing it to adopt a hydrazone/quinone structure.

Methyl Red have a special use in Histopathology for showing acidic nature of tissue and presence of organisms with acidic natured cell wall .

In microbiology, methyl red is used in the methyl red test (MR test), used to identify bacteria producing stable acids by mechanisms of mixed acid fermentation of glucose (cf. Voges–Proskauer test).