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Methyl red

Methyl red
Skeletal formula of methyl red
Ball-and-stick model of methyl red
Crystals of Methyl red sodium salt.jpg
Names
Preferred IUPAC name
2-{[4-(Dimethylamino)phenyl]diazenyl}benzoic acid
Identifiers
3D model (Jmol)
ChEBI
ChemSpider
ECHA InfoCard 100.007.070
KEGG
PubChem CID
Properties
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
Harmful Xn
R-phrases R20, R21, R22, R36/37/38, R40
S-phrases S24/25
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
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 pKa 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:

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).

The MR test, the "M" portion of the four IMViC tests, is used to identify enteric bacteria based on their pattern of glucose metabolism. All enterics initially produce pyruvic acid from glucose metabolism. Some enterics subsequently use the mixed acid pathway to metabolize pyruvic acid to other acids, such as lactic, acetic, and formic acids. These bacteria are called methyl-red positive and include Escherichia coli and Proteus vulgaris. Other enterics subsequently use the butylene glycol pathway to metabolize pyruvic acid to neutral end products. These bacteria are called methyl-red-negative and include Serratia marcescens and Enterobacter aerogenes.


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Wikipedia

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