Methyl red

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Methyl red
Skeletal formula of methyl red
Ball-and-stick model of methyl red
Names
Preferred IUPAC name
2-{[4-(Dimethylamino)phenyl]diazenyl}
benzoic acid
Identifiers
3D model (
JSmol
)
ChEBI
ChemSpider
ECHA InfoCard
 100.007.070 Edit this at Wikidata
EC Number
  • 207-776-1
KEGG
RTECS number
  • DG8960000
UNII
  • 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
  • CN(C)c2ccc(/N=N/c1ccccc1C(O)=O)cc2
Properties
C15H15N3O2
Molar mass 269.304 g·mol−1
Density 0.791 g/cm3
Melting point 179–182 °C (354–360 °F; 452–455 K)[1]
Solubility soluble in ethanol[1]
UV-vis (λmax) 410 nm (yellow form)[1]
Hazards
GHS labelling:
GHS08: Health hazardGHS09: Environmental hazard
Warning
H351, H411
P201, P202, P273, P281, P308+P313, P391, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
1
0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)
Methyl Red (pH indicator)
below pH 4.4 above pH 6.2
4.4 ⇌ 6.2

Methyl red (2-(N,N-dimethyl-4-aminophenyl) azobenzenecarboxylic acid), also called C.I. Acid Red 2, is an

carcinogenic
potential in humans.

Color transition of methyl red solution under different acid–base conditions. Left: acidic, middle: about pH 5.1 (the pKa), right: alkaline

Preparation

As an azo dye, methyl red may be prepared by

diazotization of anthranilic acid, followed by reaction with dimethylaniline:[3]

Properties

The color of methyl red is pH dependent, because protonation causes it to adopt a hydrazone/quinone structure.

Methyl Red has a special use in histopathology for showing acidic nature of tissue and presence of organisms with acidic natured cell walls.

Methyl Red is detectably fluorescent in 1:1 water:methanol (pH 7.0), with an emission maximum at 375 nm (

UVB).[4]

Methyl red test

Methyl red test: Escherichia coli (left side) showing a 'positive' result, and Enterobacter cloacae (right side) showing a 'negative' result

In

Voges–Proskauer
test).

The MR test, the "M" portion of the four

Enterobacter aerogenes
.

Process

A tube filled with a glucose phosphate broth is inoculated with a sterile transfer loop. The tube is incubated at 35 °C (95 °F) for 2–5 days. After incubation, 2.5 ml of the medium are transferred to another tube. Five drops of the pH indicator methyl red is added to this tube. The tube is gently rolled between the palms to disperse the methyl red.

Expected results

Enterics that subsequently metabolize pyruvic acid to other acids lower the pH of the medium to 4.2. At this pH, methyl red turns red, a positive test. Enterics that subsequently metabolize pyruvic acid to neutral end products lower the pH of the medium to only 6.0. At this pH, methyl red is yellow, a negative test.

See also

References

  1. ^ a b c Sigma-Aldrich Co., Methyl red Archived 2015-12-09 at the Wayback Machine. Retrieved on 2014-06-02.
  2. ^ IB chemistry Higher Level: "IB Chemistry higher level notes: Indicators". Archived from the original on 2009-09-22. Retrieved 2009-11-29.
  3. ^ H. T. Clarke & W. R. Kirner (1941). "Methyl Red". Organic Syntheses; Collected Volumes, vol. 1, p. 374.
  4. ISSN 1226-1025
    .
  • "Microbiology, A Photographic Atlas for the Laboratory", Alexander, Street, Pearson Education, 2001.

External links

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