Methyl red

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.

Methyl red
Names
Preferred IUPAC name
2-{[4-(Dimethylamino)phenyl]diazenyl}benzoic acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.007.070
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)
Solubility soluble in ethanol
UV-vismax) 410 nm (yellow form)
Hazards
GHS labelling:
Warning
H351, H411
P201, P202, P273, P281, P308+P313, P391, P405, P501
NFPA 704 (fire diamond)
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 YN ?)
Infobox references
Methyl Red (pH indicator)
below pH 4.4 above pH 6.2
4.4 6.2
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