Methyl red

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]
Acidity (pKa) 5.1
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 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.[2] 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.

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