Methyl red

Methyl red
Names
	Preferred IUPAC name 2-{[4-(Dimethylamino)phenyl]diazenyl}; benzoic acid
Identifiers
CAS Number	493-52-7 (free base) ; 63451-28-5 (HCl salt) ; 845-10-3 (sodium salt) ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:49770 ;
ChemSpider	9881 ;
ECHA InfoCard	100.007.070
EC Number	207-776-1;
KEGG	C19459 ;
PubChem CID	10303;
RTECS number	DG8960000;
UNII	69083AX1ZX (free base) ; RFA0W63690 (HCl salt) ; 311GZ0QHWN (sodium salt) ;
CompTox Dashboard (EPA)	DTXSID90859408 DTXSID1042154, DTXSID90859408 ;
	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+ Key: CEQFOVLGLXCDCX-WUKNDPDISA-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	269.304 g·mol−1
Density	0.791 g/cm3
Melting point	179–182 °C (354–360 °F; 452–455 K)
Solubility	soluble in ethanol
Acidity (pKa)	5.1
UV-vis (λmax)	410 nm (yellow form)
Hazards
	GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H351, H411
Precautionary statements	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). verify (what is ?) Infobox references

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 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.