Acid orange 5

Acid orange 5

Names
IUPAC name Sodium 4-[(E)-(4-anilinophenyl)diazenyl]benzenesulfonate
Other names Fast yellow; Tropaeolin OO
Identifiers
CAS Number	554-73-4
3D model (JSmol)	Interactive image
ChemSpider	10660
ECHA InfoCard	100.008.248
PubChem CID	11133
CompTox Dashboard (EPA)	DTXSID8060294
InChI InChI=1S/C18H15N3O3S.Na/c22-25(23,24)18-12-10-17(11-13-18)21-20-16-8-6-15(7-9-16)19-14-4-2-1-3-5-14;/h1-13,19H,(H,22,23,24);/q;+1/p-1/b21-20+; Key: MLVYOYVMOZFHIU-ANVLNOONSA-M InChI=1/C18H15N3O3S.Na/c22-25(23,24)18-12-10-17(11-13-18)21-20-16-8-6-15(7-9-16)19-14-4-2-1-3-5-14;/h1-13,19H,(H,22,23,24);/q;+1/p-1/b21-20+; Key: MLVYOYVMOZFHIU-LGLICYIRBD
SMILES c1ccc(cc1)Nc2ccc(cc2)/N=N/c3ccc(cc3)S(=O)(=O)[O-].[Na+]
Properties
Chemical formula	C18H14N3NaO3S
Molar mass	375.38 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Tropaeolin OO (pH indicator)
below pH 1.4		above pH 3.2
1.4	⇌	3.2

Acid orange 5 is a compound with formula Na(C₆H₅NHC₆H₄N=NC₆H₄SO₃). It is an azo dye. It is also used as a pH indicator; it is red in pH under 1.4, orange-yellow in pH over 3.2.