Acid orange 5

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.^[1]

Preparation

Acid orange 5 may be prepared by diazotization of sulfanilic acid, followed by reaction with diphenylamine:

HO₃SC₆H₄N₂+ + (C₆H₅)₂NH → HO₃SC₆H₄N\dNC₆H₄N(H)C₆H₅ + H+

References

1. ^ Beilstein 16 II 171.