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.Beilstein 16 II 171.
Preparation Acid orange 5 may be prepared by diazotization of sulfanilic acid, followed by reaction with diphenylamine:
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