Acid orange 5
# Acid orange 5

Acid orange 5 is a compound with formula $Na(C_6H_5NHC_6H_4N=NC_6H_4SO_3).$ 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.

## Preparation

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

    $HO_3SC_6H_4N+2$ + $(C_6H_5)_2NH$ → $HO_3SC_6H_4N=NC_6H_4N(H)C_6H_5$ + $H^+$
