Acid orange 19 is an azo dye that is used to color polyamide and wool fibers. It is usually available as a fine reddish-orange powder. The dye is soluble in water, producing an orange solution. When this solution is treated with concentrated hydrochloric acid, it turns red. Acid orange 19 is prepared by azo coupling with 1-Hydroxynaphthalene-4-sulfonic acid. Like most azo dyes, it is mildly toxic when orally ingested and has carcinogenic properties.
References