This test must be done in a hood. Place 0.5 mL of 20% fuming sulfuric acid (hazardous) in a clean, dry test tube, and add 0.25 mL or 0.25 g of the unknown. Shake the mixture vigorously, and allow it to stand for a few minutes.
A positive test for the presence of an aromatic ring is complete dissolution of the unknown, evolution of heat, and minimal charring.
Caution: Use this reagent with relatively inert compounds only, such as those compounds that do not dissolve in the solubility tests with concentrated sulfuric acid. Compounds for which preliminary tests indicate strongly activating groups (OH, NH2, etc.) may be decomposed violently by fuming sulfuric acid.
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