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Narrative
Dilute hydrochloric acid is added to a test tube containing aqueous acetaminophen and a second test tube containing water as a control. An aqueous solution of sodium nitrite is added to each test tube. Next a solution of sulfamic acid is added. Upon addition of sodium hydroxide, an orange solution is produced with acetaminophen but not in the control. This reaction is used for the clinical determination of the analgesic acetaminophen in human serum.

Discussion
Phenols and tertiary amines react with nitrous acid to undergo ring nitrosation. With phenols, the nitroso group is air oxidized to a nitro group.