Dissolve 0.2 mL or 0.2 g of the unknown in 4 mL of 50% ethanol, and add 0.2 g of ammonium chloride and 0.2 g of zinc dust. Shake, and heat to boiling. Allow to stand for 5 min, filter, and test the action of the filtrate on Tollens reagent.
A positive test is the formation of a black or grey precipitate or a silver mirror.
This test depends on the reduction of the unknown to a hydrazine, a hydroxylmine, or an aminophenol; all these compounds are oxidized by Tollens reagent. This test cannot be applied if the original compound reduces Tollens reagent. Tertiary aliphatic compounds and aromatic nitro compounds give a positive test. Nitroso, azoxy, and azo compounds are reduced with zinc and ammonium chloride, with the products being oxidized in the Tollens test.
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