Add about 10 mg of the compound to 1 mL of the ferrous sulfate reagent in a test tube, and then add 0.7 mL of the alcoholic potassium hydroxide reagent. Insert a glass tube so that it reaches the bottom of the test tube, and pass a stream of inert gas through the tube for about 30 sec in order to remove air. Stopper the tube quickly, and shake. Note the color of the precipitate after 1 min.
Ferrous Sulfate Reagent: To 100 mL of recently boiled, distilled water add 5.0 g of ferrous ammonium sulfate crystals and 0.4 mL of concentrated sulfuric acid. An iron nail is introduced to retard air oxidation.
Alcoholic Potassium Hydroxide Reagent: Three grams of potassium hydroxide is dissolved in 3 mL of distilled water, and this solution is added to 100 mL of 95% ethanol.
A positive test is the formation of the red-brown to brown precipitate of iron(III) hydroxide.
The red-brown to brown precipitate of iron(III) hydroxide (ferric hydroxide) is formed by the oxidation of iron(II) hydroxide (ferrous hydroxide) by the nitro compound, which in turn is reduced to the primary amine. A negative test is indicated by a greenish precipitate. In some cases partial oxidation may cause a darkening of the ferrous hydroxide. Practically all nitro compound give a positive test in 30 sec. The speed with which the nitro compound is reduced depends on its solubility.
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