Phenols and Nitro Groups
Iron (III) Chloride Test for
Chloride - Pyridine Test for Water-Insoluble Phenols
Iron (II) Hydroxide Test for
Iron (III) Chloride Test for Water-Soluble Phenols
Procedure (for water-soluble phenols)
The iron (III) chloride test for phenols is not completely reliable for acidic
phenols, but can be administered by dissolving 15 mg of the unknown compound
in 0.5 mL of water or water-alcohol mixture and add 1 to 2 drops of 1% aqueous
iron (III) chloride solution.
A red, blue, green, or purple color is a positive test.
Since the quantity of material is extremely small, the test solution can be
diluted with water and flushed down the drain.
- Pyridine Test for Water-Insoluble Phenols
Procedure (for water-insoluble phenols or less
A more sensitive test for phenols consists of dissolving or suspending 15 mg
of the unknown in 0.5 mL of methylene chloride and adding 3-5 drops of a 1%
solution ferric chloride in methylene chloride. Add a drop of pyridine and
Positive Test (b)
Addition of pyridine and stirring will produce a color if phenols or enols
(II) Hydroxide Test for Nitro Groups
Add about 10 mg of the compound to 1 mL of the ferrous ammonium sulfate reagent
in a test tube, and then add 0.7 mL of the 2N alcoholic potassium
hydroxide reagent. Stopper the tube, and shake. Note the color of the precipitate
after 1 minute.
Ferrous Ammonium Sulfate Reagent: To 50 mL of recently boiled,
distilled water add 2.5 g of ferrous ammonium sulfate crystals and 0.2
mL of concentrated sulfuric acid.
The Alcoholic Potassium Hydroxide Reagent will already be prepared for you.
A positive test is the formation of the red-brown precipitate of iron(III)
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 compounds
give a positive test in 30 seconds. The speed with which the nitro compound
is reduced depends on its solubility.
Pour solutions into the appropriate waste container.