Place about 0.1 g or 0.1 mL of the compound in a 16 × 150 mm test tube. Carefully add, by means of a pipet, 1 mL of glacial acetic acid and 1 mL of 57% hydroiodic acid (sp gr 1.7). Add a boiling chip, and insert into the mouth of the test tube a gauze plug as described below. The gauze plug is twisted so as to make a good fit and pushed down so that it is 4 cm from the mouth of the test tube. A small piece of nonabsorbent cotton is gently pushed on top of the plug by means of a glass rod so as to make a disk of cotton 2-3 mm thick. A piece of filter paper 2 × 10 cm is folded longitudinally, moistened with a solution of mercuric nitrate, and placed on the cotton disk. The test tube is immersed to a depth of 4-5 cm in an oil bath kept at 120-130°C. Do this reaction in the hood. When the reaction mixture boils, vapors rise through the porous plug, which usually turns gray. The volatile alkyl halide, rising through the plugs, reacts with the mercuric nitrate to produce a light orange or vermilion color due to the formation of the mercuric iodide.
Gauze Plugs: A solution of 0.10 g of lead acetate in 1.0 mL of water is added to 6.0 mL of 1 M sodium hydroxide solution and stirred until the precipitate dissolves. To this solution is added a solution of 0.5 g of hydrated sodium thiosulfate in 1.0 mL of water. About 0.5 mL of glycerol is added, and the solution is diluted to 10.0 mL. About 5 mL of this solution is pipetted on strips of double cheesecloth 2 ~ 45 cm. The strips of cloth are dried and rolled to fit the test tube.
Mercuric Nitrate Solution: A saturated solution of mercuric nitrate is prepared in 24.5 mL of distilled water to which has been added 0.5 mL of concentrated nitric acid. Mercury compounds are very toxic and require handling with special care.
Formation of an orange or vermilion color on the test paper within a 10-min heating period is a positive test. A yellow color constitutes a negative or doubtful test.
Some alcohols (butyl or lower) give a positive test.
Sulfur-containing functional groups liberate hydrogen sulfie which interferes with the test.
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