Dinitrophenylhydrazine Test for Aldehydes and Ketones

Concentrated sulfuric acid may produce severe chemical burns, and 2,4-dinitro-phenylhydrazine is a possible mutagen and may cause skin sensitization. Wear latex gloves when preparing and handling solutions involving these reagents. If this acid or the ethanolic solution of 2,4-dinitrophenylhydrazine comes in contact with your skin, immediately flood the affected area with water and rinse it with 5% sodium bicarbonate solution. 

Preparation Sign in at www.cengage.com/login to read the MSDSs for the chemicals used or produced in this procedure. 

If the test reagent is not supplied, prepare it by dissolving 0.2 g of 2,4-dinitro-phenylhydrazine in 1 mL of concentrated sulfuric acid. Add this solution, with stirring. to 1.5 mL of water and 5 mL of 95% ethanol. Stir the solution vigorously and then filter it to remove any undissolved solids. 

Dissolve 1 or 2 drops of a liquid, or about 100 mg of a solid, in 2 mL of 95% ethanol, and add this solution to 2 mL of the 2.4-dinitrophenylhydrazine reagent. Shake the mixture vigorously if a precipitate does not form immediately, let the solution stand for 15 min. 

If more crystals are desired for a melting-point determination, dissolve 200-500 mg of the carbonyl compound in 20 mL of 95% ethanol, and add this solution to 15 mL of the reagent. Recrystallize the product from aqueous ethanol. 

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Chemical Tests. The 2,4-dinitrophenylhydrazine test for aldehydes and ketones (see Chapter 9) may be done to confirm the presence of the carbonyl group. The isolation of this derivative and the determination of its melting point (Lit. value = 283 °C) would aid in establishing the identity of the product. 

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