Synthesis 1*:
A wide-mouthed 250-cc. flask containing a mixture of 50 g. (0.25 mole) of technical 2,4-dinitrochlorobenzene and 18 g. (0.23 mole) of ammonium acetate is half immersed in an oil bath. The flask is fitted with a reflux condenser and an inlet tube, the lower end of which is at least 2 cm. wide (to prevent clogging) and which nearly touches the surface of the reaction mixture. During the operation ammonia gas is introduced through a bubble counter which contains a small amount of strong potassium hydroxide solution (12 g. of potassium hydroxide in 10 cc. of water).
The oil bath is heated to 170° and maintained at that temperature for six hours during which time ammonia gas is passed through at the rate of three to four bubbles per second. After the mixture has cooled, the solid is broken up by means of a glass rod and mixed with 100 cc. of water; the mixture is then heated to boiling and filtered while hot. The residue is dissolved in 500 cc. of boiling alcohol, and water is added (about 150 cc.) until the solution becomes turbid. Heat is applied until the turbidity disappears and then the solution is allowed to cool. After standing overnight, the crystals are filtered and dried. The yield is 31–35 g. (68–76 per cent of the theoretical amount) of 2,4-dinitroaniline, melting at 175–177° and. For further purification the product is recrystallized in the same manner from alcohol and water, using 20 cc. of alcohol per gram of solid. Ninety per cent of the crude material is recovered as recrystallized product melting sharply at 180°.
Synthesis 2:
Prepare a solution of 1 g of 2,2,4,4-tetranitrodiphenyl ether in 10 mL of dimethylformamide in a test tube and bubble gaseous ammonia through the solution for 15 minutes while maintaining a temperature of 25 C. The reaction is then poured into a beaker containing 50-75 mL of water. A precipitate of dinitroaniline will form. Allow several minutes for it to fully precipitate and to settle. Collect this material by filtering and allow it to dry. To the liquid filtrate add enough hydrochloric acid to make the solution slightly acidic to precipitate dinitrophenol, which can be collected by filtration and allowed to dry. Yield of dinitroaniline is 85%, yield of dinitrophenol is 65%.
An alternative to this process is to use only 0.5 g of 2,2,4,4-tetranitrodiphenyl ether in dimethylformamide and to use 0.28 g of 25% aqueous ammonia instead of gaseous ammonia. The mixture is sealed in a pressure reaction vessel and heated to 100 C for 15 minutes at a pressure of 4 to 5 atm. Yield of dinitroaniline is 90%, yield of dinitrophenol is 65%.
For more information on 2,4-dinitrophenol as well as an alternative synthesis please see its section here.
