One hundred sixty grams (1.7 moles) of a good grade of phenol and
80 g. (1.43 moles) of potassium hydroxide are placed in a
2-l. flask, and the mixture is heated to 130–140° until all the alkali has dissolved. The
potassium phenoxide is cooled to 100–110°, and
0.5 g. of copper catalyst (Note
1) and
78.8 g. (0.5 mole) of p-nitrochlorobenzene are added. The flask is then fitted with a
mechanical stirrer,
thermometer, and a
reflux condenser. The stirrer is started, and the contents of the flask are warmed with a
Bunsen burner to 150–160°, at which temperature a spontaneous reaction begins with ebullition and the separation of
potassium chloride. The flame should be removed during this stage of the reaction. Boiling nearly ceases within five to seven minutes, and another
78.8 g. (0.5 mole) of p-nitrochlorobenzene is added. The mixture is again heated as before until a second spontaneous reaction begins. This also proceeds for about five minutes without the application of heat. When boiling due to the exothermic reaction has ceased, heat is applied and a temperature of 150–160° is maintained for an additional thirty minutes. The dark-colored melt is then poured into 1.5 l. of ice water containing
50 g. of sodium hydroxide and stirred well to remove excess
phenol. The crude
p-nitrodiphenyl ether separates as a dark brown crystalline mass which is allowed to settle. The product is filtered on a
Büchner funnel, washed with 2 l. of water, and pressed as free from water as possible. After drying in the air it is distilled from a
500-cc. Claisen flask. The small fraction boiling up to 170°/8 mm., which contains
p-nitrochlorobenzene, is discarded. A fraction boiling at
170–188°/8 mm. and weighing
14 g. is collected (Note
2). The main fraction boiling at
188–193°/8 mm. boils at
188–190°/8 mm. on redistillation with no fore-run and practically no residue.
p-Nitrodiphenyl ether solidifies on cooling to diamond-shaped crystals melting at
56–58°. The yield is
173–177 g. (
80–82 per cent of the theoretical amount) (Note
3).