In a
3-l. three-necked flask equipped with a
mechanical stirrer and an inlet tube extending to the bottom of the flask is placed
2 l. of 30% methanolic potassium hydroxide (Note
1). The flask is immersed in an
ice bath, and, when the solution has cooled to 10°,
100 g. (0.73 mole) of p-nitrotoluene (Note
2) is added to the flask. Vigorous stirring is begun, and a rapid stream of air from a compressed-air source is passed through the inlet tube. After 3 hours the
ice bath is removed and the passage of air through the mixture is continued with uninterrupted, vigorous stirring for an additional 5 hours. The reaction mixture is immediately filtered with suction (Note
3), and the solid, while still on the filter, is washed with 2 l. of boiling water followed by
300 ml. of 95% ethanol at room temperature. The product is allowed to dry thoroughly in air and then is dissolved in a minimum quantity of boiling
benzene (Note
4). The hot solution is filtered to remove a small amount of insoluble red-orange material and is allowed to cool. The
p,p'-dinitrobibenzyl crystallizes as orange needles, m.p.
178–180°. The yield is
73–75 g. (
74–76%). A second recrystallization from
benzene gives yellow needles, m.p.
179–180°.