To a solution of
26.6 g. (0.66 mole) of sodium hydroxide in 240 cc. of water is added
80 g. (0.416 mole) of 4-nitrophthalimide (p. 459) (Note
1). The mixture is heated rapidly to boiling and boiled gently for ten minutes. The solution is made barely acid to litmus with concentrated
nitric acid (sp. gr. 1.42); after the neutral point is reached, an additional
70 cc. (100 g., 1.1 moles) of nitric acid is added (Note
2). The solution is again boiled for three minutes, then cooled below room temperature, transferred to a
1-l. separatory funnel, and extracted with two
300-cc. portions of alcohol-free ether (Note
3). Care is taken to ensure thorough mixing before separation of the layers. After the extract is dried over anhydrous
sodium sulfate, the
ether is distilled until solid begins to separate. The concentrated
ether solution is poured into a
porcelain dish and the residual solvent allowed to evaporate in a
hood (Note
4). The practically white crystals of
4-nitrophthalic acid which separate melt at
163–164° and have a neutralization equivalent of 105.5 (theoretical, 105.5). The yield is
85–87 g. (
96–99 per cent of the theoretical quantity).