| 摘要 |
Para-nitrobenzoic acid is prepared by the oxidation of para-nitrotoluene which may be alone or in admixture with its ortho- and metaisomers, with a gas consisting of or containing free oxygen in the presence of up to 60 per cent nitric acid. The molar ratio of nitric acid (based on 100 per cent nitric acid) to p-nitrotoluene may vary from 1 to 10. Any pressure above the vapour pressure of water at the prevailing temperature is suitable for the reaction. The preferred temperature range is 140-210 DEG C., and the preferred oxygen containing gas is air, although pure oxygen, as well as any oxygen-containing mixture of gases may be used so long as the other components are inert with respect to the reaction. It is preferable to introduce large quantities of oxygen at a fast rate at the beginning of the reaction and to decrease the rate towards the end of the reaction. The reaction may be carried out batchwise or continuously. At the end of the reaction the unreacted nitrotoluene may be distilled from the reaction mass and water introduced to replace that lost during distillation. The distillation residue may then be filtered and the filtrate boiled with water, cooled, filtered and dried to give the pure para-nitrobenzoic acid. Examples are given.
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