Preparation method of p-chlorotoluene
It is derived from p-toluidine through diazotization and replacement. Add p-toluidine and hydrochloric acid into the reaction pot and stir and heat, and after dissolving at 60°C, cool to below 15°C, and add sodium nitrite solution dropwise. After reaching the end, continue to stir for 0.5h. Add cuprous chloride hydrochloric acid solution and stir at room temperature for 3h. Then it was heated to 60°C for 0.5h, cooled to room temperature and left to stand for separation, discarded the acid water layer, washed with water to neutrality, filtered to obtain p-chlorotoluene. The cuprous chloride used in the reaction can be prepared as follows: add copper sulfate and sodium chloride to water, stir and heat to 40°C to dissolve, add liquid caustic soda and sodium metabisulfite solution to precipitate the precipitate, stand for layering, and separate the upper layer The waste liquid, the precipitate is soaked and washed with water, and dissolved in hydrochloric acid to obtain a cuprous chloride hydrochloric acid solution. Raw material consumption quota: p-toluene (95%) 897kg/t, sodium nitrite 533kg/t, hydrochloric acid 2435kg/t. To
From toluene for aromatic ring chlorination. The preparation methods are as follows.
Diazotization method
Add industrial hydrochloric acid and p-toluidine into the reaction kettle. The temperature in the kettle is reduced to 0°C to make p-toluidine generate hydrochloride. Stir and add sodium nitrite solution to cause diazotization reaction. The temperature is maintained. At 0～5℃ for about 30min, after the diazotization reaction is completed, add it to the stirred cuprous chloride solution, gradually warm to room temperature, stir at room temperature for 2.5～3h, and then heat to 60℃. The reactants are gradually decomposed into nitrogen and p-chlorotoluene, and then steam distilled. The mixture of p-chlorotoluene and water is collected and stratified. The organic layer is washed with acid, then washed with water, dried, and distilled to collect at 158～162℃. The distillate is p-chlorotoluene, and the yield is about 70% to 79%.
Direct chlorination method
The toluene dried and dehydrated by salt is measured in the metering tank and then enters the toluene chlorination reactor. The metered chlorine is introduced from the bottom of the reactor. Toluene and chlorine are at a certain temperature, and ferric chloride is used as a catalyst for benzene ring chlorination. , To produce a chlorotoluene chlorination solution, the chlorination solution is used to drive off the residual gas and hydrogen chloride with nitrogen, and then crudely steamed to obtain a mixture of p-chlorotoluene and o-chlorotoluene. But different, the general pair-to-neighbor ratio is 55:45. The separation of p-chlorotoluene and o-chlorotoluene can be carried out by distillation method, molecular sieve adsorption method, distillation and crystallization combined method, etc. The combined method of distillation and crystallization has low energy consumption, and the content of p-chlorotoluene and o-chlorotoluene are higher. If the falling film freezing crystallization method is adopted, the content of p-chlorotoluene can reach more than 99%.