The synthetic routes of 2,6-dimethylaniline mainly include 2,6-dimethylphenol ammonolysis method, o-toluidine alkylation method, aniline methylation method, m-xylene double sulfonated nitration method and m-dimethylaniline method. Toluene nitration reduction method, etc.
Its preparation methods are as follows
(1) Using m-xylene as raw material, it is obtained by mixed acid nitration and catalytic hydrogenation. The process is to cool m-xylene to 0～5℃, add the cooled mixed acid (56.5% sulfuric acid, 28% nitric acid, 15.5% water) in batches, keep the temperature at 17℃～25℃ for the first time, add in 3h. Finished, the second time was added at 17-25°C in 2h, the final dropwise temperature was 25-30°C, the addition was completed within 1h, and then stirred at 25-30°C for 30min, the nitrates were separated and washed with water, and then reduced pressure The crude product was obtained by distillation, the fraction at 78-85°C/666.5Pa was distilled again, and 2,6-dimethylnitrobenzene was obtained by cooling and crystallization. 2,6-dimethylnitrobenzene is reduced, and iron powder and hydrochloric acid are used for stepwise reduction in the past, and iron powder is gradually added to 2,6-dimethylnitrobenzene and dilute hydrochloric acid solution, and then refluxed after adding 30min, cooling, then adding sodium carbonate to neutralize, adding water for distillation to obtain an oily solution, layering, and drying the oily layer to obtain a product. Catalytic hydrogenation has been used instead of iron powder reduction. In the presence of a catalyst, 2,6-dimethylnitrobenzene is subjected to catalytic hydrogenation to obtain a crude product, which is subjected to post-treatment to obtain a product. The products produced by this method are 2,6-dimethylaniline and 2,4-dimethylaniline, while the share of 2,6-dimethylaniline in the reaction process is small, which cannot meet the production requirements.
(2) Alkylation method, that is, using o-toluidine and methanol as raw materials, in the presence of a catalyst, the reaction is carried out under a certain pressure. In this reaction, in addition to the main product 2,6-dimethylaniline, there are many by-products, of which 2,3-dimethylaniline and 2,6-dimethylaniline have similar structures, similar physical properties, and boiling points. The difference is small and the separation is more difficult. Generally, the alkylated reactants are firstly separated from other by-products such as o-toluidine and tricolidine to obtain 2,3-dimethylaniline and 2,6-dimethylaniline with a content of 98%. The mixture of aniline, the mixture is the starting material (wherein the content of 2,3-dimethylaniline is 18%) through precision fractionation, the number of theoretical plates in the whole tower is more than 80, the two components can be completely Isolated to give 2,6-dimethylaniline.