Through the optimization analysis of main equipment operating parameters, the optimum operating conditions of reactive distillation column are as follows: the molar ratio of methanol to propylene carbonate is 4: 1, the reflux ratio is 3 ~ 5, the pressure is 1.6 ~ 1.8 kPa, and the temperature is 65 ~ 67℃. Under these conditions, the yield of DMC and propylene glycol is the highest, and methanol and DMC form a * * * boiling substance in the distillation section. The boiling of methanol and dimethyl carbonate in the pressurized distillation column was changed from atmospheric boiling to high pressure boiling, which improved the separation degree of the two and increased the yield of dimethyl carbonate. Using "green chemical" dimethyl carbonate instead of phosgene to synthesize methyl 2,4-toluene dicarbamate and then decompose it to produce toluene diisocyanate, which has the advantages of mild reaction conditions, cheap catalyst and only methanol as a by-product. If it is combined with methanol oxidative carbonylation of dimethyl carbonate, it can form a "zero emission" green synthesis process, which is an important development direction of clean chemical industry.
Firstly, the purity of the main product methyl 2,4-toluene dicarbamate was prepared by recrystallization, and its purity was detected by CHN element analyzer, and it was qualitatively analyzed by advanced detection methods such as mass spectrometry, infrared spectroscopy and nuclear magnetic resonance spectroscopy. Methyl 2- methyl -5- aminobenzoate was prepared by preparative liquid chromatography, and it was qualitatively analyzed by mass spectrometry and infrared spectroscopy. The by-product polyurea was qualitatively analyzed by liquid chromatography-mass spectrometry (LC-MS). Thus, all the main and by-products of the reaction of synthesizing methyl 2,4-toluene dicarbamate from dimethyl carbonate and 2,4-diaminotoluene were determined.
Secondly, a set of applicable and efficient HPLC analysis system for simultaneous detection of reactants, main products and by-products was established. Chromatographic conditions were: column RP C- 18, mobile phase V (methanol): V (water) =5:5, flow rate 0.6ml/min, ultraviolet detection, wavelength 254nm. The main product, methyl 2,4-toluene dicarbamate, was quantitatively analyzed by external standard method, and the accuracy and recovery rate of the experimental results were tested, with good results.
Thirdly, the catalyst was screened and its activity order was determined: zinc acetate >; Lead oxide >: sodium methoxide >: basic zinc carbonate >: zinc oxide = basic copper carbonate. Among them, zinc acetate, lead oxide and sodium methoxide have good catalytic performance for the synthesis of methyl 2,4-toluene dicarbamate from dimethyl carbonate and 2,4-diaminotoluene.
Fourthly, methyl 2,4-toluene dicarbamate was synthesized from dimethyl carbonate and 2,4-diaminotoluene with sodium methoxide as catalyst. It was found that adding methyl formate could significantly improve the yield of methyl 2,4-toluene dicarbamate. The intermediate products 2,4-toluenediamide and N-(2- methyl -5- amino) phenylformamide were characterized by gas chromatography-mass spectrometry and infrared spectroscopy, and the reaction mechanism was preliminarily speculated. The factors affecting the reaction were studied and the suitable reaction conditions were obtained. The yield of methyl 2,4-toluene dicarbamate can reach 59.75%.
Fifthly, the synthesis of 2 from dimethyl carbonate and 2,4-diaminotoluene catalyzed by zinc acetate was studied. 4. The reaction of methyl toluene dicarbamate. The catalyst was characterized by Xap, and the reaction solution was qualitatively analyzed by gas chromatography-mass spectrometry. It has been determined that the deactivation of the zinc acetate catalyst is due to its further reaction with methanol, a by-product of the reaction, which produces methyl acetate, water and zinc oxide with no catalytic activity for the synthesis of methyl 2,4-toluene dicarbamate. Through gas chromatography analysis, it is determined that the residual pressure in the autoclave is caused by carbon dioxide, and dimethyl carbonate is hydrolyzed to produce methanol and carbon dioxide. The factors affecting the reaction were studied and the suitable reaction conditions were obtained. The yield of methyl toluene dicarbamate can reach 89.32%.
Sixthly, the synthesis of methyl l _ 4 toluene dicarbamate from dimethyl carbonate and 2,2-dihydrotoluene catalyzed by lead oxide was studied. The reaction has an induction period, which is closely related to the surface state of lead oxide catalyst. The lead oxide catalyst pretreated by dimethyl carbonate was transformed into a new phase, PbOO, which entered the flash M, and the induction period disappeared. The chemical reaction is at a new stage. From the surface of 0mz, oH functional groups played an important role in the reaction. On this basis, the reaction mechanism was speculated. The effects of reaction temperature and time on the reaction were studied, and the suitable reaction conditions were obtained. The yield of methyl 2,4-toluene dicarbamate can reach 865438 0.8%. Ionic liquids have become the focus of researchers' attention because of their unique physical and chemical properties, and have been successfully applied to a variety of catalytic reactions. In this paper, the advantages of dimethyl carbonate and ionic liquid are effectively combined, and some organic reactions involving dimethyl carbonate catalyzed by ionic liquid are studied. It mainly includes two parts: the first part is the methoxycarbonylation of dimethyl carbonate catalyzed by ionic liquid; The second part is the methylation of dimethyl carbonate catalyzed by ionic liquids. In the synthesis of nitrogen heterocyclic ester by the methoxycarbonylation of dimethyl carbonate and nitrogen heterocyclic compound catalyzed by ionic liquid, ionic liquid was used instead of strong base as catalyst to catalyze the methoxycarbonylation of dimethyl carbonate and nitrogen heterocyclic compound to synthesize nitrogen heterocyclic ester efficiently and green. Under the optimized reaction conditions, the selectivity and yield of indole-1- methyl formate can reach 100% and 96% respectively.
By studying the reaction of different nitrogen heterocyclic compounds with dimethyl carbonate, it was found that the steric effects at the 2-position of indole was an important factor affecting the reaction activity of indole compounds. The effects of different ionic liquids on the reaction activity were investigated. The results show that the catalytic activity of ionic liquids with imidazole cation as 2-position hydrogen atom is obviously better than that with imidazole cation as 2-position methyl atom. The hydrogen atom at the 2-position of imidazole cation forms a hydrogen bond with the carbonyl oxygen atom of dimethyl carbonate, which activates the dimethyl carbonate molecule, reduces the reaction energy barrier and promotes the reaction. The ionic liquid can be recycled for 4 times, and the reaction activity has not decreased. In the process of synthesizing 2- phenylpropanenitrile compounds by methylation of dimethyl carbonate and substituted phenylacetonitrile compounds catalyzed by ionic liquids, ionic liquids were used as catalysts instead of inorganic salts or molecular sieves with low catalytic activity. The effects of reaction temperature, reaction time, water content and catalyst dosage on the reaction were investigated with phenylacetonitrile as the substrate.