Study On The Synthesis Of Monomenthyl Succinate Catalyzed By Supported 4-dimethylaminopyridine(DMAP)

Menthol is a traditional flavor cooling agent and food additive,which is widely used in the field of medicine and food.However,because of menthol has a strong irritant odor,the odor is particularly pungent when it is used in a large amount,and the cooling effect is not obvious when it is used in a small amount,so the application of menthol is limited to some extent.In order to overcome those problems,researchers have developed menthol derivatives,such as monomenthol succinate,which has the advantages of long cooling effect,pure odor and small amount,and it can be used as a kind of an ideal new cooling agent to replace menthol.Monomenthyl succinate is usually synthesized by homogeneous catalysis of 4-dimethylaminopyridine(DMAP),but there are many problems in the homogeneous catalysis process,such as complex separation process of catalyst and product,high cost and a small amount of catalyst residue in the product.In order to improve the safety of the product,reduce the production cost and simplify the separation process,in this paper,based on the previous work in the laboratory,DMAP was loaded on the surface of inorganic carrier to prepare the loaded DMAP,and heterogeneous catalyst was used to synthesize monomenthol succinate.Nano silica supported catalyst NS-DMAP was prepared by coupling reaction and N-alkylation with active 4-methylaminopyridine(MAP)as precursor and inorganic nano silica(NS)as carrier.The results showed that the maximum loading of NS-DMAP was 0.66 mmol / g at 130 ℃ for 22 hours.The catalyst was characterized by TG and IR.The results showed that DMAP was successfully loaded on the support.The optimum reaction conditions are as follows: the molar ratio of reaction substrate(menthol: succinic anhydride)1:2.5,reaction temperature 50 ℃,reaction time 15 h,stirring rate 500 rpm,catalyst dosage 20 g / L,the solvent is cyclohexane: acetone(v/v 3:2),at this time,the maximum yield of the product is 91.3%;after the reaction,the catalyst is recycled for 20 times,and the catalyst still has good catalytic effect and stability.Then,the maximum loading capacity and the optimum reaction conditions of MCM-41 and SG were studied.The results show that the maximum load of ccccccc is 0.88 mmol / g,and that of MCM-41-DMAP is 1.33 mmol / g,which is significantly higher than that of NS-DMAP.The two supported catalysts were characterized by IR and the results showed that DMAP was successfully loaded on the support.The two catalysts were used to catalyze the synthesis of monomenthyl succinate.Results showed that:(1)when SG-DMAP was used as catalyst,the reaction temperature was 50 ℃,the molar ratio of substrate(menthol: succinic anhydride)was 1:2.5,the reaction time was 20 h,and the amount of catalyst was 30 g / L,cyclohexane: acetone(v / v)3:2,the yield of monomenthol succinate reached the maximum,which was 80.2%;(2)when MCM-41-DMAP was used as catalyst,when the reaction temperature was 50 ℃,the molar ratio of substrate(menthol: succinic anhydride)was 1:2.5,the reaction time was 24 hours,cyclohexane: acetone mixed solvent(v / v)3:2,the catalyst dosage was 30 g / L,the yield of monomenthyl succinate reached the maximum,which was 77.2%.Similarly,the catalytic effect and stability of the two catalysts were not significantly damaged after 20 times of repeated use.In conclusion,the yield of monomenthol succinate catalyzed by NS-DMAP is the highest.So NS-DMAP was selected as the ideal catalyst.And then studied the separation,purification and identification of the products.In addition,the continuous reaction was carried out in a fixed bed reactor.The yield of menthol succinate can still reach 92.1% after 60 times of continuous reaction.Therefore,the method adopted in this paper provides a feasible way for the industrial production of menthol succinate.At the same time,the cost of the whole reaction process was estimated,and the profit from the production of 1 t of monomenthol succinate was between 108000 and 118000 yuan,which indicated that the NS-DMAP catalytic synthesis method of monomenthol succinate was not only environmentally friendly,but also low cost and high profit,with great economic value and industrial production prospect.