Study On The Conversion Of Carbohydrates Into Halogenated Methyl-furfural In Deep Eutectic Solvents

Biomass is the most abundant and renewable resource on the earth,which can be applied to energy,medicine and chemical industry,and attracted more and more researchers’ attention.The conversion of carbohydrates into platform chemicals and value-added biomass-based chemicals is the main research direction in the world for efficient utilization of the biomass resource.In this thesis taking biomass carbohydrates as the raw material,a series of studies were conducted on the catalytic conversion of carbohydrates to halogenated methyl furfural in the new Deep Eutectic Solvent system(DESs).Meanwhile,the catalysts,reaction conditions,reaction mechanism,separation and purification were studied.Research results obtained from those studies are as follows.Firstly,DES consisting of fructose and Choline chloride(ChCl)has been proved an excellent reaction system,a novel method was put forward in this thesis for the preparation of new platform molecule 5-chloromethyl furfural(5-CMF)in the DES/MIBK biphasic reaction system.During the catalytic conversion of carbohydrates into 5-CMF under the DES/MIBK system,the acidity has a great influence on the reaction efficiency.The results show that the Lewis acid salt AICl3 6H2O has good effect on the catalytic dehydration of fructose to produce 5-CMF,accompanying by a small amount of 5-hydroxymethylfurfural(5-HMF)and the residue.Comparing to traditional methods,this method was more mild.In the study of different DES systems,only the DES formed by fructose and choline chloride could produce higher yield of 5-CMF under the catalysis of AICl3 6H2O due to the different composition of DES.It may be that fructose and AICl3 6H2O can become a part of DES as hydrogen bond donor,thus greatly improving the feed amount of raw materials,making the catalyst is in close contact with the raw materials and the reaction effect is better.Moreover,the possible mechanism of the carbohydrate dehydration into 5-CMF was schemed on the experimental data obtained.It was demonstrated that both ChCl and AlCl3 6H2O could provide chlorine source in the reaction,but both were indispensable.Then,based on the research on the mechanism of 5-CMF,a novel method of preparing 5-bromomethylfurfural(5-BMF)in DES/MIBK biphasic system was first proposed in this paper.It was found that the catalyst with high Lewis acidity could effectively promote the conversion of carbohydrates.When Al2(SO4)3 used as the catalyst,the fructose could be effectively converted into 5-BMF.In the reaction condition of substrates of 0.9 g fructose,3.6 g ChCl dosage,5 mmol catalyst loading,24 g MIBK co-solvent,120 ℃ reaction temperature and 5 h reaction time,a highest yield 5-BMF of 49.53%was obtained.The DES mixture could be effectively recycled after the reaction,only a little decrease of 5-CMF yield was detected after the DES system being recycled for four times.Other carbohydrate such as glucose,starch,inulin and sucrose were also exerted in this biphasic reaction,and suitable 5-HMF and 5-BMF yields were achieved.The reaction product was isolated and purified by column chromatography with the mass ratio of Dichloromethane(DCM):n-hexane mass was 3:2 as eluent,which can be obtained high-purity 5-BMF effectively.Last but not least,the thesis also studied the possibility of different carbohydrates and choline chloride formation of DES,the result have shown that sucrose and maltose can be more easily formed the DES with choline chloride.However,starch and other polysaccharides will not be able to form DES with choline chloride effectively,because of its long carbon chain.Therefore,the study of different carbohydrates to prepare 5-CMF using the DES form with choline chloride and aluminum chloride.In the reaction condition of mass ratio of starch and ChCl was 1:4,24 g MIBK co-solvent,120 ℃reaction temperature and 5 h reaction time,a highest yield 5-CMF of 24.70%was obtained.Adding HC1 to the system can effectively promote the reaction and provide a chlorine source for the generation of 5-CMF.However,the introduced water destroys the DES system,therefore,without destroying the case of DES,the most appropriate amount of HCl feed was 500 μL.Other carbohydrates in the DES/MIBK biphasic system with HCl catalyst could also be effectively converted into 5-CMF,higher yield was obtained while the biomass feedstock treated after ball-milling.