Hydrolysis Of Carbohydrates In To5-Hydroxymethylfurfural Catalyzed By Ionic Liquids

The efficient transformation of carbohydrates into5-hydroxymethylfurfural (5-HMF)—which is regarded as a versatileplatform molecule and used in the production of fine chemicals,pharmaceuticals and polymers—is a key step in the use of carbohydrates toproduce liquid fuels and value-added chemicals. Recently, the dehydrationof carbohydrates to5-HMF with room temperature ionic liquids (ILs),which were used as reaction media in the synthesis of organic materialsbecause they are nonvolatile, nonflammable, highly polar, and easy toseparate from reactants and products, has attracted great interest as a wayof producing liquid fuels from renewable resources, but all ILs reported areneutral or acidic, and promote dehydration due to enhanced dissolution ofcatalysts and substrates.In this paper, efficient processes in which ILs have been used as acatalyst—rather than as a solvent—in the conversion of carbohydrates(such as fructose, glucose, sucrose, cellobiose, starch and cellulose) into5-HMF bave been developed. Br nsted acidic was applied to thedehydration of fructose, followed by alkaline and hydroxyl ILs, which were frist used in conversion of carbohydrates. Moreover, several kineticparameters for fructose dehydration with [BMIM]₃PW₁₂O₄₀and[BMIM]OH and possible mechanisms of the dehydration of carbohydratescatalyzed by ILs (include acidic, alkaline and neutral ILs) were obtained.Fristly, Br nsted acidic IL,[BMIM]₃PW₁₂O₄₀and [BMIM]3PW₁2O₄0,heteropolyacid salts of an IL-forming cation functionalized with apropanesulfonate group, were used as a catalyst in the conversion offructose to5-HMF. The maximum yield of5-HMF was99.14%at120oCafter2h using sec-butanol as solvent, and the catalyst can be separated in asimple process at the end of the reaction and reused without loss of activity.Specially, during the process,[BMIM]₃PW₁₂O₄₀acted as a "reactiontemperature controlled liquid-solid" catalyst.5-HMF yields achieved fromglucose, sucrose, starch and cellulose were7.65%,31.09%,16.17%and6.94%respectively. It can be concluded that the ismerization of glucose ischief in hydrolysis of carbohydrates.Secondly, br nsted alkaline ILs,[EMIM]OH,[BMIM]OH,[HMIM]OH,[OMIM]OH,[BMIM]₂CO₃,[BMIM]PhCOO,[BMIM]OAc and [AEMIM]BF₄were applied into the preparation of5-HMF. It was found that[AEMIM]BF₄exhibited excellent activity in the transformation ofcarbohydrates into5-HMF. The highest yield of97.60%was also beenachieved catalyzed by [AEMIM] BF₄in DMSO at160oC with a mass ratioIL:fructose of0.5. Furthermore,5-HMF yields achieved from glucose, sucrose, cellobiose, starch and cellulose were45.25%,68.21%,34.25%,46.77%and26.07%, respectively. Conversion of5-HMF into productssuch as levulinic acid and formic acid is the main side reaction underalkaline condition.Thirdly, hydroxyl ILs,[C₂OHMIM]BF₄was used as the catalyst for theconversion of carbohydrates into5-HMF for inhibiting conversion of5-HMF into levulinic acid and so on.5-HMF yields achieved from glucose,sucrose, cellobiose, starch and cellulose were67.30%,76.19%,33.49%,42.93%and41.66%, respectively. A yield of nearly100%was achieved inthe dehydration of fructose.Finally, several kinetic parameters for fructose dehydration with[MIMPS]3PW₁2O₄0and [BMIM]OH were obtained. Moreover, theactivation energy of fructose conversion and pre-exponential factor werealso determined. The kinetic equations have been received. Furthermore,formation mechanism of conversion carbohydrates into5-HMF catatlyzedby alkaline ILs was proposed:(1) hydrolyze carbohydrates into glucose;(2)isomerization of glucose into enolate isomers according to LBAE reactionin weak alkali conditions;(3) elimination of H2O, isomerization andhemiacetal to form five-ring;(4)-elimination to get final product.