Preparation Of Glucuronic Acid By Selective Oxidation Of Primary Hydroxy Of Methyl Glucoside

Based on its important role in human health,glucuronolactone is aneffective medicine of protecting the liver and a new type of functional food andbeverage additive.The current route of preparingglucuronolactone by nitric acid oxidation from starch has been criticized of difficult separation,poor utilization rate of raw material,high energy consumption and heavy pollution,which obviously cannot meet the market needs and requirements of the development of green chemistry.Considering the advantages and disadvantages of various methods,microwave irradiation and activemanganese dioxide are combined together and applied into the synthesis ofglucuronic acid innovatively.The C-6 primaryhydroxy of methyl glucoside can be selectively oxidated to aldehyde by activemanganese dioxide under microwave irradiation condition.And then the aldehyde is oxidated to corresponding carboxyl by second stage oxidation treatment,which is hydrolyzed subsequently to achieve glucuronic acid product.According to the references,activemanganese dioxide has been prepared at different temperature and been characterized by a series ofmethods such as XPS ?XRD?SEM?BET?TGA.Activemanganese dioxide prepared at different temperature are applied into the synthesis ofglucuronic acid.We have studied the effect of reaction time,reaction temperature and the mass ratio of methyl glucoside and active MnO₂ on the yield of glucuronic acid.The results show that whenactive manganese dioxide and methyl glucoside react in a ratio of 4:1 at80? for 2 h,glucuronic acid can reach the highest yield to be 79%.HPLC and HPLC-MS have been utilized to analyze the hydrolyzed product,and the results prove that the obtained product is glucuronic acid.What is more,we investigate the effect of preparation temperature of active MnO₂ on the yield of glucuronic acid and results show that the active MnO₂ preparared at 70?displays better oxidizability and selectivity.In order to figure out the relation between crystalline degree with oxidizability of active MnO₂,activemanganese dioxide prepared at different temperature are calcinated and then characterized by a series ofmethods such as XPS?XRD?SEM?BET ? TGA.Active MnO₂ after calcination is ?-MnO₂ with high degree ofcrystallization,whose porous structure changes a lot.Different calcinated tenperatureof active MnO₂ do not make a big difference on the yield of glucuronic acid,indicating that crystalline degree is not the determinant of the yield of glucuronic acid.Based onprimary hydroxyl oxidation reaction,the influence factors of second oxidation reaction are discussed,including reaction time and reaction temperature as well as molar ratio.The results indicate that glucuronic acid can reach the highest yield when H₂O₂ and primary oxidation reaction product react in a ratio of 2:1 at 80?for 2 h.Comparing withcurrentmethod of preparing glucuronic acid,the approach armed with active MnO₂ and microwave irradiation has many advantages such as low energy consumption,easy after-treatment and simple device.Along with more and more attention has been brought into microwave chemistry,the combinedapplication of microwave and active MnO₂ will have good prospects.