Synthesis Of Glucuronic Acid And Glucurolactone From Methyl Glucoside By Catalytic Oxidation Over Mn²⁺/h₂o₂ System

D-(+)-Glucofuranurono-6, 3-lactone is abbreviated as Glucurolactone. Glucurolactone is used as liver antidote usually and conditioning agent with immune function in medical field. On the other hand, glucurolactone is also used widely as the main additive in drinks,foods, diet pills, cosmetic, and so on.The main synthetic methods of glucuronolactone have bio-fermentation, hydrolysis and chemical oxidation. Among those ways, bio-fermentation and hydrolysis processes are more complex, low yield and high cost. Chemical oxidation is widely used in the preparation of glucuronic acid and its lactone. The present industrial route of producing glucurolactone is nitric acid oxidative method using starch as the precursor. This technology has a series of disadvantages such as its longer production time, the serious environmental pollution, the low yield, the difficulty of separating the product and the high energy consumption. The catalytic oxidation which use glycoside as raw materials and H₂O₂ as oxidant have a series of advantages such as resource-efficient, environment-friendly, low energy consumption. So it accords with the development requirements of green chemistry.The catalyst system was composed of the transition metal ions (Fe²⁺, Cu⁺, Mn²⁺, Co²⁺) and H₂O₂, which could produce hydroxyl radical in this system. The hydroxyl radical is the active components which could oxidate primary hydroxide of glycoside selectively. The glucuronic acid and its lactone were obtained through hydrolysis and esterification of the oxidative intermediate. Compared the catalytic ability of different metal ions, the Mn²⁺ system was found having the best catalytic effect. The oxidative mechanism of glycoside by Mn²⁺/H₂O₂ system was studied briefly. Glucuronic acid could be monitored by visible spectrophotography and high performance liquid chromatography (HPLC). Glucurolactone was obtained and purified by esterification and crystallization subsequently, and its purity was confirmed by melting point tester, infrared spectroscopy, and high performance liquid chromatography respectively.The conditions of catalytic oxidation, including the component of catalyst, reactant ratio, H₂O₂ concentration, pH and reaction time were discussed and the influences of temperature, reaction time and the kind of the acids on the hydrolysis reaction process were also discussed in the paper. Orthogonal experimental results show that the value of pH was the most important factor on yield, compared with the molar ratio of H₂O₂ and glycoside, the molar ratio of Mn²⁺ and glucoside, reaction time. The optimized conditions was as follows: the value of pH was 10, reaction time was 4h, the molar ratio of H₂O₂ and glycoside was 3:1, the molar ratio of Mn²⁺ and glucoside was 0.02:1. The optimal condition of hydrolysis reaction was as following: H2SO4 used as catalyst, pH value was 1, temprerature was 90℃and reaction time was 100min. Under these conditions the yield of glucuronic acid could reach 35.25%, the yield of glucurolactone could reach 23.5%, and the total yield could reach about 58.75%. In the meantime, no peak of impurity appeared from HPLC, this result showed that the Mn²⁺/H₂O₂ system had good catalytic activity and selectivity for the oxidation of primary hydroxyl.The catalytic oxidation of glycoside by Mn²⁺/H₂O₂ system had better activity and selectivity. This process adapted the demand of green chemistry by its mild reaction conditions, low energy consumption and environment-friendly, and it had a good prospect for industrial applications.