Study On The Synthesis And Coordination Properties Of Glucosaminic Acid

Glucosaminic acid (2-amino-2-deoxy-D-gluconic acid, GAA) is one of the carbohydrate units to manufacture various biotic substances. It has various physiological functions. It has extensive application prospects in the food, cosmetic and pharmaceutical industries.There are few literatures on the synthesis of glucosaminic acid. The coordination properties of glucosaminic acid were explored little.Therefore, one of the objects of the present investigation was to explore some novel highly efficient synthesis methods of glucosaminic acid and discover the corresponding mechanisms. The other was to study the coordination equilibria of glucosaminic acid with metal ions in order to obtain the corresponding stability constants and thermodynamic functions which had not been found in the present literatures. This investigation has the important theory significance and the practical application value to the exploitation of GAAThe bimetallic catalytical oxidation method and the electrocatalytical oxidation method were first used to explore the highly efficient synthesis of glucosaminic acid. An improved method on traditional catalyst preparation methods was applied. The supported Pd-Bi/C catalyst was prepared by successively incorporating the active components Pd and Bi into the supports by impregnation. Then a novel surface redox reaction in the liquid phase was explored to activate the catalyst. The synthesis of glucosaminic acid was done with glucosamine chloride as the material and molecular oxygen as the oxidant. Optimization of the oxidation reaction conditions was done with orthogonal method. The mechanism of the bimetallic catalytical method was discussed on the results of the microstructure of the catalyst and the thermodynamic study on the catalytical process. The result shows: 1) The bimetallic catalytical oxidation method with Pd-Bi/C has high selectivity (>90%), mild conditions(30℃), shorter reaction time(6h) and easy manipulation, the possibility of conducting the oxidation in one step in a single reaction vessel. Moreover, the catalytical process is environmentally clean and the catalyst can be recycled for 7 times with almost unreducing activity. The Pd-Bi/C catalyst prepared by a new surface redox reaction in the liquid phase is very stable. There is neither bismuth nor palladium was detected in the product. The product can reach food and pharmaceutical grade. The yield of the bimetallic catalytical oxidation method is 70.0% and the method is a novel synthesis for glucosaminic acid with promising application prospect. 3) A novel mechanism model as "the catalytical mechanism of coordination and transmission with synergistic effect" was proposed. The steps of the mechanism are as follows: first, the complex of Bi(â…¢) with the reactant was formed in the reaction solution, the complex was accurately located on Pd atom which was deposited on the surface of the catalyst with the synergistic effect of Bi and Pd. Then the complex was combined with water to form the corresponding hydrate. Successively, the adsorptive hydrate was dehydrogenated. The molecular oxygen was combined with Bi located on the surface of Pd to form "Bi₂O₃, the state of the oxygen now was proposed in the form of lattice oxygen. Water was formed by the lattice oxygen in "Bi₂O₃" with the active hydrogen from the hydrate. Thus, bismuth was regenerated to Bi⁰, The hydrate was oxidized to the corresponding acid in complex state, Bi(III) was released into the solution from the complex of the acid with the synergistic effect of Pd. Then the released Bi(â…¢) was recomplexed with the reactant to enter the next cycle of the oxidation process. The mechanism could give perfect interpretations on various experimental results, which provided the evidence for the rationality of it. This is an innovation and breakthrough in catalytical theory.The paired electrocatalytical method was first used to explore the highly efficient synthesis of glucosaminic acid from glucosamine chloride. The microscopic reaction process on the surface of the electrode and the reaction kinetics of the electrocatalytical oxidation were studied by cyclic voltammetry method and the factor which effects the activity of the electrodes was studied. Then the mechanism of the electrocatalytical oxidation was disclosed. The UPD modification electrode method was used to improve the catalytical performance of the electrodes. On the basis of the modification of the electrode, the paired electrocatalytical method was applied to further improve the spatiotemporal efficiency of the reaction. The result shows: 1) Gold is the active electrode material for the electrocatalytical synthesis of glucosaminic acid. 2) The adsorption of anions is the critical factor which affects the activity of the electrodes. The electrocatalytical oxidation mechanism was proposed. Under the guidance of it, the paired electrocatalytical synthesis for glucosaminic acid was successful. The spatiotemporal efficiency of the reaction was improved greatly. 3) The steps of the mechanism are as follows: firstly, the adsorptive species Au(OH)^(1-λ)- was formed, which can catalyze the oxidation reaction, then the combining hydrogen on the C1 of the glucosamine is dissociated to form the adsorptive free radical. The step is the rate-determining step of the oxidation reaction. The step shows the kinetic characteristic of a first order reaction under the experiment condition. Subsequently, the adsorptive free radical was oxidized to intermediate lactone of glucosaminic acid. Then the lactone was transformed to glucosaminic acid by hydrolysis. 4) In the electrocatalytical synthesis of glucosaminic acid in alkaline medium, the current efficiency can reach 99.5%. The value is 70.7% in neutral medium. The yield is higher and the reproducibility better compared with the enzymatic, fermentative and bimetallic catalytical synthesis. Moreover, the paired electrosynthesis of glyoxylic acid and glucosaminic acid was feasible and the better experiment results were obtained on both of the electrodes. The mean yield of glucosaminic acid is 67.5%. The reaction time is 4 h. Compared with the bimetallic catalytical oxidation method, the electrosynthesis method has brighter application prospect.Two simple and convenient methods as spectrophotometry and pH-potential titration were adopted to study the coordination properties of glucosaminic acid with metal ions and the corresponding thermodynamic functions. The results are as follows: the complexation molar ratio with Cu(â…¡) is 1:2, the molar adsorptivity of the complex is 39.906 L·mol^-1·cm^-1 at 630 ran, the stability constantβ_n is 6.24×10⁵. The calculated concentration of the complexing agent is in accord with the given one, which provided the evidence for the rationality of the used dual-series linear regression method. The thermodynamic functions in the formation reactions of Ni(â…¡), Co(â…¡) and Zn(â…¡) with glucosaminic acid were determined by the method of pH-potential titration. The stability constants of the glucosaminic acid complexes are almost equal to the corresponding ones of the alanine and norleucine, but their enthalpy changes are larger and the entropy changes are smaller. Therefore, it was inferred that the alcoholic hydroxyl groups of glucosaminic acid might take part in the complex formation.