Separation And Purification Of N-acetylglucosamine

N-acetylglucosamine(GlcNAc)is one of the basic constituent units of chitin,which has many important physiological functions.At present,the chemical synthesis of GlcNAc is mainly prepared by acetylizing glucosamine hydrochloride(GAH)obtained by the acid hydrolysis of chitin with acetic anhydride.Since the chemical synthesis of GlcNAc contains a certain amount of GAH,this paper studies the separation and purification process of GlcNAc,establishes the rapid analysis method of GAH in GlcNAc,measures the solubility of GlcNAc and GAH,and investigates the effect of separation method on the yield and purity of GlcNAc.The main research contents and conclusions are as follows:(1)The determination of GAH content in GlcNAc was studied and the effect of GlcNAc content on the determination of GAH was investigated.The experimental results show that the addition of GlcNAc has a great influence on the determination results when measured by ultraviolet spectrophotometry.When the ratio of GlcNAc to GAH is 0:1,1:1,2:1,3:1,the values of ARD are 5.38%,15.32%,15.95%and 15.21%,respectively.An analytical method for the determination of GAH content by automatic potentiometric titration was established.The results show that the stability and accuracy of the automatic potentiometric titration method is satisfactory.The presence of GlcNAc has no effect on the determination of GAH content,and the ARD value is 0.15%.(2)The solubility of GlcNAc in water,methanol,ethanol,n-propanol,acetone,water+ethanol,water + acetone at different temperatures was measured by static method.The experimental results show that the solubility of GlcNAc in the same solvent increases with the increase of temperature.The solubility in the mixed solvent decreases as the molar fraction of ethanol or acetone increases.The solubility of GlcNAc in pure solvent was correlated by Van't Hoff equation,modified Apelblat equation,?h equation and the modified Apelblat equation has the best correlation effect.The solubility in the mixed solvent was correlated by the Jouyban-Acree model,and the fitting results were in good agreement with the experimental results.The dissolution thermodynamic parameters of GlcNAc in different solvents were correlated based on the Van't Hoff equation.The solubility properties indicate that the dissolution process is endothermic and spontaneous.(3)The solubility of GAH in water,water+ethanol,water+acetone solvent was measured by static method and compared with the solubility data of GlcNAc in the same solvents.The results show that the separation of GAH and GlcNAc is more favorable with water as solvent,and the separation process is carried out by using water-cooling crystallization method and partial dissolution method.It was found that there was no crystal precipitation when the temperature was lowered from 50 ? to 5 ? by the cooling crystallization method,and the purpose of separation between the two could not be achieved.GlcNAc with a purity of 99%could be obtained when purified by partial dissolution method,and GAH was removed by adding a small amount of water.The yield of GlcNAc was related to the ratio of GlcNAc and GAH initially added.The ratio of GAH/GlcNAc in the mother liquor was between 0.76-0.79,which can be returned to the synthesis reaction process.