Study On Preparing Glycine By Catalytic Hydrolysis Of Cyano Groups Using Metal Oxides

Glycine was prepared from hydroxyacetonitrile by a an improved hydantion process.The process has the advantages of simple steps and cheap raw materials,thereby reducing equipment investment and production costs.However,this process uses lye or acid in the production process,causing environmental pollution.Transition metal catalysts the hydrolysis of nitriles to carboxylic acids,this newly developed method avoids the use of excess strong acids and bases and meets the demands of the environmental friendly trend in organic synthesis.And this process has the advantages of high conversion rate,simple operation and simple equipment requirements.Among them,transition metal ions in the homogeneous catalyst have good selectivity to catalyze the hydrolysis of organic nitriles,but the metal ions cannot be recycled in the liquid phase reaction system,which also increases the difficulty of product separation.One important advantage when using immobilized catalysts and supported organocatalytic systems is that the catalyst can be recovered and reused.Moreover,it shows high selectivity and atomic economy,which is in line with the strategic trend of green sustainable development.Based on this parameter,strategies have been proposed for using solid catalysts to catalyze the hydrolysis of aminoacetonitrile to produce glycine from the concept of the green chemistry.In addition,the product was obtained with a good yield and high purity,thereby the composite catalyst has prospects.The main conclusions are as follows:(1)According to the thermodynamic calculation of the hydrolysis reaction of aminoacetonitrile,the main reaction is an endothermic reaction with a change in enthalpy of 117 kJ/mol within the experimental temperature range.The enthalpy change of the side reaction is about-15 KJ/mol,which is an exothermic reaction.The hydrolysis reaction is an endothermic reaction.Increasing the reaction temperature can increase the overall reaction rate,but it is conducive to the progress of side reactions.Obviously,the higher the reaction temperatures,the lower the yield of glycine is observed.Therefore,the suitable reaction temperature should be controlled between 55-65℃.Through chemical equilibrium analysis,the side reaction is an irreversible reaction.And the by-product iminodiacetonitrile can further form a polymer,which affects the hydrolysis of the reaction system and reduces the yield of glycine.(2)Macro-kinetic investigation results demonstrate that the hydrolysis reaction of aminoacetonitrile is a first-order kinetics equation,with an Ea of 4.624 kJmol-1 and the A of 0.111 min-1.In the reaction,the reaction activation energy is smaller and the reaction rate is faster,which is a diffusion control process.It can be seen from the half-life of the reaction that when the reaction temperature is 45℃,the half-life is 35.795 min.And when the reaction temperature is 85℃,the half-life is 29.858 min.The results indicate that the temperature has a certain effect on the reaction speed.(3)The enthalpy of activation and the entropy of activation is calculated by using the Eyring Equation with,ΔH≠=1.798±2.144 KJmol-1,ΔS≠=-272.596±6.631 Jmol-1K-1 and P=5.761 × 10-15.A very small steric factor was found in the ion-generating reaction(P as low as 5.761 ×10-15,ΔS≠ as low as-272.596).In this type of reaction,negative entropy can be activated because an increased relative order(relative to the ground state)is established in the transition state of the reaction.Similarly,the smaller representation helps to promote the activation of exchangeable sites and metal ions.(4)From the preparation of hydroxyacetonitrile,and then the amination of hydroxyacetonitrile to aminoacetonitrile,the use of a composite catalyst to synergistically catalyze the hydrolysis of aminoacetonitrile and hydroxyacetonitrile in the reaction solution of aminoacetonitrile,thereby obtaining crude glycine.Finally,the catalyst can be recycled and reused,and the mother liquor can be decolorized,forming a complete process flow.The yield of glycine and IDA is maintained above 90%and 5%(calculated based on aminoacetonitrile),respectively,and the content of crude glycine is about 85%.(5)The prepared composite catalyst can effectively catalyze the hydrolysis of aminoacetonitrile and iminodiacetonitrile,and overcomes the problems existing in the original process,such as the use of strong acid and strong base,low yield,high economic cost,and high environmental protection pressure.At the same time,the yield of glycine prepared by the original process is increased by about 13%.The original process uses NaOH to catalyze the hydrolysis of aminoacetonitrile,and the yield of glycine is only about 77%.The composite catalyst has stable hydrolysis performance after being soaked,washed,and regenerated at a high temperature of 600-700℃,and can be reused 8 times.