Study On The Hydrolysis Kinetics Of Dimethyl Oxalate

Oxalic acid is a widely used organic chemical material. In recent years, thedemand of oxalic acid is increasing continually with the constant expansion ofapplication in the pharmaceutical industry and rare earth processing industry. Thetraditional processes for oxalic acid production have the problems of high costs andgeneration of toxic pollutants. Therefore, it is important to develop green process ofoxalic acid. With the development of green chemistry research progress,producing the corresponding oxalate by carbon monoxide coupling system, and thenobtaining oxalic acid via the hydrolysis of oxalate is getting more and more attention.In order to develop the industrial production process of oxalic acid via the hydrolysisof dimethyl oxalate, the paper focused on the hydrolysis kinetic model of dimethyloxalate.The method of High Performance Liquid Chromatography was established todetermine the components of the hydrolysis system. After investigating the influencesof the flow rates, mobile types, compositions and pH on the separation effects, theappropriate analysis conditions were confirmed. The method displayed high averagerecoveries for the samples ranged from98.24%to103.75%and good precision (RSD)ranged from0.19%to0.75%. It was simple, fast and accurate enough to apply to thehydrolysis system of dimethyl oxalate.Through the analysis of the mole fraction of different materials and the variationof overall selectivity of products, the hydrolysis of dimethyl oxalate was consideredas series reaction. A mechanism for the auto-catalyzed hydrolysis reactions wasproposed, in which involves the attack of the water upon the protonated ester, protontransfer, and elimination of alcohol and protons. Adopting the widely recognizedacid-catalyzed hydrolysis mechanism, we assumed that the nucleophilic substitution israte determining step. Kinetic expressions, including the DMO hydrolysis and OAformation have been developed to describe auto-catalyzed hydrolysis behavior, andthe models proposed provide a good agreement with the experimental data. Theexpressions of kinetic parameters and equilibrium constants have been determined.The kinetic expressions of DMO hydrolysis and OA formation are expressed as: The standard reaction enthalpies and considered in this workresulted to be8.97kJ/mol and14.35kJ/mol respectively, which are close to thevalues calculated from the standard enthalpy, and both reactions were also found to beendothermic.In addition, the effects of temperature, initial reactants molar ratio, agitation andthe addition of oxalic acid on reaction were investigated. The experimental resultsshowed that large initial reactant molar ratio and high operating temperature arebeneficial to the formation of OA.