Synthesis Mechanism Of Pyrrole Compounds Based On In-situ Mid-infrared Monitoring Technology

In this paper,the synthesis reaction paths and kinetics of pyrrole derivatives are studied by in-situ mid-infrared spectroscopy and density functional theory calculation.The intermediates were identified and quantified by real-time mid-infrared spectroscopy and two-dimensional correlation spectroscopy(2DCOS)analysis.On this basis,the effects of operating conditions and technological conditions of the reaction process were studied.In addition,the kinetic parameters of the reaction steps were calculated according to the component concentration of the time series determined by the infrared quantitative model.The reaction conditons,ways and kinetics were analyzed by online infrared characterization and theoretical calculation.When the experiment used2,5-hexadione and ethanolamine as raw materials and methanol as solvent to synthesize 1-(2-hydroxyethyl)-2,5-dimethylpyrrole,the reaction microscopic ways were obtained as follows: 2,5-hexadione and ethanolamine underwent nucleophilic addition to form the hemiketone structure,which underwent further nucleophilic addition to form a ring,followed by β-elimination of the water product1-(2-hydroxyethyl)-2,5-dimethylpyrrole.The optimal reaction conditions selected in this study were reaction temperature 50℃,automatic dropping at 3g/min,reaction feed ratio 1:1,reaction time 3h,the rate constants and activation energies of each step were calculated.When 2,5-hexadione and butyl carbamate were used as raw materials in the experiment,n-alkoxycarbonyl-2,5-dimethylpyrrole was synthesized under acidic catalyst,and the reaction microscopic ways were obtained as follows: 2,5-hexadione and butyl carbamate underwent nucleophilic addition over a catalyst to form the hemiketone structure.The hemiketone structure was dehydrated and a molecule of water was removed to form the enamine structure.The enamine structure was further added to form a ring,followed by the elimination and loss of a molecule of water to form the n-alkoxycarbonyl-2,5-dimethylpyrrole.The optimum reaction conditions were obtained as follows: reaction temperature 77℃,automatic dropping at 3g/min,catalyst amount 0.004 mol and ethanol as solvent reaction 6.5h.The reaction to generate the structure of enamine is the decisive step,and the reaction is divided into two steps,the rate constants and activation energies of each step were calculated.respectively.By infrared online real-time monitoring method of organic synthesis reaction,not only can effectively in the reaction process of real-time monitoring the change of components for the study of the microscopic process and kinetics of chemical reaction to provide strong evidence,can also be applied to optimize the reaction conditions and reaction process control,the final purpose of improving the reaction conversion rate and yield and other purposes.