Synthesis Of2-Benzimidazolone Using Carbon Dioxide As Carbonylation Reagent

2-Benzimidazolone is a heterocyclic compound and can form strong intermolecular hydrogen bonds. It is an important intermediate in the synthesis of benzimidazole pigments, which are widely used in dying of plastics such as PVC, PE, PS, as well as in paint and printing ink industry.Thermodynamics of the reaction was analyzed, and the oxidative carbonylation reaction of o-phenylenediamine using carbon monoxide as a carbonylation agent is compared. Group contribution methods and empirical equations were applied to compute the thermodynamic properties of the reaction substances in different states. Gibbs free energy change and equilibrium constant of the reactions was calculated. The calculation results show that using o-phenylenediamine as the raw material and carbon dioxide as carbonylation reagent, the synthesis of2-Benzimidazolone is thermodynamically feasible. The reaction is an endothermic process, so elevated temperature is advantageous for the generation of2-Benzimidazolone.The solubility of2-Benzimidazolone in water, ethanol and DMF were investigated. Only0.3g2-Benzimidazolone can dissolve in130ml water above80℃. On the contrast.2-Benzimidazolone dissolved much better in DMF. Apelblat model can best fit the solubility data in ethanol and DMF, and the fitting curve equations were lnx=-3.605-709.158/T+0.544ln(T) and lnx=-96.981+2610.292/T+14.5071n (T) in the two solutions separately.Single-factor experiments were designed to study the impact of process conditions on the conversion rate. Solvent, base (organic and inorganic), pressure, temperature, reaction time were studied to determine the influence of the reaction condition on the conversion rate of starting material. Based on the experiment results, the optimal conditions for the industry production were as follow:o-phenylenediamine0.02mol, inorganic base0.02mol, H2O5mL, total pressure8.5MPa, temperature230℃, reaction time6hours. Conversion rate of o-phenylenediamine could reach92%under the optimal condition. In the experiment, inorganic base could be recycled for3-4times.The reaction kinetics under fixed pressure of3.5MPa was studied, the results show that the reaction of o-phenylenediamine and carbon dioxide comply with first-order reaction kinetics model. The kinetic equation was r=-dCo-PDA/dt=9.201×108exp(-88098/RT), and the activation energy was88.098KJ/mol.