碳二亚胺是有机合成中重要的交联剂,在异氰酸酯工业中用作改性剂添加剂。因此,对它们形成的理解非常重要。在这项工作中,我们提出了理论B3LYP/6-31G(d)和SMD溶剂模型,以及在邻二氯苯(ODCB)溶剂中使用磷基催化剂(MPPO)从苯基异氰酸酯形成二苯基碳二亚胺(CDI)的实验研究。动力学实验基于放出的CO2的体积定量,在40和80°C之间的不同温度下。基于DFT计算,与以前的研究相比,我们设法构建了更详细的反应机制,并得到了实验结果的支持。DFT计算表明,该机构由两个主要部分组成,和第一部分的速率确定步骤,控制二氧化碳的形成,是具有52.9kJmol-1焓势垒的第一过渡态。实验活化能是从阿伦尼乌斯图(lnkvs.1/T)使用观察到的二阶动力学,得到的55.8±2.1kJmol-1与计算值吻合得很好,验证完整的机制,更好地了解从异氰酸酯生产碳二亚胺。
Carbodiimides are important crosslinkers in organic synthesis and are used in the isocyanate industry as modifier additives. Therefore, the understanding of their formation is of high importance. In this work, we present a theoretical B3LYP/6-31G(d) and SMD solvent model and experimental investigation of the formation of diphenylcarbodiimide (CDI) from phenyl isocyanate using a phosphorus-based catalyst (MPPO) in ortho-dichlorobenzene (ODCB) solvent. Kinetic experiments were based on the volumetric quantitation of CO2 evolved, at different temperatures between 40 and 80 °C. Based on DFT calculations, we managed to construct a more detailed reaction mechanism compared to previous studies which is supported by experimental results. DFT calculations revealed that the mechanism is composed of two main parts, and the rate determining step of the first part, controlling the CO2 formation, is the first transition state with a 52.9 kJ mol-1 enthalpy barrier. The experimental activation energy was obtained from the Arrhenius plot (ln k vs. 1/T) using the observed second-order kinetics, and the obtained 55.8 ± 2.1 kJ mol-1 was in excellent agreement with the computational one, validating the complete mechanism, giving a better understanding of carbodiimide production from isocyanates.