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首页> 美国卫生研究院文献>Polymers >An Ab Initio Investigation of the 44′-Methlylene Diphenyl Diamine (44′-MDA) Formation from the Reaction of Aniline with Formaldehyde
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An Ab Initio Investigation of the 44′-Methlylene Diphenyl Diamine (44′-MDA) Formation from the Reaction of Aniline with Formaldehyde

机译：从苯胺与甲醛反应形成44-亚甲基二苯二胺（44-MDA）的从头算研究

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摘要

The most commonly applied industrial synthesis of 4,4′-methylene diphenyl diamine (4,4′-MDA), an important polyurethane intermediate, is the reaction of aniline and formaldehyde. Molecular understanding of the 4,4′-MDA formation can provide strategy to prevent from side reactions. In this work, a molecular mechanism consisted of eight consecutive, elementary reaction steps from anilines and formaldehyde to the formation of 4,4′-MDA in acidic media is proposed using accurate G3MP2B3 composite quantum chemical method. Then G3MP2B3-SMD results in aqueous and aniline solutions were compared to the gas phase mechanism. Based on the gas phase calculations standard enthalpy of formation, entropy and heat capacity values were evaluated using G3MP2B3 results for intermediates The proposed mechanism was critically evaluated and important side reactions are considered: the competition of formation of protonated p-aminobenzylaniline (PABAH+), protonated aminal (AMH+) and o-aminobenzylaniline (OABAH+). Competing reactions of the 4,4′-MDA formation is also thermodynamically analyzed such as the formation of 2,4-MDAH+, 3,4-MDAH+. AMH+ can be formed through loose transition state, but it becomes kinetic dead-end, while formation of significant amount of 2,4-MDA is plausible through low-lying transition state. The acid strength of the key intermediates such as N-methylenebenzeneanilium, PABAH+, 4-methylidenecyclohexa-2,5-diene-1-iminium, and AMH+ was estimated by relative pKa calculation.
机译：重要的聚氨酯中间体4,4'-亚甲基二苯基二胺（4,4'-MDA）最常用的工业合成是苯胺和甲醛的反应。对4,4'-MDA形成的分子了解可以提供防止副反应的策略。在这项工作中，使用精确的G3MP2B3复合量子化学方法，提出了从苯胺和甲醛到在酸性介质中形成4,4'-MDA的八个连续基本反应步骤组成的分子机理。然后将G3MP2B3-SMD在水溶液和苯胺溶液中的结果与气相机理进行了比较。根据气相计算的标准生成焓，使用中间体的G3MP2B3结果评估了熵和热容值。对提出的机理进行了严格评估，并考虑了重要的副反应：质子化对氨基苄基苯胺的形成竞争（PABAH + ），质子化的氨基（AMH + ）和邻氨基苄基苯胺（OABAH + ）。还对4,4'-MDA形成的竞争反应进行了热力学分析，例如2,4-MDAH + ，3,4-MDAH + 的形成。 AMH + 可以通过松散的过渡态形成，但会变成动力学死角，而通过低洼的过渡态可能形成大量的2,4-MDA。通过以下方法估算了关键中间体的酸强度，例如N-亚甲基苯铵，PABAH + ，4-亚甲基环己基-2,5-二烯-1-亚胺和AMH + 相对pKa计算。

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