Effect of hydrogen bonding on the kinetics of the urethane reaction
Effect of hydrogen bonding on the kinetics of the urethane reaction
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DOI：
10.1021/j100849a013
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发表时间：
1968-03
期刊：
影响因子：
--
通讯作者：
A. Oberth;R. S. Bruenner
中科院分区：
文献类型：
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作者：
A. Oberth;R. S. Bruenner
结果表明，非催化脲烷反应的速率主要取决于聚合（自结合）醇的浓度。溶剂通过分解聚合物，使反应速率减慢，其大小与溶剂的氢键能力直接相关。聚合醇的高反应性归因于聚合物中H-0键的极化（减弱）。由H-0吸收带向较低频率移动所表明的极化程度，在胺-醇配合物中更为明显，因此，它是氨基甲酸乙酯反应的强催化剂。红外研究表明，胺醇络合物的形成及其催化活性不仅与胺的碱度有关，还与位阻因素有关。例如，二烷基苯胺不会形成氢键醇胺配合物，也不会催化反应，而碱度大致相等的吡啶却会形成配合物，也会加速反应。在动力学数据的基础上，结合红外光谱研究，提出了一种合理考虑溶剂和胺对反应速率影响的反应机理。提出了氨基甲酸乙酯反应的速率决定步骤是醇异氰酸酯络合物对氨基甲酸乙酯的重排。反应的动力学描述以计算反应混合物中醇异氰酸酯络合物的浓度为中心。这样的计算可以合理地描述整个反应物浓度范围内的聚氨酯反应。
It is shown that the rate of the uncatalyzed urethane reaction depends essentially on the concentration of the polymeric (self-associated) alcohol. Solvents, by breaking down the polymer, cause a retardation of the reaction rate, the magnitude of which can be related directly to the hydrogen-bonding power of the solvent. The high reactivity of the polymeric alcohol is attributed to the polarization (weakening) of the H-0 bond in the polymer. The degree of polarization, as indicated by the shift of the H-0 absorption band to lower frequencies, is even more pronounced in amine-alcohol complexes, which, accordingly, are strong catalysts for the urethane reaction. Infrared studies have shown that the formation of the amine-alcohol complex and hence the catalytic activity depends not only on the basicity of the amine but also on steric factors. Dialkyl-anilines, eg, do not form hydrogen-bonded alcohol-amine complexes and do not catalyze the reaction, while pyridine, of approximately equal basicity, does form a complex and also accelerates the reaction. Based on kinetic data, combined with ir studies, a reaction mechanism is proposed which properly accounts for the effect of solvents and amines on the reaction rate. It is proposed that the rate-determining step in the urethane reaction is the rearrangement of the alcohol-isocyanate complex to the urethane. The kinetic description of the reaction centers in the calculation of the concentration of the alcohol-isocyanate complex in the reaction mixture. Such calculations are shown to reasonably portray the urethane reaction over the whole range of re-actant concentrations.