Guo Yunfei, Muuronen Mikko, Deglmann Peter, Lucas Frederic, Sijbesma Rint P, Tomović Željko
Polymer Performance Materials Group, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
BASF SE, Carl-Bosch-Straße 38, 67056 Ludwigshafen am Rhein, Germany.
J Org Chem. 2021 Apr 16;86(8):5651-5659. doi: 10.1021/acs.joc.1c00119. Epub 2021 Apr 1.
The formation of isocyanurates via cyclotrimerization of aromatic isocyanates is widely used to enhance the physical properties of a variety of polyurethanes. The most commonly used catalysts in industries are carboxylates for which the exact catalytically active species have remained controversial. We investigated how acetate and other carboxylates react with aromatic isocyanates in a stepwise manner and identified that the carboxylates are only precatalysts in the reaction. The reaction of carboxylates with an excess of aromatic isocyanates leads to irreversible formation of corresponding deprotonated amide species that are strongly nucleophilic and basic. As a result, they are active catalysts during the nucleophilic anionic trimerization, but can also deprotonate urethane and urea species present, which in turn catalyze the isocyanurate formation. The current study also shows how quantum chemical calculations can be used to direct spectroscopic identification of reactive intermediates formed during the active catalytic cycle with predictive accuracy.
通过芳香族异氰酸酯的环三聚反应形成异氰脲酸酯被广泛用于增强各种聚氨酯的物理性能。工业上最常用的催化剂是羧酸盐，但其确切的催化活性物种一直存在争议。我们研究了乙酸盐和其他羧酸盐如何与芳香族异氰酸酯逐步反应，并确定羧酸盐在该反应中只是预催化剂。羧酸盐与过量的芳香族异氰酸酯反应会导致相应的去质子化酰胺物种不可逆地形成，这些物种具有很强的亲核性和碱性。因此，它们在亲核阴离子三聚反应中是活性催化剂，但也会使存在的聚氨酯和脲物种去质子化，进而催化异氰脲酸酯的形成。当前的研究还展示了如何利用量子化学计算以预测精度指导对活性催化循环中形成的反应中间体进行光谱鉴定。
