Yu Jiaying, Mateos Javier, Carraro Mauro
Department of Chemical Sciences, University of Padova, Via F. Marzolo 1, 35131 Padova, Italy.
College of Chemistry and Environmental Engineering, Shenzhen University, 3688 Nanhai Ave, Shenzhen 518060, China.
Nanomaterials (Basel). 2023 Jan 18;13(3):394. doi: 10.3390/nano13030394.
Halloysite nanotubes can be used for the preparation of solid catalysts. Owing to their natural availability at low-cost as well as to their large and easy-to-functionalize surface, they can be conveniently activated with mineral acids or derivatized with acidic groups. Nevertheless, the use of HNTs as catalysts in complex transformations is still limited. Herein, we report two strategies to utilize HNT-based materials as solid acidic catalysts for the Biginelli reaction. To this aim, two methods for increasing the number of acidic sites on the HNTs were explored: (i) the treatment with piranha solution (Pir-HNTs) and (ii) the functionalization with phenylboronic acid (in particular with benzene-1,4-diboronic acid: the sample is denoted as HNT-BOA). Interestingly, both strategies enhance the performance of the multicomponent reaction. Pir-HNTs and HNT-BOA show an increased reactivity (72% and 89% yield, respectively) in comparison with pristine HNTs (52%). Additionally, Pir-HNTs can be reused up to five times without significant performance loss. Moreover, the method also displays good reaction scope, as demonstrated by the preparation of 12 different 3,4-dihydropyrimidinones in up to 71% yield. Therefore, the described strategies are promising for enhancing the acidity of the HNTs as catalysts for the organic reaction.
埃洛石纳米管可用于制备固体催化剂。由于其成本低廉且易于获得，以及其表面大且易于功能化，它们可以方便地用无机酸活化或用酸性基团衍生化。然而，在复杂转化中使用埃洛石纳米管作为催化剂仍然受到限制。在此，我们报告了两种利用基于埃洛石纳米管的材料作为Biginelli反应的固体酸性催化剂的策略。为此，探索了两种增加埃洛石纳米管上酸性位点数量的方法：（i）用王水（Pir-HNTs）处理和（ii）用苯硼酸（特别是用苯-1,4-二硼酸：该样品表示为HNT-BOA）进行功能化。有趣的是，这两种策略都提高了多组分反应的性能。与原始埃洛石纳米管（52%）相比，Pir-HNTs和HNT-BOA的反应活性有所提高（产率分别为72%和89%）。此外，Pir-HNTs可以重复使用多达五次而不会有明显的性能损失。此外，该方法还显示出良好的反应范围，通过制备12种不同的3,4-二氢嘧啶酮，产率高达71%得到了证明。因此，所描述的策略有望提高埃洛石纳米管作为有机反应催化剂的酸度。
