Modulating the catalytic behavior of non-noble metal nanoparticles by inter-particle interaction for chemoselective hydrogenation of nitroarenes into corresponding azoxy or azo compounds
作者:Lichen Liu、Patricia Concepción、Avelino Corma
DOI:10.1016/j.jcat.2018.11.011
日期:2019.1
Aromatic azoxy compounds have wide applications and they can be prepared by stoichiometric or catalytic reactions with H2O2 or N2H4 starting from anilines or nitroarenes. In this work, we will present the direct chemoselective hydrogenation of nitroarenes with H2 to give aromatic azoxy compounds under base-free mild conditions, with a bifunctional catalytic system formed by Ni nanoparticles covered
芳族乙氧基化合物具有广泛的用途,它们可以通过化学计量或催化反应与H 2 O 2或N 2 H 4从苯胺或硝基芳烃开始反应制备。在这项工作中,我们将介绍在无碱温和条件下用H 2直接对硝基芳烃进行化学选择性加氢以生成芳族氮氧基化合物的方法,该方法是由覆盖有几层碳的Ni纳米颗粒形成的双功能催化体系([受电子邮件保护] NPs )和CeO 2纳米粒子。[受电子邮件保护的] 2催化剂的催化性能超过了最新的Au / CeO 2由硝基苯直接生产production氧基苯的催化剂。借助动力学和光谱学结果,提出了一种双功能机理,其中硝基苯的氢化可以在转化率> 95%和选择性> 93%的情况下终止于乙氧基苯的生成,或者可以进一步推动硝基苯的氢化以形成偶氮苯。 > 85%的选择性。通过用非贵金属制备双官能催化剂,不仅可以实现硝基芳烃的化学选择性加氢成苯胺,而且还可以实现相应的氮氧基和偶氮化合物的化学选择性加氢。
An Easy Access to Aromatic Azo Compounds under Ultrasound/Microwave Irradiation
Chemoselective reduction of nitroarenes to azo and azoxy compounds was easily achieved using zinc powder and ammonium chloride in DMF or DMF-water (95:5) under high intensity ultrasound (US) or microwave (MW) irradiation, separately or combined. When carried out under conventional heating the reaction required much higher temperatures and gave lower yields. The addition of a small amount of water caused a dramatic increase in the reactivity, permitting the reduction of hindered nitroarenes at the expense of selectivity. A novel reactor for combined US/MW irradiation was employed which demonstrated additional beneficial effects.
The oxidation of 3-aminopyridine to 3,3′-azoxypyridine by peroxomonophosphoricacid (PMPA) is a total second order reaction: first order each in peroxomonophosphoricacid and 3-aminopyridine at constant acidity. The observed pH-rate profile has been rationalized invoking various PMPA species, protonated and unprotonated forms of 3-aminopyridine as the reactive species and their reactivities have been
demonstrated a facile methodology to construct single Nb site catalysts with merely 0.63 wt% Nb by employing α-hydroxy carboxylic acid-functionalized cotton fiber as green and sustainable supporting material. The as-synthesized catalysts have been characterized thoroughly and exhibited a superior catalytic activity for selective oxidation of aniline into azoxybenzene with nearly 100% utilization efficiency
这项工作展示了一种简便的方法,通过使用 α-羟基羧酸功能化的棉纤维作为绿色和可持续的支撑材料,构建含铌量仅为 0.63 wt% 的单 Nb 位点催化剂。合成后的催化剂已被彻底表征,并在温和和绿色条件下表现出优异的苯胺选择性氧化成偶氮基苯的催化活性,H 2 O 2的利用效率接近 100% 。值得注意的是,它展示了最高的 TOF (4806 h -1) 在目前报道的多相催化剂中。此外,该催化剂在连续流动条件下稳定运行,与这些转化中报道的间歇工艺相比具有显着优势。活性测试和催化剂表征表明原子分散的Nb-peroxo配位中心实际上是催化位点。特别是,棉纤维上的 α-羟基羧酸基团在配位/稳定单个 Nb 位点方面发挥了重要作用。此外,1H MAS NMR谱证实芳基胺与共价接枝在棉纤维上的游离α-羟基羧酸基团之间存在酸碱相互作用,有利于底物的吸附和活化。机理研究表明偶氮衍生物是通过N-苯基羟胺与亚硝基苯
Catalytic selective oxidation of aromatic amines to azoxy derivatives with an ultralow loading of peroxoniobate salts
Moreover, the reaction can proceed smoothly with stoichiometric amounts of H2O2 without external heating and additives. The salts are also highly active in the conversion of various substituted aromatic amines with excellent selectivity towards azoxy products in simple operations. Mechanistic studies utilizing butylated hydroxytoluene (BHT) as a radical scavenger proved that the reaction proceeded through
这项工作表明,酒石酸配位的过氧化铌酸盐可用作在绿色和非常温和的条件下将苯胺氧化偶联成偶氮苯的高效催化剂。这些盐通过 FT-IR 光谱、元素分析、ICP-AES、TGA、ESI-MS、93 Nb NMR、UV-vis 光谱和 EXAFS 光谱进行了全面的合成和表征。值得注意的是,使用 ppm 级过氧化铌基催化剂实现了苯胺的完全转化和对偶氮苯的出色选择性(超过 95%)。此外,反应可以在化学计量的 H 2 O 2下顺利进行无需外部加热和添加剂。这些盐在各种取代芳香胺的转化中也具有很高的活性,在简单的操作中对偶氮氧基产物具有优异的选择性。使用丁基化羟基甲苯 (BHT) 作为自由基清除剂的机理研究证明,该反应是通过催化机制而不是自由基方法进行的。此外,HRMS 和 UV-vis 表征提供了明确的证据表明 Nb-(η 2 -O 2 ) 物质是参与苯胺选择性氧化的活性中间体。-NH 2基团与盐的Nb-(η