Yang Mingze, Lenarda Anna, Frindy Sana, Sang Yushuai, Oksanen Valtteri, Bolognani Adriano, Hendrickx Lisa, Helaja Juho, Li Yongdan
Department of Chemical and Metallurgical Engineering, School of Chemical Engineering, Aalto University, Espoo 02150, Finland.
Department of Chemistry, University of Helsinki, Helsinki 00014, Finland.
Proc Natl Acad Sci U S A. 2023 Aug;120(31):e2303564120. doi: 10.1073/pnas.2303564120. Epub 2023 Jul 24.
A metal-free route based on a carbon catalyst to synthesize biphenyls through oxidative dehydrogenation (ODH) of phenyl cyclohexene has been investigated. Among the samples examined, an air-oxidized active carbon exhibits the best activity with a 9.1 × 10 h rate constant, yielding 74% biphenyl in 28 h at 140 °C under five bar O in anisole. The apparent activation energy is measured as 54.5 kJ⋅mol. The extended reaction scope, consisting of 15 differently substituted phenyl cyclohexenes, shows the wide applicability of the proposed method. The catalyst's good recyclability over six runs suggests this ODH method as a promising route to access the biaryl compounds. In addition, the reaction mechanism is investigated with a combination of X-ray photoelectron spectroscopy, functional group blocking, and model compounds of carbon catalysts and is proposed to be based on the redox cycle of the quinoidic groups on the carbon surface. Additional experiments prove that the addition of the catalytic amount of acid (methanesulfonic acid) accelerates the reaction. In addition, Hammett plot examination suggests the formation of a carbonium intermediate, and its possible structure is outlined.
研究了一种基于碳催化剂的无金属路线，通过苯环己烯的氧化脱氢（ODH）合成联苯。在所考察的样品中，空气氧化的活性炭表现出最佳活性，速率常数为9.1×10 h，在140℃、五巴氧气压力下于苯甲醚中反应28小时，联苯产率为74%。测得表观活化能为54.5 kJ⋅mol。由15种不同取代的苯环己烯组成的扩展反应范围表明了该方法的广泛适用性。该催化剂在六次循环中具有良好的可回收性，表明这种ODH方法是获得联芳基化合物的一条有前景的途径。此外，结合X射线光电子能谱、官能团阻断以及碳催化剂的模型化合物对反应机理进行了研究，并提出其基于碳表面醌型基团的氧化还原循环。额外的实验证明，加入催化量的酸（甲磺酸）可加速反应。此外，哈米特图分析表明形成了碳正离子中间体，并概述了其可能的结构。
