Bartalucci Ettore, Schumacher Christian, Hendrickx Leeroy, Puccetti Francesco, d'Anciães Almeida Silva Igor, Dervişoğlu Rıza, Puttreddy Rakesh, Bolm Carsten, Wiegand Thomas
Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470, Mülheim/Ruhr, Germany.
Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, 52074, Aachen, Germany.
Chemistry. 2023 Feb 24;29(12):e202203466. doi: 10.1002/chem.202203466. Epub 2023 Jan 20.
Mechanical forces, including compressive stresses, have a significant impact on chemical reactions. Besides the preparative opportunities, mechanochemical conditions benefit from the absence of any organic solvent, the possibility of a significant synthetic acceleration and unique reaction pathways. Together with an accurate characterization of ball-milling products, the development of a deeper mechanistic understanding of the occurring transformations at a molecular level is critical for fully grasping the potential of organic mechanosynthesis. We herein studied a bromination of a cyclic sulfoximine in a mixer mill and used solid-state nuclear magnetic resonance (NMR) spectroscopy for structural characterization of the reaction products. Magic-angle spinning (MAS) was applied for elucidating the product mixtures taken from the milling jar without introducing any further post-processing on the sample. Ex situ C-detected NMR spectra of ball-milling products showed the formation of a crystalline solid phase with the regioselective bromination of the S-aryl group of the heterocycle in position 4. Completion is reached in less than 30 minutes as deduced from the NMR spectra. The bromination can also be achieved by magnetic stirring, but then, a longer reaction time is required. Mixing the solid educts in the NMR rotor allows to get in situ insights into the reaction and enables the detection of a reaction intermediate. The pressure alone induced in the rotor by MAS is not sufficient to lead to full conversion and the reaction occurs on slower time scales than in the ball mill, which is crucial for analysing mixtures taken from the milling jar by solid-state NMR. Our data suggest that on top of centrifugal forces, an efficient mixing of the starting materials is required for reaching a complete reaction.
机械力，包括压应力，对化学反应有重大影响。除了制备机会外，机械化学条件还得益于无需任何有机溶剂、显著加速合成的可能性以及独特的反应途径。与球磨产物的精确表征相结合，在分子水平上深入理解所发生转化的机理对于充分掌握有机机械合成的潜力至关重要。我们在此研究了在混合研磨机中对环状亚砜亚胺进行溴化反应，并使用固态核磁共振（NMR）光谱对反应产物进行结构表征。采用魔角旋转（MAS）来阐明从研磨罐中取出的产物混合物，而无需对样品进行任何进一步的后处理。球磨产物的异位碳检测NMR光谱显示形成了一种结晶固相，杂环的S - 芳基在4位发生了区域选择性溴化。从NMR光谱推断，反应在不到30分钟内完成。溴化反应也可以通过磁力搅拌实现，但那样需要更长的反应时间。在NMR转子中混合固体反应物能够对反应进行原位洞察，并能够检测到反应中间体。仅由MAS在转子中产生的压力不足以导致完全转化，并且反应发生的时间尺度比在球磨机中慢，这对于通过固态NMR分析从研磨罐中取出的混合物至关重要。我们的数据表明，除了离心力之外，还需要对起始原料进行有效混合才能实现完全反应。
