Department of Chemistry, Indian Institute of Science Education and Research Tirupati, Tirupati 517507, India.
Department of Applied Sciences, University Institute of Engineering and Technology, Panjab University, Chandigarh 160014, India.
J Am Chem Soc. 2022 Mar 2;144(8):3347-3352. doi: 10.1021/jacs.1c12644. Epub 2022 Feb 18.
Over the last 50 years, proposals of α-carbonyl cation intermediates have been driven by chemical intuition and indirect evidence. Recently, wide interest in α-carbonyl cation chemistry has opened new gates to prepare α-functionalized carbonyl compounds. Though these intrinsically unstable carbocations are formed under forcing conditions (e.g., in a strong acid medium), their fleeting existence prohibits direct observation or spectroscopic measurement. We report that high-speed aqueous microdroplets can directly capture α-carbonyl cation intermediates from various reactions (Friedel-Crafts arylation, deoxygenation, and azidation) upon bombarding with the corresponding reaction aliquots. The α-carbonyl cations caged in water droplets are then desorbed to the gas phase, allowing their successful measurement by mass spectrometry. This has also enabled us to simultaneously monitor the relative abundance of the associated precursor, α-carbonyl cation intermediate, and product during the progress of the reaction.
在过去的 50 年中，α-羰基阳离子中间体的提议受到化学直觉和间接证据的推动。最近，人们对α-羰基阳离子化学产生了广泛的兴趣，为制备α-官能化羰基化合物开辟了新的途径。尽管这些本质上不稳定的碳正离子是在强制条件下形成的（例如，在强酸介质中），但它们短暂的存在阻止了直接观察或光谱测量。我们报告说，高速水微滴可以通过用相应的反应等分试样撞击，直接从各种反应（Friedel-Crafts 芳基化、脱氧和叠氮化）中捕获α-羰基阳离子中间体。然后，被笼在水滴中的α-羰基阳离子解吸到气相中，允许通过质谱法成功测量。这也使我们能够在反应过程中同时监测相关前体、α-羰基阳离子中间体和产物的相对丰度。
