Cha Shuangshuang, Chen Yuxin, Du Wei, Wu Jianxiang, Wang Ran, Jiang Tao, Yang Xuejing, Lian Cheng, Liu Honglai, Gong Ming
Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Fudan University, Shanghai 200438, China.
State Key Laboratory of Chemical Engineering, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, China.
JACS Au. 2024 Sep 5;4(9):3629-3640. doi: 10.1021/jacsau.4c00585. eCollection 2024 Sep 23.
Degradable polymers are an effective solution for white plastic pollution. Polycaprolactone is a type of degradable plastic with desirable mechanical and biocompatible properties, and its monomer, ε-caprolactone (ε-CL), is often synthesized by Baeyer-Villiger (B-V) oxidation that demands peroxyacids with low safety and low atom-efficiency. Herein, we devised an electrochemical B-V oxidation system simply driven by HO for the efficient production of ε-CL. This system involves two steps with the direct oxidation of HO into •OOH radicals at the electrode surface and the indirect oxidation of cyclohexanone by the generated reactive oxygen species. The modulation of the interfacial ionic environment by amphipathic sulfonimide anions [e.g., bis(trifluoromethane)sulfonimide (TFSI)] is highly critical. It enables the efficient B-V oxidation into ε-caprolactone with ∼100% selectivity and 68.4% yield at a potential of 1.28 V vs RHE, much lower than the potentials applied for electrochemical B-V oxidation systems using water as the O sources. On hydrophilic electrodes with the action of sulfonimide anions, hydrophilic HO can be enriched within the double layer for direct oxidation while hydrophobic cyclohexanone can be simultaneously accumulated for rapidly reacting with the reactive oxygen species. This work not only enriches the electrified method of the ancient B-V oxidation by using only HO toward monomer production of biodegradable plastics but also emphasizes the critical role of the interfacial ionic environment for electrosynthesis systems that may extend the scope of activity optimization.
可降解聚合物是解决白色塑料污染的有效方案。聚己内酯是一种具有理想机械性能和生物相容性的可降解塑料，其单体ε-己内酯（ε-CL）通常通过拜耳-维利格（B-V）氧化法合成，该方法需要使用安全性低且原子效率低的过氧酸。在此，我们设计了一种仅由HO驱动的电化学B-V氧化系统，用于高效生产ε-CL。该系统包括两个步骤，首先在电极表面将HO直接氧化为•OOH自由基，然后通过生成的活性氧物种间接氧化环己酮。两亲性磺酰亚胺阴离子[例如双（三氟甲烷）磺酰亚胺（TFSI）]对界面离子环境的调节至关重要。它能够在相对于可逆氢电极（RHE）为1.28 V的电位下，以约100%的选择性和68.4%的产率将B-V高效氧化为ε-己内酯，这比使用水作为氧源的电化学B-V氧化系统所施加的电位低得多。在磺酰亚胺阴离子作用下的亲水电极上，亲水性的HO可以在双电层内富集以进行直接氧化，而疏水性的环己酮可以同时积累以便与活性氧物种快速反应。这项工作不仅通过仅使用HO丰富了古老的B-V氧化的电化方法，用于可生物降解塑料的单体生产，而且强调了界面离子环境对电合成系统的关键作用，这可能会扩展活性优化的范围。
