Periodic Reporting for period 1 - HaloCat (Elemental Halogen-Free Reversible Construction and Deconstruction of 1,2-Dihalides via Shuttle Catalysis)
Periodo di rendicontazione: 2020-06-01 al 2022-05-31
Polyhalides are essential commodity chemicals and indispensable synthetic intermediates, while their synthesis has heavily relied on the use of elemental chlorine and bromine. However, Cl2 and Br2 are infamous for their highly toxic and corrosive properties. Thousands of reported chemical accidents during the production, transport, storage, and handling of Cl2 and Br2 call for alternative and safer approaches to alleviate their usage. Meanwhile, several previously widely used halogenated commodity chemicals, such as Lindane [gamma-hexachloro-cyclohexane (HCH)], have been classified as persistent organic pollutants (POPs) and banned from use, due to their environmental persistence and devastating effects on humans and the environment. The valorization of end-of-life halogenated products has been a long sought-after goal in sustainable chemistry. This MSCA project, HaloCat, aims to develop a practical and sustainable approach to reversibly shuttle the corrosive and toxic entities (e.g. Cl2, Br2, RSCl and RSBr) between two molecules. On the one hand, it will alleviate the use of corrosive and toxic elemental chlorine and bromine in synthesis, enhancing the safety of chemical processes. On the other hand, it will provide a sustainable way to recycle persistent organic pollutants (POPs), contributing to a sustainable future.
The work carried out during the MSC Action can be divided into two parts:
(1) Electrochemistry-enabled reversible shuttle dihalogenation reactions (published in Science 2021, 371, 507–514)
The researcher has successfully developed an electrochemistry-enabled shuttle (e-shuttle) process to transfer the Cl2 and Br2 entities between 1,2-dihalides and alkenes reversibly, similar to an airport shuttle bus transports passengers back and forth between two terminals. Driven by renewable and sustainable electricity, this enabling method replaces the corrosive and toxic elemental chlorine and bromine in synthesizing vicinal dichlorides and dibromides, enhancing the safety of chemical processes. Meanwhile, it also renders the synthesis of fine chemicals from the remediation of the Lindane contaminated soils without any pre-treatment. When Lindane was subjected to our standard e-shuttle conditions with alkenes as acceptors, Lindane successfully transferred its six chlorine atoms to the acceptor alkene to form benzene, the fully dechlorinated byproduct of Lindane, alongside a synthetically valuable dichloride product, through three successive retro-dichlorination events. We believe that this research work opens up new opportunities to replace the traditional linear "take-make-dispose" approach with a circular process in handling end-of-life chemical pollutants, contributing to protecting the environment and securing a sustainable future.
Since its publication, this research work has attracted media coverage regarding its exceptional novelty, sustainability, and promising application in environmental protection. The positive feedback came not only from the chemistry community but also from the general public media, such as Frankfurter Allgemeine, Nat. Catal., C&EN News, ChemistryViews, ETH news, JGU news, and Chem Europe.
(2) Electrochemistry-enabled shuttle hetero-difunctionalization reactions (manuscript submitted for publication)
The researcher developed an electrochemistry-enabled shuttle strategy to transfer two distinct functional groups, a sulfide and a halide, between β-halosulfide and alkynes with excellent chemo-, regio-, and stereoselectivity, unlocking a rare example of shuttle hetero-difunctionalization reaction. The paired electrolysis process, which is considered a holy grail by the electrochemistry community, was successfully employed to deconstruct and reconstruct two different inert chemical bonds sequentially. More importantly, the selective anodic oxidation of one anion over the other, by taking advantage of differences in redox potentials, serves as the critical design to achieve unprecedented chemoselectivity. This easily scalable methodology enables the construction of a myriad of densely functionalized β-halo alkenyl sulfides in unprecedented chemo-, regio-, and stereoselectivity using benign surrogates, e.g. 2-bromoethyl sulfide, avoiding the handling of corrosive and oxidative RS–Br reagents. Moreover, the researcher also successfully performed the defunctionalization reaction of β-bromosulfide compounds to their corresponding alkenes without releasing the toxic sulfenyl bromide reagents, taking advantage of the reversibility of the shuttle process.
(1) Electrochemistry-enabled reversible shuttle dihalogenation reactions (published in Science 2021, 371, 507–514)
The researcher has successfully developed an electrochemistry-enabled shuttle (e-shuttle) process to transfer the Cl2 and Br2 entities between 1,2-dihalides and alkenes reversibly, similar to an airport shuttle bus transports passengers back and forth between two terminals. Driven by renewable and sustainable electricity, this enabling method replaces the corrosive and toxic elemental chlorine and bromine in synthesizing vicinal dichlorides and dibromides, enhancing the safety of chemical processes. Meanwhile, it also renders the synthesis of fine chemicals from the remediation of the Lindane contaminated soils without any pre-treatment. When Lindane was subjected to our standard e-shuttle conditions with alkenes as acceptors, Lindane successfully transferred its six chlorine atoms to the acceptor alkene to form benzene, the fully dechlorinated byproduct of Lindane, alongside a synthetically valuable dichloride product, through three successive retro-dichlorination events. We believe that this research work opens up new opportunities to replace the traditional linear "take-make-dispose" approach with a circular process in handling end-of-life chemical pollutants, contributing to protecting the environment and securing a sustainable future.
Since its publication, this research work has attracted media coverage regarding its exceptional novelty, sustainability, and promising application in environmental protection. The positive feedback came not only from the chemistry community but also from the general public media, such as Frankfurter Allgemeine, Nat. Catal., C&EN News, ChemistryViews, ETH news, JGU news, and Chem Europe.
(2) Electrochemistry-enabled shuttle hetero-difunctionalization reactions (manuscript submitted for publication)
The researcher developed an electrochemistry-enabled shuttle strategy to transfer two distinct functional groups, a sulfide and a halide, between β-halosulfide and alkynes with excellent chemo-, regio-, and stereoselectivity, unlocking a rare example of shuttle hetero-difunctionalization reaction. The paired electrolysis process, which is considered a holy grail by the electrochemistry community, was successfully employed to deconstruct and reconstruct two different inert chemical bonds sequentially. More importantly, the selective anodic oxidation of one anion over the other, by taking advantage of differences in redox potentials, serves as the critical design to achieve unprecedented chemoselectivity. This easily scalable methodology enables the construction of a myriad of densely functionalized β-halo alkenyl sulfides in unprecedented chemo-, regio-, and stereoselectivity using benign surrogates, e.g. 2-bromoethyl sulfide, avoiding the handling of corrosive and oxidative RS–Br reagents. Moreover, the researcher also successfully performed the defunctionalization reaction of β-bromosulfide compounds to their corresponding alkenes without releasing the toxic sulfenyl bromide reagents, taking advantage of the reversibility of the shuttle process.
Chlorine and bromine are notorious among scientists and the general public as very toxic chemical reagents that have a long history as poisons or as chemical weapons. The new methodology developed during this fellowship eludes the need to use or get exposed to highly toxic chlorine or bromine in a process of both industrial and laboratory scale importance. These results thus have universal implications beyond synthetic chemistry due to the historical, environmental, health, and political impact of chlorine/bromine.
The reaction's reversibility enabled the researcher to use soil samples contaminated with Lindane as reagents to valorize simple organic building blocks in a unique example of combining a recycling process with a synthetically relevant reaction. In light of the environmental importance of chemical recycling, our reversible e-shuttle strategy provided an ideal platform to recycle and valorize end-of-life Lindane via retro-dihalogenations, enabling a circular economy of halogenated chemicals and contributing to environmental protection.
The process we developed merges two different research areas, electrochemistry and transfer reactions, in an interdisciplinary approach. This approach addresses significant challenges in both research areas, clearly demonstrating the symbiotic nature of this novel strategy. This research should thus broadly impact the organic chemistry, electrochemistry, catalysis, and industrial chemistry communities.
The reaction's reversibility enabled the researcher to use soil samples contaminated with Lindane as reagents to valorize simple organic building blocks in a unique example of combining a recycling process with a synthetically relevant reaction. In light of the environmental importance of chemical recycling, our reversible e-shuttle strategy provided an ideal platform to recycle and valorize end-of-life Lindane via retro-dihalogenations, enabling a circular economy of halogenated chemicals and contributing to environmental protection.
The process we developed merges two different research areas, electrochemistry and transfer reactions, in an interdisciplinary approach. This approach addresses significant challenges in both research areas, clearly demonstrating the symbiotic nature of this novel strategy. This research should thus broadly impact the organic chemistry, electrochemistry, catalysis, and industrial chemistry communities.