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The Concept of Chemical Generators: On-Site On-Demand Production of Hazardous Reagents in Continuous Flow

[Image: see text] In recent years, a steadily growing number of chemists, from both academia and industry, have dedicated their research to the development of continuous flow processes performed in milli- or microreactors. The common availability of continuous flow equipment at virtually all scales...

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Autores principales: Dallinger, Doris, Gutmann, Bernhard, Kappe, C. Oliver
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2020
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7467564/
https://www.ncbi.nlm.nih.gov/pubmed/32543830
http://dx.doi.org/10.1021/acs.accounts.0c00199
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author Dallinger, Doris
Gutmann, Bernhard
Kappe, C. Oliver
author_facet Dallinger, Doris
Gutmann, Bernhard
Kappe, C. Oliver
author_sort Dallinger, Doris
collection PubMed
description [Image: see text] In recent years, a steadily growing number of chemists, from both academia and industry, have dedicated their research to the development of continuous flow processes performed in milli- or microreactors. The common availability of continuous flow equipment at virtually all scales and affordable cost has additionally impacted this trend. Furthermore, regulatory agencies such as the United States Food and Drug Administration actively encourage continuous manufacturing of active pharmaceutical ingredients (APIs) with the vision of quality and productivity improvements. That is why the pharmaceutical industry is progressively implementing continuous flow technologies. As a result of the exceptional characteristics of continuous flow reactors such as small reactor volumes and remarkably fast heat and mass transfer, process conditions which need to be avoided in conventional batch syntheses can be safely employed. Thus, continuous operation is particularly advantageous for reactions at high temperatures/pressures (novel process windows) and for ultrafast, exothermic reactions (flash chemistry). In addition to conditions that are outside of the operation range of conventional stirred tank reactors, reagents possessing a high hazard potential and therefore not amenable to batch processing can be safely utilized (forbidden chemistry). Because of the small reactor volumes, risks in case of a failure are minimized. Such hazardous reagents often are low molecular weight compounds, leading generally to the most atom-, time-, and cost-efficient route toward the desired product. Ideally, they are generated from benign, readily available and cheap precursors within the closed environment of the flow reactor on-site on-demand. By doing so, the transport, storage, and handling of those compounds, which impose a certain safety risk especially on a large scale, are circumvented. This strategy also positively impacts the global supply chain dependency, which can be a severe issue, particularly in times of stricter safety regulations or an epidemic. The concept of the in situ production of a hazardous material is generally referred to as the “generator” of the material. Importantly, in an integrated flow process, multiple modules can be assembled consecutively, allowing not only an in-line purification/separation and quenching of the reagent, but also its downstream conversion to a nonhazardous product. For the past decade, research in our group has focused on the continuous generation of hazardous reagents using a range of reactor designs and experimental techniques, particularly toward the synthesis of APIs. In this Account, we therefore introduce chemical generator concepts that have been developed in our laboratories for the production of toxic, explosive, and short-lived reagents. We have defined three different classes of generators depending on the reactivity/stability of the reagents, featuring reagents such as Br(2), HCN, peracids, diazomethane (CH(2)N(2)), or hydrazoic acid (HN(3)). The various reactor designs, including in-line membrane separation techniques and real-time process analytical technologies for the generation, purification, and monitoring of those hazardous reagents, and also their downstream transformations are presented. This Account should serve as food for thought to extend the scope of chemical generators for accomplishing more efficient and more economic processes.
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spelling pubmed-74675642020-09-03 The Concept of Chemical Generators: On-Site On-Demand Production of Hazardous Reagents in Continuous Flow Dallinger, Doris Gutmann, Bernhard Kappe, C. Oliver Acc Chem Res [Image: see text] In recent years, a steadily growing number of chemists, from both academia and industry, have dedicated their research to the development of continuous flow processes performed in milli- or microreactors. The common availability of continuous flow equipment at virtually all scales and affordable cost has additionally impacted this trend. Furthermore, regulatory agencies such as the United States Food and Drug Administration actively encourage continuous manufacturing of active pharmaceutical ingredients (APIs) with the vision of quality and productivity improvements. That is why the pharmaceutical industry is progressively implementing continuous flow technologies. As a result of the exceptional characteristics of continuous flow reactors such as small reactor volumes and remarkably fast heat and mass transfer, process conditions which need to be avoided in conventional batch syntheses can be safely employed. Thus, continuous operation is particularly advantageous for reactions at high temperatures/pressures (novel process windows) and for ultrafast, exothermic reactions (flash chemistry). In addition to conditions that are outside of the operation range of conventional stirred tank reactors, reagents possessing a high hazard potential and therefore not amenable to batch processing can be safely utilized (forbidden chemistry). Because of the small reactor volumes, risks in case of a failure are minimized. Such hazardous reagents often are low molecular weight compounds, leading generally to the most atom-, time-, and cost-efficient route toward the desired product. Ideally, they are generated from benign, readily available and cheap precursors within the closed environment of the flow reactor on-site on-demand. By doing so, the transport, storage, and handling of those compounds, which impose a certain safety risk especially on a large scale, are circumvented. This strategy also positively impacts the global supply chain dependency, which can be a severe issue, particularly in times of stricter safety regulations or an epidemic. The concept of the in situ production of a hazardous material is generally referred to as the “generator” of the material. Importantly, in an integrated flow process, multiple modules can be assembled consecutively, allowing not only an in-line purification/separation and quenching of the reagent, but also its downstream conversion to a nonhazardous product. For the past decade, research in our group has focused on the continuous generation of hazardous reagents using a range of reactor designs and experimental techniques, particularly toward the synthesis of APIs. In this Account, we therefore introduce chemical generator concepts that have been developed in our laboratories for the production of toxic, explosive, and short-lived reagents. We have defined three different classes of generators depending on the reactivity/stability of the reagents, featuring reagents such as Br(2), HCN, peracids, diazomethane (CH(2)N(2)), or hydrazoic acid (HN(3)). The various reactor designs, including in-line membrane separation techniques and real-time process analytical technologies for the generation, purification, and monitoring of those hazardous reagents, and also their downstream transformations are presented. This Account should serve as food for thought to extend the scope of chemical generators for accomplishing more efficient and more economic processes. American Chemical Society 2020-06-16 2020-07-21 /pmc/articles/PMC7467564/ /pubmed/32543830 http://dx.doi.org/10.1021/acs.accounts.0c00199 Text en Copyright © 2020 American Chemical Society This is an open access article published under a Creative Commons Attribution (CC-BY) License (http://pubs.acs.org/page/policy/authorchoice_ccby_termsofuse.html) , which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
spellingShingle Dallinger, Doris
Gutmann, Bernhard
Kappe, C. Oliver
The Concept of Chemical Generators: On-Site On-Demand Production of Hazardous Reagents in Continuous Flow
title The Concept of Chemical Generators: On-Site On-Demand Production of Hazardous Reagents in Continuous Flow
title_full The Concept of Chemical Generators: On-Site On-Demand Production of Hazardous Reagents in Continuous Flow
title_fullStr The Concept of Chemical Generators: On-Site On-Demand Production of Hazardous Reagents in Continuous Flow
title_full_unstemmed The Concept of Chemical Generators: On-Site On-Demand Production of Hazardous Reagents in Continuous Flow
title_short The Concept of Chemical Generators: On-Site On-Demand Production of Hazardous Reagents in Continuous Flow
title_sort concept of chemical generators: on-site on-demand production of hazardous reagents in continuous flow
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7467564/
https://www.ncbi.nlm.nih.gov/pubmed/32543830
http://dx.doi.org/10.1021/acs.accounts.0c00199
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