University of Oulu

Enders, L., Casadio, D. S., Aikonen, S., Lenarda, A., Wirtanen, T., Hu, T., Hietala, S., Ribeiro, L. S., Pereira, M. F. R., & Helaja, J. (2021). Air oxidized activated carbon catalyst for aerobic oxidative aromatizations of N-heterocycles. Catalysis Science & Technology, 11(17), 5962–5972. https://doi.org/10.1039/d1cy00878a

Air oxidized activated carbon catalyst for aerobic oxidative aromatizations of N-heterocycles

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Author: Enders, Lukas1; Casadio, David S.1; Aikonen, Santeri1;
Organizations: 1Department of Chemistry, University of Helsinki, A. I. Virtasen aukio 1, P.O. Box 55, 00014 Finland
2Research Unit of Sustainable Chemistry, Faculty of Technology, University of Oulu, 90014 Oulu, Finland
3Laboratory of Separation and Reaction Engineering-Laboratory of Catalysis and Materials (LSRE‐LCM), Faculty of Engineering, University of Porto, 4200‐465 Porto, Portugal
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 3 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe2021091346058
Language: English
Published: Royal Society of Chemistry, 2021
Publish Date: 2021-09-13
Description:

Abstract

A simple “reagent-free” thermal air treatment turns active carbon into a mildly oxidized material with increased quinoidic content that catalytically dehydrogenates saturated N-heterocycles to the corresponding aromatic compounds. Thermal decarboxylation improves the activity of the catalyst further, making it overall more efficient compared to other widely used carbocatalysts such as oxidized carbon nanotubes, graphene oxide and untreated active carbons. The substrate scope covers 1,2,3,4-tetrahydroquinolines (THQ), 1,2,3,4-tetrahydro-β-carbolines and related N-heterocyclic structures. The developed protocol also successfully dehydrogenates 3-(cyclohexenyl)indoles to 3-aryl indoles, opening a concise transition metal-free approach to (hetero)biaryls as exemplified with the synthesis of the core structure of progesterone receptor antagonist. Hammett plots, deuterium KIE measurements and computations at DFT level suggest that bimolecular hydride transfer mechanism is more likely to operate between THQs and the o-quinoidic sites of the catalyst, than the addition–elimination hemiaminal route. Comparison of structural parameters and catalytic performance of various oxidized carbon materials, prepared by different oxidative and optional post treatments, revealed that quinoidic content and surface area correlate with the obtained yields, while carboxylic acid content has a clear inhibiting effect for the studied oxidative dehydrogenations (ODHs). The carbocatalyst itself can be prepared from inexpensive and environmentally benign starting materials and its catalytic activity can be enhanced by a simple thermal oxidation in air that produces no reagent waste. Furthermore, oxygen is used as terminal oxidant, and the carbocatalyst is recyclable at least six times without a notable loss of activity.

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Series: Catalysis science & technology
ISSN: 2044-4753
ISSN-E: 2044-4761
ISSN-L: 2044-4753
Volume: 11
Pages: 5962 - 5972
DOI: 10.1039/D1CY00878A
OADOI: https://oadoi.org/10.1039/D1CY00878A
Type of Publication: A1 Journal article – refereed
Field of Science: 116 Chemical sciences
Subjects:
Funding: Financial support from Academy of Finland [project no. 129062 (J. H.)] is acknowledged. The Portuguese contribution was financially supported by: Base Funding – UIDB/50020/2020 of the Associate Laboratory LSRE-LCM – funded by national funds through FCT/MCTES (PIDDAC).
Copyright information: © 2021 The Authors. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
  https://creativecommons.org/licenses/by/3.0/