An in-situ study of the thermal decomposition of 2,2'-azobis(2-methylpropionitrile) radical chemistry using a dual-mode EPR resonator

Magri, Giuseppina, Barter, Michael ORCID: https://orcid.org/0000-0002-4404-9397, Fletcher-Charles, Jack, Choi, Heungjae ORCID: https://orcid.org/0000-0003-1108-293X, Slocombe, Daniel ORCID: https://orcid.org/0000-0003-3590-6075, Richards, Emma ORCID: https://orcid.org/0000-0001-6691-2377, Folli, Andrea ORCID: https://orcid.org/0000-0001-8913-6606, Porch, Adrian ORCID: https://orcid.org/0000-0001-5293-8883 and Murphy, Damien M. ORCID: https://orcid.org/0000-0002-5941-4879 2023. An in-situ study of the thermal decomposition of 2,2'-azobis(2-methylpropionitrile) radical chemistry using a dual-mode EPR resonator. Research on Chemical Intermediates 49 , pp. 289-305. 10.1007/s11164-022-04861-z

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Abstract

A custom-built dual-mode EPR resonator was used to study the radical chemistry of AIBN thermal decomposition. This resonator enables both simultaneous in situ heating using microwaves and EPR measurements to be performed. The thermal decomposition of AIBN was compared following conventional heating methods and microwave-induced (or dielectric) heating methods. Under both heating conditions, the radicals formed and detected by EPR include the 2-cyano-2-propyl (CP●) and 2-cyano-2-propoxyl (CPO●) radicals. Under aerobic conditions, the observed relative distribution of these radicals as observed by EPR is similar following slow heating by conventional or dielectric methods. In both conditions, the kinetically favoured CPO● radicals and their adducts dominate the EPR spectra up to temperatures of approximately 80–90 °C. Under anaerobic conditions, the distribution can be altered as less CPO● is available. However, the observed results are notably different when rapid heating (primarily applied using a MW-induced T-jump) is applied. As the higher reaction temperatures are achieved on a faster timescale, none of the ST●-CPO adducts are actually visible in the EPR spectra. The more rapid and facile heating capabilities created by microwaves may therefore lead to the non-detection of radical intermediates compared to experiments performed using conventional heating methods.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Engineering Chemistry
Publisher:	Springer
ISSN:	0922-6168
Funders:	EPSRC
Date of First Compliant Deposit:	8 February 2023
Date of Acceptance:	22 October 2022
Last Modified:	06 Jan 2024 04:24
URI:	https://orca.cardiff.ac.uk/id/eprint/154553

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