Modelling the mechanism and kinetics of the radical scavenging activity of iminostilbene. (March 2021)

• Record Type: Journal Article
• Authors: Vo, Quan V.; Van, Le Thi Ngoc; Hoa, Nguyen Thi; Mechler, Adam
• Is Part Of: Polymer degradation and stability. Volume 185(2021)
• Publication Date: 2021-03
• Subjects: Polymerization inhibitor -- Radical polymerization -- Antioxidants -- Mechanism -- Kinetic -- Antiradical activity; Polymers -- Deterioration -- Periodicals; Stabilizing agents -- Periodicals; Polymères -- Dégradation -- Périodiques; Stabilisants -- Périodiques; 668.9
• DOI: 10.1016/j.polymdegradstab.2021.109483
• Languages: English
• ISSNs: 0141-3910

Abstract

Highlights: Iminostilbene (IS) exhibits excellent HO and TBO scavenging activity. The radical scavenging activity against HOO is moderate ( k overall = ~ 10 4 M −1 s −1 ). The rate constant of the HO antiradical activity in benzene is 7.20 × 10 9 M −1 s −1 . For TBO scavenging activity in benzene, the rate constant is 2.10 × 10 8 M −1 s −1 . Comparison with experimental data in benzene yields k calculated /k experimetal = 0.3. Consistently IS is a promising artificial scavenger. Abstract: Iminostilbene (IS ) (5H‐dibenz[b, f]azepine) is frequently used as a polymerization inhibitor to stop the reactions of radical polymerization. The compound itself is considered an antioxidant; however, little is known about the mechanism and kinetics of its activity. In this study, the antiradical activity of IS against typical radicals i.e. HO, HOO and TBO ( tert -butoxy radical) has been evaluated by computational methods. It was found that IS exhibits excellent HO and TBO scavenging activity in gas phase and in lipid-mimetic environment (benzene), whereas its activity against HOO is moderate with k overall = ~ 10 4 M −1 s −1 . The overall rate constants of the HO antiradical activity are k overall = 7.06 × 10 11 and 7.20 × 10 9 M −1 s −1 in gas phase and benzene, respectively, whereas for the TBO antiradical activity in benzene it is 2.10 × 10 8 M −1 s −1 . Comparison with the experimentally determined rate constant in benzene ( k (BTO ) = 7.8 × 10 8 M −1 s −1 ) yields the k calculated / k experimetal ratio of 0.3; thus, the computed kinetic data are reasonably accurate. It was shown that the TBO and HOO radicals scavenging of IS mostly follows the FHT mechanism at the NH bond; however, in case of the HO radical both FHT (at NH bond) and RAF (at C10 position) mechanisms contribute to the observable activity. Graphical abstract: Image, graphical abstract