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The antioxidant activity of polysulfides: it's radical!

Olefin sulfurization, wherein alkenes and sulfur are heated together at high temperatures, produces branched polysulfides. Due to their anti-wear properties, they are indispensible additives to lubricants, but are also added to other petroleum-derived products as oxidation inhibitors. Polysulfides a...

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Autores principales: Chauvin, Jean-Philippe R., Griesser, Markus, Pratt, Derek A.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Royal Society of Chemistry 2019
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6524666/
https://www.ncbi.nlm.nih.gov/pubmed/31183049
http://dx.doi.org/10.1039/c9sc00276f
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author Chauvin, Jean-Philippe R.
Griesser, Markus
Pratt, Derek A.
author_facet Chauvin, Jean-Philippe R.
Griesser, Markus
Pratt, Derek A.
author_sort Chauvin, Jean-Philippe R.
collection PubMed
description Olefin sulfurization, wherein alkenes and sulfur are heated together at high temperatures, produces branched polysulfides. Due to their anti-wear properties, they are indispensible additives to lubricants, but are also added to other petroleum-derived products as oxidation inhibitors. Polysulfides also figure prominently in the chemistry and biology of garlic and other plants of the Allium species. We previously reported that trisulfides, upon oxidation to their corresponding 1-oxides, are surprisingly effective radical-trapping antioxidants (RTAs) at ambient temperatures. Herein, we show that the homolytic substitution mechanism responsible also operates for tetrasulfides, but not trisulfides, disulfides or sulfides. Moreover, we show that this reactivity persists at elevated temperature (160 °C), enabling tetrasulfides to not only eclipse their 1-oxides as RTAs, but also hindered phenols and alkylated diphenylamines – the most common industrial antioxidant additives. The reactivity is unique to higher polysulfides (n ≥ 4), since homolytic substitution upon them at S2 yields stabilized perthiyl radicals. The persistence of perthiyl radicals also underlies the greater reactivity of polysulfides at elevated temperatures relative to their 1-oxides, since homolytic S–S bond cleavage is reversible in the former, but not in the latter. These results suggest that olefin sulfurization processes optimized for tetrasulfide production will afford materials that impart significantly better oxidation stability to hydrocarbon-based products to which polysulfides are added. Moreover, it suggests that RTA activity may contribute to the biological activity of plant-derived polysulfides.
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spelling pubmed-65246662019-06-10 The antioxidant activity of polysulfides: it's radical! Chauvin, Jean-Philippe R. Griesser, Markus Pratt, Derek A. Chem Sci Chemistry Olefin sulfurization, wherein alkenes and sulfur are heated together at high temperatures, produces branched polysulfides. Due to their anti-wear properties, they are indispensible additives to lubricants, but are also added to other petroleum-derived products as oxidation inhibitors. Polysulfides also figure prominently in the chemistry and biology of garlic and other plants of the Allium species. We previously reported that trisulfides, upon oxidation to their corresponding 1-oxides, are surprisingly effective radical-trapping antioxidants (RTAs) at ambient temperatures. Herein, we show that the homolytic substitution mechanism responsible also operates for tetrasulfides, but not trisulfides, disulfides or sulfides. Moreover, we show that this reactivity persists at elevated temperature (160 °C), enabling tetrasulfides to not only eclipse their 1-oxides as RTAs, but also hindered phenols and alkylated diphenylamines – the most common industrial antioxidant additives. The reactivity is unique to higher polysulfides (n ≥ 4), since homolytic substitution upon them at S2 yields stabilized perthiyl radicals. The persistence of perthiyl radicals also underlies the greater reactivity of polysulfides at elevated temperatures relative to their 1-oxides, since homolytic S–S bond cleavage is reversible in the former, but not in the latter. These results suggest that olefin sulfurization processes optimized for tetrasulfide production will afford materials that impart significantly better oxidation stability to hydrocarbon-based products to which polysulfides are added. Moreover, it suggests that RTA activity may contribute to the biological activity of plant-derived polysulfides. Royal Society of Chemistry 2019-04-25 /pmc/articles/PMC6524666/ /pubmed/31183049 http://dx.doi.org/10.1039/c9sc00276f Text en This journal is © The Royal Society of Chemistry 2019 http://creativecommons.org/licenses/by-nc/3.0/ This article is freely available. This article is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported Licence (CC BY-NC 3.0)
spellingShingle Chemistry
Chauvin, Jean-Philippe R.
Griesser, Markus
Pratt, Derek A.
The antioxidant activity of polysulfides: it's radical!
title The antioxidant activity of polysulfides: it's radical!
title_full The antioxidant activity of polysulfides: it's radical!
title_fullStr The antioxidant activity of polysulfides: it's radical!
title_full_unstemmed The antioxidant activity of polysulfides: it's radical!
title_short The antioxidant activity of polysulfides: it's radical!
title_sort antioxidant activity of polysulfides: it's radical!
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6524666/
https://www.ncbi.nlm.nih.gov/pubmed/31183049
http://dx.doi.org/10.1039/c9sc00276f
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