31562-41-1Relevant articles and documents
The antioxidant activity of polysulfides: It's radical!
Chauvin, Jean-Philippe R.,Griesser, Markus,Pratt, Derek A.
, p. 4999 - 5010 (2019/05/29)
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.
A kinetic study of S-nitrosothiol decomposition
Grossi, Loris,Montevecchi, Pier Carlo
, p. 380 - 387 (2007/10/03)
Under anaerobic conditions S-nitrosothiols 1a-e undergo thermal decomposition by homolytic cleavage of the S-N bond; the reaction leads to nitric oxide and sulfanyl radicals formed in a reversible manner. The rate constants, k1, have been determined at different temperatures from kinetic measurements performed in refluxing alkane solvents. The tertiary nitrosothiols 1c (k1(69°C) = 13 × 10-3 min-1) and 1d (k1(69°C) 91 × 10-3 min-1) decomposed faster than the primary nitrosothiols 1a (k1(69°C) = 3.0 × 10-3 min-1) and 1b (k1(69°C) = 6.5 × 10-3 min-1). The activation energies (E#= 20.5 - 22.8 Kcal mol-1) have been calculated from the Arrhenius equation. Under aerobic conditions the decay of S-nitrosothiols 1a-e takes place by an autocatalytic chain-decomposition process catalyzed by N2O3. The latter is formed by reaction of dioxygen with endogenous and/or exogenous nitric oxide. The autocatalytic decomposition is strongly inhibited by removing the endogenous nitric oxide or by the presence of antioxidants, such as pcresol, β-styrene, and BHT The rate of the chain reaction is independent of the RSNO concentration and decreases with increasing bulkiness of the alkyl group; this shows that steric effects are crucial in the propagation step.
Oxidation of Bis(tert-butylthio) Selenide at Low Temperatures: Search for a Bis(alkylthio) Selenoxide
Kice, John L.,Wilson, Dean M.,Espinola, John M.
, p. 3520 - 3524 (2007/10/02)
Oxidation of bis(tert-butylthio) selenide, t-BuSSeSBu-t (1a), by peracetic acid at -40 deg C leads to a monooxidation product (1a-O) whose 1H (two singlets) and 13C NMR spectra (four resonances) show that the two tert-butyl groups in 1a-O are magnetically nonequivalent.It cannot therefore be the bis(alkylthio) selenoxide, t-BuSSe(O)SBu-t (3a), and is either t-BuS(O)SeSBu-t, 5a (oxidation of 1a at S rather than Se), or t-BuSSeOSBu-t, 4a (formed by rapid isomerization of initially formed 3a).The fact that δ 77Se for 1a-O is 289 ppm downfield from δ 77Se for 1a is inconsistent with structure 5a and indicates that 1a-O has structure 4a, t-BuSSeOSBu-t.Reaction of t-BuSH with 1a-O gives 1a plus t-BuSOH, in accord with what would be expected for nucleophilic attack of the thiol on the selenium of 4a.While oxidation of 1a by peracid is thought to result initially in 3a, this thioselenoxide apparently isomerizes to 4a so rapidly, even at -40 deg C, that 4a is the first oxidation product detectable by NMR.These results are of significance with regard to several steps in the previously proposed (ref 4) mechanism (Scheme 1) for the formation of bis(alkylthio) selenides from the reaction of thiols with selenite.
