Mechanism of antioxidant action: reactions of alkyl and aryl sulphides with hydroperoxides

Abstract

The aryl sulphides 3,3',5,5'-tetra-t-butyl-4,4'-dihydroxydiphenyl sulphide (1 ), the corresponding disulphide (2). trisulphide (3). and tetrasulphide (4). and the alkyl sulphides di-t-butyl sulphide (7) and dibenzyl disulphide (1 0) have been used to catalyse the decomposition of I -methyl-1 -phenylethyl hydroperoxide (cumene hydroperoxide) a t 393 K. The decompositions are catalytic pseudo-first-order reactions. The kinetic data and product studies demonstrate that the catalyst for hydroperoxide decomposition is sulphur dioxide. The mechanism for formation of the sulphur dioxide has been demonstrated to involve oxidation of the sulphides and decomposition of the resulting thermally unstable sulphur-oxygen compounds. The results demonstrate that the thermal chemistry of sulphur-oxygen compounds (sulphoxides. thiolsulphinates, etc.) formed from the sulphides determines whether or not the sulphide will catalyse hydroperoxide decomposition. RESULTS AND DISCUSSIONAt 393 K the aryl sulphides (1)-( 4), the sulphoxide (5), the thiolsulphonate (6), di-t-butyl sulphide (7), di-

Antioxidants Classification and Applications in Lubricants

“…According to Bridgewater and Sexton [30], sulfur dioxide functions as a powerful Lewis acid such that one equivalent can decompose up to 20,000 equivalents of cumene hydroperoxide, i.e., 5-60 Â 10 À6 mol/l of the sulfur compound decomposed over 50% of the 0.2 mol/l of cumene hydroperoxide in a 6-h period [30].…”

Multifunctional Antioxidants with High Activity at Elevated Temperatures Based on Intramolecular Synergism

“…[5] The formed diarylaminyl radical moiety in 1 can react with peroxyl radicals to generate nitroxides, which can further trap the alkyl radicals to form alkoxyamines. The remarkable activity of SSPDs can be summarized in four points: firstly, the large conjugated system provided by the phenolic Schiff base moiety can greatly stabilize the formed diphenylaminyl radical and facilitate their reaction towards the radicals; secondly, ROOH can be decomposed intramolecularly without escaping from the "cage", so as to reduce the possibility of degrading into more radicals before being captured by the added peroxide decomposers; [20] thirdly, all of the generated sulfur-bearing derivatives have the distinctive capacity to decompose more peroxides; [21] finally, the diphenylamine can be quickly regenerated, resulting in the large stoichiometric efficiency per molecule. [19] The sulfoxide moiety can be further oxidized to form sulfone, sulfinic acid or sulfuric acid.…”

Thermal stability of aviation kerosines: techniques to characterize their oxidation properties

“…Bridgewater and Sexton (1978) propose that SOz, formed by the oxidation of sulfides, is the active species in the acid catalysis. Bridgewater and Sexton (1978) propose that SOz, formed by the oxidation of sulfides, is the active species in the acid catalysis.…”

“…The key processes involved in radical oxidation mechanisms such as chain propagation, radical scission, and radical-radical self-termination are well understood, and the determination of their rates has been reviewed by Mill and Hendry (1980). To a lesser extent, the mechanism of inhibition by sulfur compounds has also been investigated (Bridgewater and Sexton, 1978) as have been their oxidation products (Koelewijn andBerger, 1972, 1974).…”