Organosulfur Antioxidants in Hydrocarbon Oils

The antioxidant activity of polysulfides: it's radical!

“…The antioxidant mechanisms of organosulfur compounds are generally believed to be ionic ‘secondary antioxidant’ processes, where they react with (hydro)peroxides directly or via the eventual formation of sulfur dioxide or sulfur oxyacids 3. Moreover, it is generally accepted that all polysulfides are equally competent at inhibiting the oxidation of hydrocarbons when normalized to the number of sulfur atoms in the chain ( i.e.…”

“…However, great efforts were made to remove the organosulfur compounds during the refining process due to their propensity to form corrosion-inducing acids. Over time, synthetic organosulfur compounds were introduced into lubricants (and some other petroleum-derived products) because of their excellent anti-wear properties, particularly at extreme pressures,3–5 and those compounds with the best balance of maximum anti-wear properties and minimum corrosive effects were identified, developed, and incorporated into commercial products.…”

Polysulfide-1-oxides react with peroxyl radicals as quickly as hindered phenolic antioxidants and do so by a surprising concerted homolytic substitution

“…However, it is generally acknowledged that they must first be oxidized to render them effective. 4 Organosulfur compounds are ascribed ‘secondary antioxidant’ activity since it is believed that they slow the rate of initiation (eqn (1)) by decomposing hydroperoxides. 5 Two mechanisms are particularly important in this context: the direct reduction of hydroperoxides (eqn (5)) and the production of Brønsted or Lewis acids, which catalytically decompose hydroperoxides (eqn (6)) ( Scheme 2 ).…”

“…Since trisulfides and their oxides are among the most prevalent organosulfur compounds in Allium species ( e.g. , diallyltrisulfide and diallyltrisulfide-1-oxide from garlic) 18 , 19 and are predominant among the mixtures of sulfurized materials added to protect petroleum-derived products from autoxidation, 4 , 20 we wondered if they would possess ‘primary antioxidant’ reactivity analogous to that of hindered sulfoxides and activated thiosulfinates. Herein we report an investigation of the RTA activities of some trisulfides and their 1-oxides in an attempt to extend the foregoing knowledge to a more comprehensive view of the primary antioxidant activity of polysulfides and their 1-oxides, in general.…”

Estudo do comportamento de biofluidos de óleos de palma e soja com antioxidantes na têmpera de aços, antes e após o envelhecimento acelerado

“…Os antioxidantes têm como funcionalidade neutralizar quimicamente a ação dos radicais livres, que atuam no início do processo de oxidação impedindo ou minimizando a formação de compostos como peróxidos, Assim formam-se espécies inativas para a reação em cadeia e um radical inerte (A•) proveniente do antioxidante. Este radical, estabilizado por ressonância, não tem a capacidade de iniciar ou propagar as reações oxidativas (KORCEK;JENSEN, 1975;HARPP et al, 1985;IGARASHI, 1990;RAMALHO;JORGE, 2006).…”