The antioxidant activity of phosphorus compounds—Part I: Decomposition of hydroperoxides by pentaerythritol diphosphites

Soybean Oil-Based Lubricants: A Search for Synergistic Antioxidants

“…Four possible explanations can be considered. The first one for this synergism is the presence of sulfur in metal dithiocarbamates, which has been attributed to the formation of various sulfur oxyacids during hydroperoxide decomposition. , These acids participate in the antioxidant mechanism by an acid-catalyzed ionic decomposition of the hydroperoxides. , The acid species formed might be dialkylhydrogendithiocarbamate R 2 NCS 2 H derived from ZDDC as shown in Scheme a. A similar acid species was reported to be formed from zincdialkyldithiophosphate, , which was a better antioxidant than the parent additive itself .…”

Lubricating Oil Oxidation and Stabilisation

“…Sulphur is the key element in ZDDPs and the acid catalysts will be sulphur-containing since zinc phos phates and phosphoric acids are not effective as antioxidants or peroxide decomposers [142,145,164,166,167]. Infra-red analysis of the products from the reactions of hydroperoxides with pentaerythritol dithiophosphates [169] and nickel dithiophosphates [170,171] also led these authors to propose that PS x O y H species were formed, which together with SO x and H 2 S0 4 , were the active peroxide decomposer species. Infra-red analysis of the products from the reactions of hydroperoxides with pentaerythritol dithiophosphates [169] and nickel dithiophosphates [170,171] also led these authors to propose that PS x O y H species were formed, which together with SO x and H 2 S0 4 , were the active peroxide decomposer species.…”

Role of additives and transition metals in lubricating oil oxidation

“…The key element which accounts for this dual activity of metal dithio complexes is considered to be sulfur, but the metal component will also affect the reactivity of the sulfur atoms and also the overall stability of the complex. Dialkylphosphoric acid derivatives, with no sulfur present, do not inhibit hydrocarbon autoxidation (Kuz'mina et al, 1970) or act as peroxy radical scavengers (Burn, 1966) or peroxide decomposers (Holcik et al, 1983).…”

“…[R02;]- and ZDCs as peroxide decomposers has been attributed to the formation of various sulfur-oxyacids (Holcik et al, 1983;Al-Malaika et al, 1983), and the action of ZDPs has been attributed to the formation of sulfuric acid (Ohkatsu et al, 1978). Product distribution studies from the decomposition of cumene hydroperoxide by ZDPs and ZDCs have confirmed that a strong acid catalyst is responsible (Bridgewater et al, 1980;Sexton, 1985).…”