Sulfur-containing antioxidants

More recendy, molecular molybdenum-sulfur complexes and clusters have been used as soluble precursors for M0S2 in the formulation of lubricating oils for a variety of appHcations (70). Presumably, the oil-soluble molybdenum—sulfur-containing precursors decompose under shear, pressure, or temperature stress at the wear surface to give beneficial coatings. In several cases it has been shown that the soluble precursors are trifunctional in that they not only display antifriction properties, but have antiwear and antioxidant characteristics as weU. In most cases, the ligands for the Mo are of the 1,1-dithiolate type, including dithiocarbamates, dithiophosphates, and xanthates (55,71). 

Potentiometric titration procedures with sodium methoxide have been reported for non-sulfur-containing organotin compounds in solvent extracts of polymers, and for phenolic antioxidants with sodium isopropox-ide in pyridine medium [21]. Organotin compounds in solvent extracts of PVC can be determined by potentiometric and manual titration procedures [487,488]. 

SULFUR-CONTAINING ANTIOXIDANTS 17.3.1 Reaction with Hydroperoxide... 

Sulfur-containing antioxidants reduce hydroperoxide to alcohols, thereby decreasing... 

Methionine (Met or M) ((5)-2-amino-4-(methylsulfanyl)-butanoic acid) is a nonpolar, neutral, amino acid with the formula HOOCCH(NH2)CH2CH2SCH3. Together with Cys, Met is one of the two sulfur-containing proteinogenic amino acids and a great antioxidant. Its derivative 5-adenosyl methionine (SAM) serves as a methyl donor. ... 

Some derivatives of 1,2,3-trithiolane have been used as starting materials for sulfur-containing polymers <84MI 4l5-0l>. Industrial applications for 1,2,3-trithiolane derivatives include their use as high-pressure lubricant oil additives <88EGP258606>, plasticizers and antioxidants <89EGP263770>. 

The mechanisms of inhibition by peroxide decomposers, metal deactivators, and ultraviolet absorbers are fairly well understood in general terms, although many details of the individual reactions remain to be elucidated. Classifying a preventive antioxidant into one of the three categories above will only rarely describe its entire function. The dual behavior of dialkyl dithiophosphates in the liquid phase has been mentioned. Many other phosphorus- and sulfur-containing antioxidants commonly classified as peroxide decomposers can also act as chain breakers. Similarly, the structure of many metal deactivators and ultraviolet absorbers indicates that they must also have some chain-breaking activity. 

Some organosulfur compounds can function as fuel antioxidants by acting to decompose hydroperoxides. Organosulfides are believed to react with hydroperoxides to form sulfoxides. The sulfoxides then further react with hydroperoxides to form other more acidic compounds. These newly formed acids continue the process of decomposing and reaction with hydroperoxides. Thus, organosulfur compounds function in the process oxidation inhibition through hydroperoxide decomposition. However, in most fuel applications, sulfur-containing antioxidants are not utilized. 

Reaction with Peroxyl Radicals Sulfur-Containing Antioxidants... 

Garlic has been reported to have lipid- and blood-pressure-lowering properties, as well as antiplatelet, antioxidant, and fibrinolytic effects. In animal models and human cell cultures, it has been shown to have antiatherosclerotic activity (see Chapter 50). The sulfur-containing component, allicin, is considered to be the principal active ingredient of garlic, but several other bioactive ingredients have also been isolated. 

Influence of the obtained sulfur-containing substances and the shielded phenols on detergent-dispersive action of cuccinimide has been investigated. It has been established, that combination of antiwear and antioxidant additives in an oil composition with cuccinimide allows to appreciably reduce the contents of the latter to maintain sufficiently high operational characteristics of lubricants. 

Selenium is an essential trace element and an integral component of heme oxidase. It appears to augment the antioxidant action of vitamin E to protect membrane lipids from oxidation. The exact mechanism of this interaction is not known however, selenium compounds are found in the selenium analogs of the sulfur-containing amino acids, such as cysteine and methionine. Se-cysteine is found in the active sites of the enzyme glutathione peroxidase, which acts to use glutathione to reduce organic hydroperoxides. 

Non-discoloring, sulfur containing phenolic antioxidant and stabilizer that provides long-term heat stability by preventing thermo-oxidative degradation. Used for the process stabilization of polyethylene wire and cable resins for polyethylene during extruder compounding. Can also be applied in styrenic polymers, polypropylene, elastomers such as EPDM and SBR and for carboxylated SBR latex, polybutadiene rubber and polyisopropene rubber. 

Sulfur containing, high performance primary (phenolic) antioxidant and heat stabilizer used for the base stabilization of polyethylene wire and cable resins. 

In contrast to sulfur-containing tin compounds, tin carboxylates have to be used with antioxidants. The advantage of the use of sulfur-free stabilizers is the good photostability and the lack of odor. These stabilizers, too, need additional lubricants, since they tend to stick to the metal parts of calendars and extruders. ... 

Preventive antioxidants (sometimes referred to as secondary antioxidants) act by interrupting the secondary oxidation cycle to prevent or inhibit the generation of free radicals. The most important preventive mechanism is the nonradical hydroperoxide decomposition, PD. Phosphite esters and sulfur-containing compounds, e.g., AOs 15-24, Table 1, are the most important groups of peroxide decomposers. Phosphite esters are known as stoichiometric peroxide decomposers (PD-S) they reduce hydroperoxides to... 

A wide variety of interactions of selenium with essential and nonessential elements, vitamins, xenobiotics, and sulfur-containing amino acids have been demonstrated in numerous studies. Selenium has been reported to reduce the toxicity of many metals including mercury, cadmium, lead, silver, and to some extent, copper (Frost 1972). Most forms of selenium and arsenic interact to reduce the toxicity of both elements (Levander 1977). Because of selenium s role in the antioxidant glutathione peroxidase enzymes, selenium also reduces the toxicity of metals in vitamin E-deficient animals (Diplock et al. 1967). 

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