Thiophosphates inhibitors

Metal complexes, dialkyl thiophosphates and dialkyl thiocarbamates of Zn, Ni, Ba, and Ca, in particular, are widely used for the stabilization of lubricants [30-32,34]. At moderate temperatures (350 400 K), these inhibitors are less efficient than phenols, but they are more potent at higher temperatures (430 480 K). The sophisticated mechanism of action of these antioxidants involves their reactions with hydroperoxide. The interaction of hydroperoxide with metal dialkyl thiophosphates induces a cascade of reactions [5,66-69],... 

A combined addition of a chain-breaking inhibitor and a hydroperoxide-breaking substance is widely used to induce a more efficient inhibition of oxidative processes in polyalkenes, rubbers, lubricants, and other materials [3 8]. Kennerly and Patterson [12] were the first to study the combined action of a mixture, phenol (aromatic amine) + zinc dithiophosphate, on the oxidation of mineral oil. Various phenols and aromatic amines can well serve as peroxyl radical scavengers (see Chapter 15), while arylphosphites, thiopropionic ethers, dialkylthio-propionates, zinc and nickel thiophosphates, and other compounds are used to break down hydroperoxide (see Chapter 17). Efficient inhibitory blends are usually prepared empirically, by choosing such blend compositions that induce maximal inhibitory periods [13],... 

There are few potent competitive inhibitors for alkaline phosphatase (Table VII) (4, 21, 94, 96, 100, 105-109). Phosphate, thiophosphate, and arsenate have low values for KThese substances are actually substrates and can form a covalent intermediate. However, this is probably not the reason why they are potent inhibitors since in the case of phosphate the Michaelis complex is more stable than the covalent intermediate (30). The values of Kt for phosphate and arsenate at various pH values have been published (SO, 106, 110). 

Several corrosion inhibitors such as polyamide, polyamine, dithiocarbamate, thiophosphate ester, organic acid, sulfide, and selenide types have all been tried in methanol without significant success [3.5]. Similarly, nonmetallic coatings of metals to effectively prevent corrosion have not been developed to date. One application where coatings have proven effective is in prevention of anodic dissociation of fuel pumps immersed in methanol. Since methanol is many times more conductive than gasoline, components such as fuel pumps and electrical fuel level gauges can cause induced currents that in turn remove metal from these... 

The chain terminating additives are usually aromatic amines, phenols, or sulfides. Those that inhibit the catalytic effect of metallic ions such as Cu, Fe, Pb, Mn, and Co are generally organic sulfides, phosphites, or thiophosphates. Although oxidation or corrosion inhibitors are frequently referred to separately, many of the phosphorus and sulfur containing compounds are effective in both applications. The entire matter of oxidation is affected by many things, including the temperature of the lubricant and the material of construction of the equipment in which the lubricant is used. It is also materially affected by inherent resistance of the base oil to oxidation. 

Techniques. In 1962, McKinley and Read (42) developed an esterase-inhibition technique for the detection of organophosphate pesticide residues on paper chromatograms. The procedure involved conversion of the thiophosphates with bromine to yield active esterase inhibitors, the inhibition by the pesticide of the esterases from a beef liver homogenate sprayed onto the chromatogram, the hydrolysis of the substrate (a-naph-thyl acetate) which was sprayed onto the paper after the liver homogenate had dried, and the development of a background color between Fast Blue RR and the hydrolysis product, a-naphthol. 

Thiophosphate insecticides are protoxins, as they are unable to phosphorylate the serine until after the first liver passage, during which the thiono group is replaced by an 0x0 group. Therefore, they are called indirect acetylcholinesterase inhibitors. 

Thiophosphates and Phosphoramidates.—Adenosine 5 -0-(l-thiodiphosphate) (19a) and adenosine 5 -0-(2-thiodiphosphate) (19b) are not phosphorylated by ATP synthetase in oxidative phosphorylation, but are potent inhibitors of... 

In the selection of an appropriate corrosion inhibitor, an important consideration is the problem of adverse competition with other additives designed to adsorb on the liquid-metal interface. Extreme pressure and/or antiwear agents compete for the same sites as the corrosion inhibitor. Eatty amines are good corrosion inhibitors in this type of environment. However, their adverse effect on the performance of ZDDP additives often prohibits their use. Half esters or amides of dodecylsuccinic acid, phosphate esters or thiophosphates are frequently employed. A combination of inhibitors is sometimes used, for example, fatty carboxylic acids or the dimer/trimer analogues of the unsaturated acids, e.g. oleic, used in conjunction with an amine such as an ethanolamine or alkyl amine, or amide such as alkyl imidazoline and sarcosines, Eig. 6.7. Shorter chain carboxylic acid and amines are used as volatile corrosion inhibitors. 

Various organic compounds are useful as corrosion inhibitors, such as acetylene derivatives, heterocyclic compounds containing nitrogen, sulfur and/or oxygen, long-chain aldehydes and ketones, amines, carboxylic acids and their derivatives, thiourea derivatives and thiophosphates. 

Some compounds retard oxidation entering simultaneously into several reactions. For example, they react with both alkyl and peroxyl radicals (anthracene, methyl-enequinone), decompose hydroperoxides, and terminate chains in the reaction with RO 2 (metal carbamates and thiophosphates). Such compounds are inhibitors of com-... 

If in the chain initiated reaction when v,- = const the induction period is independent of the efficiency of retardation action of the inhibitor but is determined by its concentration, then during autoxidation the inhibitor is more slowly consumed when it more efficiently terminate chains because ROOM is more slowly accumulated and the retardation period increases. Then the initiated oxidation of hydrocarbons is retarded only by compounds terminating chains. Autoxidation is retarded by compounds decomposing hydroperoxides. This decomposition, if it is not accompanied by the formation of free radicals, decreases the concentration of the accumulated hydroperoxide and, hence, the autoxidation rate. Hydroperoxide decomposition is induced by compounds of sulfur, phosphorus and various metal complexes, for example, thiophosphate, thiocarbamates of zinc, nickel, and other metals. 

The combined introduction of an inhibitor, which terminates chains, and a substance, which decomposes hydroperoxides, is widely used for the more efficient retardation of oxidation processes in polyolefins, resins, lubricants, and other materials. Various phenols, bisphenols, and aromatic amines are applied as an acceptor of RO 2, and aryl phosphites, esters of thiopropionic acid, dialkyl dithiopropionates and thiophosphates of zinc and nickel, and other similar compounds are introduced to... 

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