Zinc, dialkyls

However, the most widely used materials are the zinc dialkyl-dithiophosphates that have an anti-wear effect in addition to their antioxidant power and, besides, offer an attractive cost/effectiveness ratio. 

Zinc dialkyl dithiophosphates are the primary oxidation inhibitors in combining these functions with antiwear properties in automotive oils and high pressure hydrauhc fluids. Their production volume is followed by aromatic amines, sulfurized olefins, and phenols (22). 

In steel-on-steel lubrication with a zinc dialkyl dithiophosphate additive, a complex surface paste appears to form first of zinc particles and iron dithiophosphate. The iron dithiophosphate then thermally degrades to a brown surface film of ZnS, ZnO, FeO, plus some iron and zinc... 

CO2 insertion into M C bonds has, of course, been known since the first papers of V. Grignard in 1901 (p. 134). Organo-Li (and other M and M") also react extremely vigorously to give salts of carboxylic acids, RCO Li, (RC02)2Be, etc. Zinc dialkyls are much less reaetive towards CO2, e.g. 

The salts of alkyl xanthates, A/,A/ -di-substituted dithio-carbamates and dialkyidithiophosphates [26] are effective peroxide decomposers. Since no active hydrogen is present in these compounds, an electron-transfer mechanism was suggested. The peroxide radical is capable of abstracting an electron from the electron-rich sulfur atom and is converted into a peroxy anion as illustrated below for zinc dialkyl dithiocarbamate [27] ... 

Zinc, chlorohexadecakis(pheny thio)octakis-, 1,137 Zinc, dialkyl-oxidation, 2, 342 Zinc, dicyano-... 

Tetraethyltin ZDDP, ZDTP Zinc dialkyl dithiophosphates... 

The monocation tris(diethylether) ethylzinc is formed from diethyl zinc as a tetrakis(penta-fluorophenyl)borate salt.85 Longer-chain linear and cyclic ether complexes (2) of zinc alkyls have also been observed. The reaction between zinc dialkyls and primary amines gives a number of structurally diverse products dependent on the reaction conditions and the amine.86 The... 

The resulting products, such as sulfenic acid or sulfur dioxide, are reactive and induce an acid-catalyzed breakdown of hydroperoxides. The important role of intermediate molecular sulfur has been reported [68-72]. Zinc (or other metal) forms a precipitate composed of ZnO and ZnS04. The decomposition of ROOH by dialkyl thiophosphates is an autocata-lytic process. The interaction of ROOH with zinc dialkyl thiophosphate gives rise to free radicals, due to which this reaction accelerates oxidation of hydrocarbons, excites CL during oxidation of ethylbenzene, and intensifies the consumption of acceptors, e.g., stable nitroxyl radicals [68], The induction period is often absent because of the rapid formation of intermediates, and the kinetics of decomposition is described by a simple bimolecular kinetic equation... 

Phosphorus is a common component of additives and appears most commonly as a zinc dialkyl dithiophosphate or triaryl phosphate ester, but other forms also occur. Two wet chemical methods are available, one of which (ASTM D1091) describes an oxidation procedure that converts phosphorus to aqueous orthophosphate anion. This is then determined by mass as magnesium pyrophosphate or photochemically as molybdivanadophosphoric acid. In an alternative test (ASTM D4047), samples are oxidized to phosphate with zinc oxide, dissolved in acid, precipitated as quinoline phosphomolybdate, treated with excess standard alkali, and back-titrated with standard acid. Both of these methods are used primarily for referee samples. Phosphorus is most commonly determined using x-ray fluorescence (ASTM D4927) or ICP (ASTM D4951). 

Zinc dialkyl/diaryl dithiophosphates are widely used as antiwear additives in engine oils to protect heavily loaded engine parts from excessive wear. They are also used as antiwear agents in hydraulic fluids. The salts are effective oxidation and corrosion inhibitors, they also act as detergents. During friction, these salts form anion-radicals that are successfully cleaved (Kajdas et al. 1986). 

Mechanism of Oxidation Inhibition by Zinc Dialkyl Dithiophosphates... 

The kinetics of the zinc diisopropyl dithiophosphate-in-hibited oxidation of cumene at 60°C. and Tetralin at 70°C. have been investigated. The results cannot be accounted for solely in terms of chain-breaking inhibition by a simple electrow-transfer mechanism. No complete explanation of the Tetralin kinetics has been found, but the cumene kinetics can be explained in terms of additional reactions involving radical-initiated oxidation of the zinc salt and a chain-transfer step. Proposed mechanisms by which zinc dialkyl dithiophosphates act as peroxide-decomposing antioxidants are discussed. 

Although zinc dialkyl dithiophosphates, [(RO)2PS2]2Zn, have been used as antioxidants for many years, the detailed mechanism of their action is still not known. However, it is certain that they are efficient peroxide decomposers. The effect of a number of organic sulfur compounds, including a zinc dithiophosphate, on the rate of decomposition of cumene hydroperoxide in white mineral oil at 150°C. was investigated by Kennerly and Patterson (13). Each compound accelerated the hydroperoxide decomposition, the zinc salt being far superior in its activity to the others. Further, in each case the principal decomposition product... 

The inhibition of hydrocarbon autoxidation by zinc dialkyl dithiophosphates was first studied by Kennerly and Patterson (13) and later by Larson (14). In both cases the induction period preceding oxidation of a mineral oil at 155 °C. increased appreciably by adding a zinc dialkyl dithiophosphate. In particular, Larson (14) observed that zinc salts containing secondary alkyl groups were more efficient antioxidants than those containing primary groups. In these papers the inhibition mechanism was discussed only in terms of peroxide decomposition. 

More recently it has been shown (6, 7) that zinc dialkyl dithiophosphates also act as chain-breaking inhibitors. Colclough and Cunneen (7) reported that zinc isopropyl xanthate, zinc dibutyl dithiocarbamate, and zinc diisopropyl dithiophosphate all substantially lowered the rate of azobisisobutyronitrile-initiated oxidation of squalene at 60°C. Under these conditions, hydroperoxide chain initiation is negligible, and it was therefore concluded that inhibition resulted from removal of chain-propagating peroxy radicals. Also, consideration of the structure of these zinc dithioates led to the conclusion that no suitably activated hydrogen atom was available, and it was suggested that inhibition could be accounted for by an electron-transfer process as follows ... 

The conclusion that chain-breaking inhibition by zinc dialkyl dithiophosphates involves electron transfer was reached independently by Burn (6) following a more detailed qualitative study of the inhibition of the azonitrile-initiated oxidation of squalane and cumene and the noninitiated oxidation of indene by metal dialkyl dithiophosphates and related compounds (I to IV) ... 

RH) by a zinc dialkyl dithiophosphate (ZnP) should ideally be representable by the following simplified scheme (Reactions 1 to 6). 

One possible problem peculiar to a quantitative study of the inhibition of oxidation of aromatic hydrocarbons by zinc dialkyl dithiophos-phates is that peroxide decomposition could yield a phenol during the initial-rate measurement. Rate curves for the zinc diisopropyl dithio-phosphate-inhibited oxidation of cumene are shown in Figure 7. In the initial presence of hydroperoxide the uninhibited rate is never reached, and the reaction soon exhibits autoinhibition, presumably caused by the... 

Because of the lack of information in the literature on the radical reactions of compounds of quinquevalent phosphorus, it is impossible to postulate a readily acceptable mechanism for the oxidation of zinc dialkyl dithiophosphates. Colclough and Cunneen (7) rejected immediately the possibility of hydrogen abstraction, but in view of the present results serious consideration has been given to this reaction. During this work it was shown (15) that abstraction of hydrogen from trialkyl phosphates, trialkyl phosphonates, and sodium dialkyl phosphates can occur at room temperature in an aqueous medium in the presence of hydroxy radicals. 

Peroxide Decomposition Mechanism. Since virtually no work has been reported which concerns only the mechanism by which zinc dialkyl di-thiophosphates act as peroxide decomposers, it is pertinent to discuss metal dialkyl dithiophosphates as a whole. The mechanism has been studied both by investigating the products and the decomposition rates of hydroperoxides in the presence of metal dithiophosphates and by measuring the efficiency of these compounds as antioxidants in hydrocarbon autoxidation systems in which hydroperoxide initiation is significant. 

Kennerly and Patterson (13) studied the effect of several organic sulfur compounds, including thiols, sulfides, a disulfide, sulfonic acids, and a zinc dialkyl dithiophosphate, on the decomposition rate of cumene hydroperoxide in white mineral oil at 150 °C. In each case they found phenol as the major product. They suggested that the most attractive mechanism by which to explain these results involves ionic rearrangement catalyzed by acids or other electrophilic reagents (10) as... 

Arylzinc halides, and zinc dialkyls and di-aryls may be prepay by the action of the Grignard reagent on anhydrous zinc chloride in ether solution.6... 

Many carbon compounds, e.g. hydrocarbons, ketones, organic acids, bases and esters, dissolve in arsenic trichloride with formation of additive or complex compounds. The organic derivatives of arsenic are described in Volume XI, Part II, of this Series. Trialkyl arsines are formed by the addition of alkali to the double salts obtained by the interaction of zinc dialkyls and arsenic trichloride—... 

In fact it can be assumed that, in the catalytic system TiCl4-bis[(S)-2-methyl-butyl]-zinc, dialkyl zinc alkylates the titanium atom (19) and that the titanium alkyl thus formed gives more stable complexes with the (S) olefin than with the (R) olefin, thus favouring the adsorption and polymerization of the (S) antipode (104). The influence exerted by the asymmetric groups bound to transition metals on the type of complexes formed by olefins with the same metal atom, has been recently investigated by Pajaro, Corradini, Palumbo and Panunzi (90). 

Agrostis tenuis, 963 Zinc, alkylalkoxy-synthesis, 340 Zinc, alkylphenoxy-synthesis, 340 Zinc, dialkyl-oxidation, 342 Zinc complexes acetylacetone, 372 amidines... 

The carbonyl functionality of MIBK can be hydrogenated over nickel catalysts to yield methyl isobutyl carbinol (4-methyl-2-pentanol or methyl amyl alcohol) [108-11-2]. Industrial processes coproduce methyl isobutyl carbinol during the hydrogenation of mesityl oxide to MIBK. The product ratio of methyl isobutyl carbinol—MIBK during this reaction can be shifted toward methyl isobutyl carbinol by adopting a higher than normal pressure and H2 organic ratio (59). Methyl isobutyl carbinol is used as an ore flotation frother and to produce zinc dialkyl dithiophosphate lube oil additives. It is produced in the United States by Shell and Union Carbide ( 1.12/kg, October 1994). 

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