Aluminum conversion importance

Overall, this work highlights how quantum chemical methods can be used to study tribochemical reactions within chemically complex lubricant systems. The results shed light on processes that are responsible for the conversion of loosely connected ZP molecules derived from anti-wear additives into stiff, highly connected anti-wear films, which is consistent with experiments. Additionally, the results explain why these films inhibit wear of hard surfaces, such as iron, yet do not protect soft surface such as aluminum. The simulations also explained a large number of other experimental observations pertaining to ZDDP anti-wear films and additives.103 Perhaps most importantly, the simulations demonstrate the importance of cross-linking within the films, which may aid in the development of new anti-wear additives. 

These results suggest that if we want to design a molecular sieve to separate a mixture of normal hexane and 2-methylpentane, we should use a zeolite with normal sinusoidal pores but small-diameter straight pores such a zeolite will preferentially accept normal -hexane and preferentially reject 2-methylpentane. More important, perhaps, these results have implications for selective catalysis. If we want -hexane to react but not 2-methylpentane, then we should make a zeolite where the catalytically active centers (aluminum oxides) are situated in the sinusoidal pores but not in the straight pores. Conversely, if we desire preferential catalysis for the branched isomer, we want a zeolite where the active centers are at the intersections between straight and sinusoidal pores. 

Flere MAO first generates the dimethyl complex 6.26 from 6.25. This reaction, of course, can also be brought about by Me3Al. It is the subsequent reaction (i.e., the conversion of 6.26 to 6.27 that is of crucial importance. The high Lewis acidity of the aluminum centers in MAO enables it to abstract a CH3 group from 6.26 and sequesters it in the anion, [CH3-MAO]. Although 6.27 is shown as ionically dissociated species, probably the anion, [CH3-MAO], weakly coordinates to the zirconium atom. It is this coordinatively unsaturated species, 6.27, that promotes the alkene coordination and insertion that are necessary for polymerization activity. 

Scheme 9 outlines the synthesis of a prostanoid intermediate (99) that relies on an intermolecular Nozaki process. It is important to note that unlike the intramolecular case described above, the intermolecular version of this protocol requires an aldehyde as the electrophilic trap however, it is interesting to note that there have been no reports of the addition of Lewis acid activated ketones (presumably, as a preformed complex which would be added via cannula at low temperature) to the preformed aluminum enolate. Finally, in this example, the conversion of enone (96) to adduct (98) is promoted by the less reactive dimethylaluminum phenyl thiolate and not the corresponding ate complex. 

Decationation of the process of conversion of the Bronsted to Lewis acid sites that takes place in the temperature range of 400-500° as a result of the evolution of water can be visualized as shown in Fig. 8. The Bronsted acid sites are shown by (A), the Bronsted base by (B), and the Lewis acid site by (C). The specific molecular locale of the Lewis acid site is the three-coordinated aluminum. It can act as an acceptor of H or of one electron. As an acceptor of the H ion it may play an important role in initiating the carbonium type of reactions of the hydrocarbons by facilitating carbonium ion formation. On the other hand, it is also an electron acceptor. Turkevich and Stamires have shown this when they studied the ESR of triphenylamine (an electron donor) on a variety of zeolites. They found that the amount of electron transfer increased... 

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