Studies Involving Alkane Activation

During a study of the reactions of aromatic hydrocarbons with the hydrides formed by reducing cobalt(III) acetylacetonate with triisobuty-laluminum, Tyrlik and Michalski (98) observed that some of the cumene solvent is converted to ethylbenzene, e.g., 

It is suggested that this occurs by interaction of the isopropyl side chain with the cobalt complexes in solution, leading to C—C bond cleavage and subsequent hydrogenation (97). 

Evidence of an interaction between a transition metal and methane has come from a rather unusual source (37). When Cr(CO)6 is photo-lyzed in a solid methane glass at 20 K, the expected CifCO) is not, as had been thought, of Dih symmetry (XLI), but instead is Cr(CO)5-methane in which the Cr(CO)5 is of C4V symmetry (XLII)  

A solution of palladium(II) sulfate in sulfuric acid absorbs alkanes and reacts with them (Si). The reaction taking place is unclear, but it is suggested that hydrogen abstraction from the alkane occurs as the first step and this is then followed by sulfonation or oxidation. Products of the reaction have not been given. 

Finally, it may be noted that the manganese and chromium oxyanions (permanganate and chromate) are known to oxidize alkanes readily (102). In these reactions there is not any direct interaction between the transition metal and the alkane the favored mechanism for chromate oxidation is 

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In fact, the selective catalytic removal of NO in presence of excess oxygen remains a challenge. Most of the cunent studies involve C1-C4 hydrocarbons as reductants and zeolites as catalysts, among which Cu-exchanged MFI zeolites are considered as one of the most active [2]. The reductant shows a complex influence in this reaction it has been thus reported that a Cu/Zr02 catalysts are active with pro-pene but show low activity with propane as reductant [3]. For a practical use reduction by higher alkanes would be attractive, siiKe it would be easier to handle in a vehicle. 

Alkanes can be activated by both hard and soft transition metal complexes. Hard catalysts have been known for a long time, although examples involving alkanes are few in number, and all are from studies of recent years. Soft catalysts have become important and have been much studied during the past decade and are widely used for reactions of unsaturated hydrocarbons. It was the use of such soft catalysts that Halpem had particularly in mind when he spoke of the development to activate alkanes as an important and challenging problem. 

A variety of halogenated alkanes and alkenes such as hexachlorobutadiene, chlorotrifluoro-ethylene, tetrafluoroethylene, and trichloroethylene (Fig. 7.28) are nephrotoxic. Studies have shown that metabolic activation is necessary for toxicity, but this does not involve cytochromes P-450. Thus, hexachlorobutadiene (HCBD) is a potent nephrotoxin in a variety of mammalian species, and the kidney is the major target. 

According to an early report, sulfated zirconia promoted with 1.5% Fe and 0.5% Mn increased the rate of isomerization of n-butane to isobutane by several orders of magnitude at modest temperature (28°C).299 This reactivity is surprising, since the isomerization of n-butane in strong liquid acids takes place at a rate much lower than that of higher alkanes, which is due to the involvement of the primary carbocationic intermediate. In addition, other solid acids, such as zeolites, did not show activity under such mild conditions. Evidence by isotope labeling studies with double-labeled n-butane unequivocally shows, however, that the isomerization of... 

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