Direct dehydrogenation

All attempts to effect direct dehydrogenation of tetrahydro- and octahydroindeno[1,2-t/]aze-pines with palladium on charcoal or with trityl perchlorate have failed.57... 

For a lead reference and a particularly elegant example of the (site-directed) dehydrogenation of an aliphatic group incorporated into a complex organic synthesis see D. Sames in ... 

With inflexible substrates, this photochemical functionalization process showed significant selectivity. As our first example, photolysis of steroid ester 70 led to carbonyl insertion into the C-H bonds at C-7 and C-14 [149,150]. Other steroid esters afforded selective functionalizations in various positions [e.g. 151, 152], and compound 71 directly dehydrogenated the steroid to form the product olefin 72 [150]. 

Direct dehydrogenation of oximes is also possible, particularly for sterically hindered nitrile oxides. The most successful oxidizing agents are alkaline hypobromite and NBS in the presence of base, the latter being valuable when basic groups are present. Lead tetraacetate and alkaline hypochlorite have also been employed, but the yields are lower. The formation of furoxans from the reaction of alkoximes with nitrogen oxides is believed to proceed via the corresponding nitrolic acids. 

Other Isobutane-Based Chemicals. Isobutane can be directly dehydrogenated to isobutylene by a modification of the Houdry process. This can then be converted to MTBE. The estimated use is over 1 billion lb of isobutane. Because of their inertness and higher vapor pressures, high-purity propane and butanes have become the important substitutes for fluorocarbons as aerosol propellants. Isobutane can also be used as a solvent in polymer processing, and as a blowing agent for foamed polystyrene. 

Ring-c aromatic steroids hydroxylated at C-7 have also been described.49 Direct dehydrogenation of 3/3 -hydroxy-17,17-dimethyl-18-nor-5 a -androst-13-ene with... 

If this process is compared with direct dehydrogenation, the addition of 10 to 20 per cent volume of oxygen to the feedstocks serves to boost the production capacity by at least 25 per cent, by raising the once-through yield. The use of oxygen has the following effects ... 

Styrene is manufactured nearly entirely by the direct dehydrogenation of ethylbenzene. Smaller amounts are obtained indirectly, as a co product, from the production of propy. lene oxide by the Oxirane and Shell technologies, industrialized in the United States, the Netherlands and Spain, and whose essential intermediate step is the formation of ethylbenzene hydroperoxide, or from the production of aniline, by a technique develop jn the USSR, which combines the highly exothermic hydrogenation of nitrobenzene with the highly endothermic dehydrogenation of ethylbenzene. 

Supported vanadium catalysts, whereby vanadium oxide is dispersed on a support such as alumina or titania are of particular importance in, for instance, the oxidative dehydrogenation of alkanes [58-64]. Such materials have attracted considerable interest in the direct dehydrogenation of butane, where a key driver is to identify the relationship between catalytic activity and structural properties [5, 6, 65-68]. In the pure (solid) metal oxides the coordination of vanadium is well defined. However, this is not necessarily true in the case of supported catalysts. Vanadium may be present on the support surface as isolated vanadium ions dimeric or polymeric species one- and two-dimensional chains of vanadium ions ... 

Thus, the product of direct dehydrogenation of higher normal paraffins is one diluted with a considerable amount of unreacted paraffin. The monoolefin and paraffin usually have rather close boiling points and cannot be separated readily by distillation. Separation must be effected by subjecting the olefin to some desired secondary reaction, or by some other means, and the unreacted paraffin is then ultimately recycled to the dehydrogenation process. 

As to the problem of whether or not Cu, which is inside the frame of Table III, is a catalyst for dehydrogenation of cyclohexane and for hydrogenation of benzene, a discussion has been carried on. A recent study of Erofeev and Nikiforova (203), with the application of UV spectroscopy showud that copper is indeed a catalyst in this reaction, as well as in the direct dehydrogenation of cyclohexane to benzene. This... 

Here Wi is the rate of doublet dehydrogenation of cyclohexane into cyclohexene W[, that of the reverse reaction Ws, the rate of dehydrogenation of cyclohexene into benzene and W2, the rate of the direct dehydrogenation of cyclohexane into benzene. 

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