Saturated skeletal rearrangements

Triflic acid is strong enough to protonate polycyclic saturated hydrocarbons [77, 78, 79], and even -butane [80, 81], and to initiate skeletal rearrangements Acidic treatment of homoadamantane [77] (equation 32), 2-homoprotoadamantane [78] (equation 33), or as 2,3-trimethylenebicyclo[3 3 Ojoctane [79] (equation 34) causes their rearrangement to isomenc hydrocarbons... 

Under the same conditions, several types of hydrocarbon are also converted to fully deuterated compounds. The results are summarized in Table 1. Cydooctene was also transformed into fully deuterated cydooctene without a skeletal rearrangement. As shown in entries 2 and 3, saturated hydrocarbons have also been transformed into fully deuterated compounds. As described above, an interaction between allylic C-H bonds and palladium hydride induces the H-D exchange reaction for alkenes. H-D exchange in alkanes, however, cannot be explained in this way. Direct C-H activation without assistance from any functional group may be a route to the formation of fully deuterated alkanes. 

While Baeyer-ViHigcr oxidations of saturated ketones generally occur without skeletal rearrange-ments, heteiolytic cleavages may occur if cations are readily accessible. For example, ring a of triterpe-... 

Skeletal rearrangements of saturated hydrocarbons on CePd3 were studied by Le Normand et al. (1984). Hydrogenolysis of methylcyclopentane, isomerization of 2-methyl-pentane and aromatization of 3-methylhexane were performed at 350 or 360°C. The results were compared with those of classical Pd/Al203, Pd/Si02 or Pd/Ce02 catalysts. The activity of CePd3 itself was very low and palladium atoms seemed to play a minor role. For example, the initial reaction of methylcyclopentane was the selective formation of isopentane, which is not observed on classical palladium catalysts. Air treatment at... 

In other reactions, like skeletal rearrangements of saturated hydrocarbons, the decomposition of CePd3 into Pd and Ce02 was also found to increase its activity by two orders of magnitude with an enhanced selectivity towards aromatization and 1-5 ring closure (Le Normand et al. 1984). 

Investigations which concern the mechanisms of skeletal rearrangements of saturated hydrocarbons induced by heterogeneous transition metal catalysis are of great interest for industrial applications, e.g. for petroleum reforming processes The developments in this field were reviewed recently by Hejtmanek, and by Maire and Garin , who focussed on the probable reaction mechanisms which include bond-shift and cyclic mechanisms for the skeletal isomerization of acyclic alkanes. Scheme 1 summarizes the... 

It is generally admitted that skeletal transformations of hydrocarbons are catalyzed by protonic sites only. Indeed good correlations were obtained between the concentration of Bronsted acid sites and the rate of various reactions, e g. cumene dealkylation, xylene isomerization, toluene and ethylbenzene disproportionation and n-hexane cracking10 12 On the other hand, it was never demonstrated that isolated Lewis acid sites could be active for these reactions. However, it is well known that Lewis acid sites located in the vicinity of protonic sites can increase the strength (hence the activity) of these latter sites, this effect being comparable to the one observed in the formation of superacid solutions. Protonic sites are also active for non skeletal transformations of hydrocarbons e g. cis trans and double bond shift isomerization of alkenes and for many transformations of functional compounds e.g. rearrangement of functionalized saturated systems, of arenes, electrophilic substitution of arenes and heteroarenes (alkylation, acylation, nitration, etc ), hydration and dehydration etc. However, many of these transformations are more complex with simultaneously reactions on the acid and on the base sites of the solid... 

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