Cycloalkene, hydrogenation

Drivers Ibr Performing Cycloalkene Hydrogenation in Micro Reactors... 

Cycloalkene Hydrogenation Investigated in Micro Reactors Cas/liquid reaction 16 [CL 16] Catalytic hydrc enation of cydohexene... 

We report here the hydrogenation of cycloalkenes using Rh-incorporated montmorillonite as a catalyst. In our studies when hydrogenation experiments were carried out by employing binary mixtures of the olefins, considerable differences in hydrogenation behaviour were observed. It has been pointed out that the stereochemistry of cycloalkenes hydrogenation depends on the chemical and steric structure of the substrates, catalysts and reaction conditions [10]. 

When applying this principle to replacement names generated from fusion nomenclature, it is essential to keep in mind that fusion names for hydrocarbons ending in -cycloalkene are for fully unsaturated skeletons the -ene ending implies whatever number of double bonds may be necessary, without a multiplier. Thus (117) has six double bonds in the twelve-membered ring, and one must add ten hydrogens to saturate it to the stage of a simple benzene derivative, compound (118). 

Alkenes (Olefins) and Cycloalkenes. Olefins are unsaturated and highly reactive. Because of their propensity to be reduced to paraffins w ilh hydrogen or to merceptans with hydrogen sulfide, alkenes are found in petroleum only in very low concentrations. Single-ring cycloalkenes have the same formula, as olefins and so are difficult... 

Crotonaldehyde, hydrogenation of, 43-48 Cubane, isomerization of, 148 Cyclic dienes, metathesis of, 135 Cyclic polyenes, metathesis of, 135 Cycloalkenes, metathesis of, 134-136 kinetic model, 164 ring-opening polymerization, 143 stereoselectivity, 158-160 transalkylation, 142-144 transalkylidenation, 142-144 Cyclobutane configuration, 147 geometry of, 145, 146 Cyclobutene, metathesis of, 135 1,5,9-Cyclododecatriene, metathesis of, 135... 

The stereochemistry of hydrogenation of 1,2-dimethylcyclQhexene and 1,2-dimethylcyclopentene is instructive. Each of these substances would be expected to yield only the ci5-l,2-dimethylcycloalkane via cis addition. Both cis and trans isomers, however, are formed from either of these two cycloalkenes when hydrogenated in the liquid phase (acetic acid) over reduced platinum oxide—one of the more stereoselective catalysts [57, 58). The ratio of isomers which is produced is a function of the pressure of hydrogen, the proportion of cis increasing with increasing pressure (Fig. 5). This fact implies that the trans isomer is formed via a... 

IV. Conformational Analysis and the Geometry of the Pertinent Transition States in the Hydrogenation of Cycloalkenes... 

Although the transition state for the exchange reaction may be described as the critical complex for the conversion of the half-hydrogenated state to either a jr-complexed olefin or an eclipsed vicinal diadsorbed alkane, the stereochemistry of hydrogenation of cycloalkenes on platinum at low pressures can be understood if the transition state has a virtually saturated structure. 

Evidence derived from a study of the stereochemistry of hydrogenation of 1,2-cyclononadiene and 1,2-cyclodecadiene led Moore (108) to conclude that allyl complexes like those postulated above must be intermediates. He noted that, of the four ways in which either allene could be adsorbed on a surface, two, a and b, would yield via cis addition of hydrogen the cis-cycloalkene and two, c and d, the tram isomer. Examination of... 

Hussey et al. (109) have recently reported measurements of the kinetics of hydrogenation in the liquid phase of a large number of cycloalkenes, both individually and competitively. The data permit the kind of analysis... 

Structure effects on hydrogenation rate also have been studied in series of cycloalkenes. The influence of substituents on C=C is similar to that in aliphatic series (e.g., 52, 57, 90), but the point of interest is the observed... 

Isolated double bonds in alkenes and cycloalkenes are best reduced by catalytic hydrogenation. Addition of hydrogen is very easy and takes place at room temperature and atmospheric pressure over almost any noble metal catalyst, over Raney nickel, and over nickel catalysts prepared in special ways such as P-1 nickel [13] or complex catalysts, referred to as Nic [49]. 

Isomerizations may take place over some catalysts more than over others. Regio- as well as stereoisomers may be formed [13, 49. Such side reactions are undesirable in the reduction of pro-chiral alkenes, and especially in the hydrogenation of some cycloalkenes. 

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