The hydrogenation of cyclopropane

The metal-catalysed hydrogenation of cyclopropane has been extensively studied. Although the reaction was first reported in 1907 [242], it was not until some 50 years later that the first kinetic studies were reported by Bond et al. [26,243—245] who used pumice-supported nickel, rhodium, palladium, iridium and platinum, by Hayes and Taylor [246] who used K20-promoted iron catalysts, and by Benson and Kwan [247] who used nickel on silica—alumina. From these studies, it was concluded that the behaviour of cyclopropane was intermediate between that of alkenes and alkanes. With iron and nickel catalysts, the initial rate law is 

Throughout these studies, no product other than propane was observed. However, subsequent studies by Sinfelt et al. [249—251] using silica-supported Group VIII metals (Co, Ni, Cu, Ru, Os, Rh, Ir, Pd and Pt) have shown that, in addition to hydrogenation, hydrocracking to ethane and methane occurs with cobalt, nickel, ruthenium and osmium, but not with the other metals studied. From the metal surface areas determined by hydrogen and carbon monoxide chemisorption, the specific activities of 

Activation energies observed in the hydrogenation of cyclopropane over various metals 

254] from their studies of cyclopropane hydrogenation and hydrocracking over evaporated nickel films and nickel powders, and by McKee [255] for the platinum-catalysed reaction. 

In a detailed kinetic study, Sridhar and Ruthven [256], using nickel supported on Kieselghur (58% Ni), alumina (14% and 40% Ni) and silica-alumina (5% Ni), showed that over all four catalysts the rates of both hydrogenation and hydrocracking could be correlated according to the power rate law equation 

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The three carbon atoms of the cyclopropane ring lie in a plane. Therefore the angle strain is expected to be considerable because each C-C-C valence angle must be deformed 49.5° from the tetrahedral value. It is likely that some relief from the strain associated with the eclipsing of the hydrogens of cyclopropane is achieved by distortion of the H-C-H and H-C-C bond angles ... 

The results, presented in Fig. 10, are very similar to those already discussed for ethylene and ethane. Reaction (I), the hydrogenation of cyclopropane, has been shown earlier to be structure insensitive (103a, 103b). The activity pattern of this reaction is reminiscent of cyclohexane dehydrogenation (63). Initially, a small increase in activity is found, followed at 80% Cu by a rapid decline. These results show that reaction (II) is of the hydrogenolysis type and that reaction (I) is hydrogenation of an unsaturated bond. 

Figure 15 Effect of particle size on the turnover number for the hydrogenation of cyclopropane and of cyclopentane (x, ref. 311 , ref. 3 o,ref. 316)...

In Fig. 10, curves 1 and 3 represent the hydrogenation of cyclopropane over Pt. The shapes are similar, but curve 2, for nickel, shows a maximum TOF at a d of about 1.2 nm, the lowest value used for the platinum data. 

The hydrogenation of cyclopropane is to be carried out on a Pt/Si02 catalyst at 0°C. This is a prototype study for control of some higher molecular weight atmospheric pollutants in which the cyclopropane ring is thought to control both reactivity and transport properties. The porosity of the proposed catalyst is 0.45, its bulk density is 1.2g/cm, and... 

The hydrogenolyaia of cyclopropane rings (C—C bond cleavage) has been described on p, 105. In syntheses of complex molecules reductive cleavage of alcohols, epoxides, and enol ethers of 5-keto esters are the most important examples, and some selectivity rules will be given. Primary alcohols are converted into tosylates much faster than secondary alcohols. The tosylate group is substituted by hydrogen upon treatment with LiAlH (W. Zorbach, 1961). Epoxides are also easily opened by LiAlH. The hydride ion attacks the less hindered carbon atom of the epoxide (H.B. Henhest, 1956). The reduction of sterically hindered enol ethers of 9-keto esters with lithium in ammonia leads to the a,/S-unsaturated ester and subsequently to the saturated ester in reasonable yields (R.M. Coates, 1970). Tributyltin hydride reduces halides to hydrocarbons stereoselectively in a free-radical chain reaction (L.W. Menapace, 1964) and reacts only slowly with C 0 and C—C double bonds (W.T. Brady, 1970 H.G. Kuivila, 1968). 

In other cases, sulfenic acid elimination can involve y-hydrogen atoms with the formation of cyclopropane derivatives. y-Klimination is favored when DMSO is the reaction solvent. An example involving l-methylsulfinyl-2-ethyl-3-phenyl propane [14198-15-3] is shown in equation 13 (45) ... 

The catalyst exerts some influence on the bonds broken in hydrogenolysis of saturated cyclopropanes (775), but in vinyl and alkylidene cyclopropanes the effect is pronounced. Platinum or palladium are used frequently. In one case, Nishimura s [124a) catalyst, rhodium-platinum oxide (7 3), worked well where platinum oxide failed (.75). An impressive example of the marked influence of catalyst is the hydrogenation of the spirooctane 42, which,... 

In addition to a-additions to isocyanides, copper oxide-cyclohexyl isocyanide mixtures are catalysts for other reactions including olefin dimerization and oligomerization 121, 125, 126). They also catalyze pyrroline and oxazoline formation from isocyanides with a protonic a-hydrogen (e.g., PhCH2NC or EtOCOCHjNC) and olefins or ketones 130), and the formation of cyclopropanes from olefins and substituted chloromethanes 131). The same catalyst systems also catalyze Michael addition reactions 119a). 

The interaction of cyclopropane with clean surfaces of several metals was studied in our laboratory (42-46), and it was shown that at 273°K self-hydrogenation occurred, resulting in products strongly dependent on the nature of the metal. This conclusion followed from the indirect estimation of the average composition of the chemisorbed layer, based on the mass spectrometric analysis of the gas phase. Furthermore, the products... 

Fig. 18. Product distribution from the reaction of cyclopropane with hydrogen as a function of sulfur coverage over a Ni(l 11) catalyst. Temperature = 550K. Total pressure = 100 torn Hj/cyclopropane = 100. From Ref. 4.)...

The photodecomposition of -alkanes at excitation energies slightly above the absorption onset involves both C-H and C-C bond decompositions [18]. The dominant process is the C-H scission, (H2) 0.8-0.9, and the contribution of C-C decomposition is small. In the photolysis of cyclohexane, cycloheptane, cyclooctane, and cyclodecane, however, only hydrogen evolution was observed [[Pg.375]

The NMR spectra of cyclopropanes are unique among carbocycles. The HNMR chemical shift (c>H) of cyclopropane is 0.12, considerably upheld from cyclohexane (1.44), whereas the hydrogens of cyclobutane resonate further downheld (1.96).110 Similarly, upheld 13C chemical shifts (<>c) are found for cyclopropane (— 2.9), compared with cyclohexane (27) and cyclobutane (23.). 11... 

Relatively few studies of the hydrogenation of substituted cyclopropanes are extant. From the studies which have been reported [26,248, 258], it would appear that, with alkyl-substituted cyclopropanes, ring cleavage occurs by rupture of the bond opposite the carbon atom carrying the greatest number of substituent groups. Thus in the platinum on... 

The activity enhancement of MeFSM-16 by sulfiding with hydrogen sulfide in the isomerization of cyclopropane at 150°C... 

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