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... 

Activation energies observed in the hydrogenation of cyclopropane over various metals... 

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. 

Walsh orbitals6 are the MOs corresponding to the cyclopropane C-C bonds. We begin by supposing that carbon orbitals are sp2 hybrid. Indeed, many studies show that cyclopropane is more like ethylene than propane or cyclobutane. For example, it adds bromine slowly, whereas cyclobutane is inert. Hydrogenation of cyclopropane occurs at 120°and cyclobutane at 200°. Asymmetric CH2 stretching modes appear in the IR spectrum of cyclopropane at 3050 and in that of ethylene at 3080 cm-1. Methyl cyclopropyl ketone shows a carbonyl stretch at 1695 cm-1. Finally, the HCH angle is 116°6 in ethylene, and 118° in cyclopropane. 

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)...

An example of the role of strongly bonded intermediates is afforded by the work of Ponec et al. (ifast reaction takes place only on a small fraction of the surface, whereas on the remainder the dissociated and dehydrogenated species are removed only slowly adsorption of both components is competitive. 

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... 

HYDROGENATION OF CYCLOPROPANES HAVING OTHER UNSATURATED GROUPS... 

Redaction by Hydrogen, Dissolving Metals, and Electrolysis. —Groger and Musso have found that under carefully selected reaction conditions the catalytic hydrogenation of cyclopropanes (low temperatures and often under pressure) always proceeds... 

Problem 4.17. According to Equation 4.16, hydrogenation of cyclopropane over a platinum catalyst results in ring opening and the formation of propane. Suppose the same reaction were carried out on methylcyclopropane. What product(s) might you expect to find ... 

---