Formation of ethane

Isomerization, disproportionation, and decomposition reactions of the radical Ri yield nonsaturated end groups CH2=CH—CH2 and result in the formation of ethane and ethylene. Isomerization and decomposition... 

The fact that both heats of formation and equilibrium pressures of the hydrates of spherical molecules correctly follow from one model must mean that the L-J-D theory gives a good account of the entropy associated with the motions of these solutes in the cavities of a clathrate. That the heat of formation of ethane hydrate is predicted correctly, whereas the theoretical value of its vapor pressure is too low, is a further indication that the latter discrepancy must be ascribed to hindered rotation of the ethane molecules in their cavities. 

Participation of adsorbed intermediates can also be shown by the prolonged decay of the potential 011 interruption of the current (Conway and Vijh, 1967a) or by measurement of the time-dependence of the formation of products by carrying out the reaction with pulses of potential of controlled duration (Fleischmann et al., 1966). Thus the formation of ethane in the Kolbe reaction of acetate ions in acid solutions is initially proportional to the square of time as would be predicted for the rate of the step (27) (Fleischmann et al., 1965). 

The photo-Kolbe reaction is the decarboxylation of carboxylic acids at tow voltage under irradiation at semiconductor anodes (TiO ), that are partially doped with metals, e.g. platinum [343, 344]. On semiconductor powders the dominant product is a hydrocarbon by substitution of the carboxylate group for hydrogen (Eq. 41), whereas on an n-TiOj single crystal in the oxidation of acetic acid the formation of ethane besides methane could be observed [345, 346]. Dependent on the kind of semiconductor, the adsorbed metal, and the pH of the solution the extent of alkyl coupling versus reduction to the hydrocarbon can be controlled to some extent [346]. The intermediacy of alkyl radicals has been demonstrated by ESR-spectroscopy [347], that of the alkyl anion by deuterium incorporation [344]. With vicinal diacids the mono- or bisdecarboxylation can be controlled by the light flux [348]. Adipic acid yielded butane [349] with levulinic acid the products of decarboxylation, methyl ethyl-... 

A preparation of the third nitrogenase from A. vinelandii, isolated from a molybdenum-tolerant strain but lacking the structural genes for the molybdenum and vanadium nitrogenases, was discovered to contain FeMoco 194). The 8 subunit encoded by anfG was identified in this preparation, which contained 24 Fe atoms and 1 Mo atom per mol. EPR spectroscopy and extraction of the cofactor identified it as FeMoco. The hybrid enzyme could reduce N2 to ammonia and reduced acetylene to ethylene and ethane. The rate of formation of ethane was nonlinear and the ethane ethylene ratio was strongly dependent on the ratio of nitrogenase components. 

Moreover, while the change from cyclohexane to hexane as the reactant has produced a large change in the relative selectivity of the methane/pentane co-products with respect to other products, the ratio of propane to the ethane/butane couple is very close (46/30 or 1.5 for hexane and 24/20 or 1.2 for cyclohexane. Table 8). This small variation compared with the very large change in (methane + pentane) selectivity (18% for n-hexane, 56% for cyclohexane) suggests that the formation of ethane/butane is independent of the formation of methane/pentane, that is that intermediate E is not a major contributor to the formation of the ethane/butane couple. 

The formation of products is explained by the free radical mechanism, where the initiation step and the primary formation of ethane are described by the following equations ... 

Selective formation of ethane in this reaction is of key interest, since one of the major reasons for investigating homogeneous systems was the hope of achieving such selectivity. 

A treatment similar to that for unimolecular reactions is necessary for recombination reactions which result in a single product. An example is the possible termination step for the mechanism for decomposition of C Hg, H + CjH - (Section 6.1.2). The initial formation of ethane in this reaction can be treated as a bimolecular event. However, the newly formed molecule has enough energy to redissociate, and must be stabilized by transfer of some of this energy to another molecule. 

In Reference 17 Penczek alleges erroneously that Meerwein et al., [18] had reported finding no ethane by GLC. On the contrary, Reference 18 contains the explicit statement that the formation of ethane was confirmed gasometrically (GLC was not available in 1958.)... 

DR. GEOFFROY Let me answer the last question first. I don t fully understand cis-methyl groups. When complexes containing those have been irradiated, one generally doesn t observe the formation of ethane. Instead, where the chemistry is well-defined, it looks as if solvolysis simply occurs to yield radicals. There are, however, some cases of diaryl complexes which, when irradiated, will couple two phenyl ligands to give biphenyl as a product. 

From the methanol process we already learnt that propionic acid is one of the by-products. It stems from the formation of ethanal, which is hydrogenated... 

The formation of several volatile carbon hydrides in the hydrogen-graphite reaction between 360 and 800° was reported by Breisacher and Marx (138). The formation of ethane, ethylene, propylene, and even butane suggests that the edge of the carbon layers became hydrogenated in the first step of this reaction. The results were discussed on the basis of a mechanism proposal by Zielke and Gorin (139). 

As a consequence, it was necessary to work at complete conversion of propane to actually form 2 equiv. of ethane per mol of propane introduced and to determine carefuUy the mass balance. A study has been performed in a continuous flow reactor, under 50bar at 250°C with (=SiO)2Ta-H. After an initiation step (evacuation of the hydrogen evolved due to CH activation), the methane propane (1250 1) mixture leads under these conditions to the major formation of ethane indeed... 

Concerning the fact that Ci is always lower than C2, there is a simple explanation methane can only be formed by a positioning of zirconium on C-3 of the alkane whereas the formation of ethane comes from two possible coordination modes of the alkyl chain to zirconium in C-1 and in C-4 (Scheme 3.15). 

This hypothesis of secondary cleavage is confirmed in the hydrogenolysis of butane (Figure 3.22). At low conversion, one observes the formation of ethane. 

Termination. Various reactions between the possible pairs of radicals allow for the formation of ethane, CI2 or the methyl chloride. In this step, the reactive particles are consumed, but not generated. 

Souffie et al.20 have suggested that not only methane, but also a proportion of the ethane ( 7 A%) arises through reaction of hot methyl radicals, since addition of I2 does not entirely suppress the formation of ethane. They postulate the novel step ... 

Not observed were chloroethane (CH3-CH2C1) and vinyl chloride (CH2=CHC1). An interesting finding was that 1,1-DCA reacted much too slowly to represent an intermediate in the formation of ethane. The authors postulated a scheme involving successive one- or two-electron reduction steps to form radicals and carbenes to explain the absence of other observable intermediates, as well as the formation of products originating from radical or possibly from carbene coupling. Try to constmct such a hypothesized reaction scheme yourself. 

Fig. 24. Possible reaction scheme for the direct formation of ethane from adsorbed acetylene.

Reaction 1 is a terminating one, which accounts for the formation of ethane and probably methane connected with the appearance of the pic ... 

Stable complexes with Rh—CH2CH3 bonds similar to 19 have been well characterized. The final step is formation of ethane from 19 with regeneration of RhL3Cl ... 

Figure 24 The pathways discriminating between formation of ethane and evolution of...

In runs in which metallic platinum was not formed, the rate of formation of ethane was quite low or zero at temperatures above —10°, but at temperatures below —14° the rate was higher, falling off slowly with decreasing temperature. This is illustrated in Fig. 18. 

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