Deuterium ethane

Fig. 1. The percentages of the various ethanes observed during the exchange of an 8 1 deuterium ethane mixture on 3.0 mg. of rhodium at 42.7° C. , CjHe A, j C2HsDs j Cl, CjH2ll4 O, C2Hr)j j C2r)a. Xhe percentage of C2H6D was too small to be measured accurately.

Common Name(s) Monoxide Chlorine Deuterium Ethane... 

Even isotopes qualify as different substituents at a chirality center. The stereochemistry of biological oxidation of a derivative of ethane that is chrial because of deuterium (D = H) and tritium (T = H) atoms at carbon, has been studied and shown to... 

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-... 

In the case of CH3CHO the equilibrium is found to lie right over in favour of aldol. The forward reaction of step (2) and the reversal of step (1) are essentially competing with each other for the carbanion (87). Carrying out the reaction in DzO fails to result in the incorporation of any deuterium into the CH3 group of as yet unchanged ethanal, however, so that step (2) must be so much more rapid than the reverse of step (1) as to make the latter virtually irreversible. 

Since deuterium addition to ethylene yields C2H4D2, both of the last steps are irreversible and (13) can be taken as the rate-determining step. Accordingly, if all prior steps are at equilibrium, we can write for the rate R of ethane formation ... 

A mixture of Pt(ll) and metallic Pt in an aqueous medium was shown to oxidize ethane to yield acetic and glycolic acids. A series of deuterium-exchange processes enabled a complex mechanism to be elucidated metallic platinum catalyzes the oxidation of intermediate alcohols to acid products, whereas the Pt(ll) salt activates the initial alkene (Scheme 7X29... 

The rate of ethane formation in ethanol dehyration (C2H5OH — C2H4 + H20) on the Nb dimer/Si02 catalyst is accelerated 1.7 times when C2H5OH is replaced by C2D5OH. The substitution of the OH hydrogen with deuterium gives no effect on the rate. Explain the inverse isotope effect. 

One such typical transformation is the thermal isomerization of the spiropentane derivative 76 into triene 80 which is assumed to occur via the diene intermediate 78 with the intermediate participation of the cyclopropyl-trimethylenemethane (TMM) 77 and the vinyl-TMM 79 diradicals (equation 29)44. It was shown by using deuterium labels that the diradical 79 forms the triene 80 by 1,6-hydrogen shift. The pathway 76 — 80 which occurs via tetramethylene-ethane diradical was recognized as a less probable route. 

Studies in deuterated water have shown that the hydroxyl proton does not end up in the ethanal formed. The decomposition of the 2-hydroxyethyl is not a simple P-elimination to palladium hydride and vinyl alcohol, which then isomerises to ethanal. Instead, the four protons stemming from ethene are all present in the initial ethanal product [6] (measured at 5 °C in order to suppress deuterium/hydrogen exchange in the product) and most authors have therefore accepted an intramolecular hydride shift as the key-step of the mechanism (see Figure 15.2). There remains some doubt as to how the hydride shift takes place. 

Electron-rich iridium(l) complexes can perform C—H activation reactions under mild conditions [13]. In this line, acetone-dis solutions of the [(ri -l,3,5-C 5H3Me3)) lr(Ti -C2H4)(P Pr3)]BF4 complex, at room temperature, show deuterium incorporation to the ethane ligand, most likely due to the participation of hydrido vinyl iridium(lll) species, formed by the C—H activation of ethane, according to Scheme 2.25 [21]. 

Many mechanistic implications have been discussed, but we will concentrate here only on the most important structures in the context of dihydrogen-cation complexes. Deuterium-labeled methane and methyl cations were employed to examine the scrambling and dissociation mechanisms. The protonated ethane decomposition yields the ethyl cation and dihydrogen. Under the assumption that the extra proton is associated with one carbon only, a kinetic model was devised to explain the experimental findings, such as H/D scrambling. ... 

Similar results have been obtained for methane 12) and for ethane 19). The values quoted in Table II also illustrate the point that the distribution of deuterium between hydrogen and propane differs from the value expected for a random distribution. With the ratio of pressures used, the expected percentage for the mean deuterium content of the hydrocarbon would be 33.3, which is substantially less than the experimental value of 40.9 %. This type of deviation is also found with other hydrocarbons, but it does not affect the validity of using classical theory for the calculation of the interconversion equilibrium constants in studies of mechanism of exchange reactions. More accurate values for these equilibrium constants are necessary, however, if one is interested in the separation of isotopes by chemical processes. 

It is important to understand why this apparent first-order behavior is found for the course of an exchange reaction with time whatever the true kinetics of the reaction. A failure to understand this feature of exchange reactions has sometimes led to unjustifiable statements about the ratedetermining step in such reactions. It is convenient to discuss a specific example—the exchange of ethane with deuterium. Suppose that the only adsorbed species taking part in the reaction are (a) physically adsorbed... 

We shall now consider in outline a general method devised by Anderson and Kemball (19) for the interpretation of the initial distributions of products obtained in multiple-exchange processes. The method was devised, in the first instance, to apply to the exchange of ethane and deuterium, but it can be extended quite simply to cover other types of molecules. It involves the adoption of a specific mechanism from which calculated distributions are then obtained for comparison with observed distributions. The method will be illustrated for the exchange of ethane. The mechanism adopted is as follows. 

Adsorbed ethyl radicals are formed by the dissociative adsorption of ethane. Every ethyl radical may either leave the surface with a deuterium atom to form an ethane molecule or lose one of the three hydrogen atoms of the methyl group to form adsorbed ethylene. The chances of these two events are 1/(1 + P) and P/(l -f P), respectively, P being a constant for a given catalyst. Equal chance is assumed for the loss of each of the three hydrogen atoms of the methyl group in the second process. 

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