Deuterium unsaturated hydrocarbons

The fact that an isotope effect of 1.7 0.1 is observed 38) in the benzene/deuterium oxide reaction at 30°C indicates that this reaction is the rate-determining step of the dissociative n complex substitution mechanism. In this respect the result agrees with the direct observations made by other investigators 41, 42), namely that unsaturated hydrocarbons chemisorb at a faster rate than their subsequent interactions with chemisorbed hydrogen. 

The use of several different experimental techniques to investigate a given system is likely to be particularly revealing. Two noteworthy examples in which stereochemical considerations had a part are provided by Taylor and Dibeler (8) on the reactions of deuterium with the butenes on nickel wires and by Meyer and Burwell (9, 10) on the deuteration of multiply unsaturated hydrocarbons. 

It has been observed [23,91,92] that when an unsaturated hydrocarbon is reacted with (a) equilibrated and (b) non-equilibrated hydrogen—deuterium mixtures, the deuteroalkane distributions are identical. Such observations indicate that the direct addition of a hydrogen molecule across the olefinic bond does not occur, and provides strong evidence for the formation of a half-hydrogenated state , that is, an adsorbed alkyl radical, first suggested by Horiuti and Polanyi [81], as a relatively stable reaction intermediate. The process of hydrogenation may thus be represented as... 

The second approach is that developed to interpret the products of the reactions of octalins with deuterium [144] and is equally applicable to the reactions of mono- or di-unsaturated hydrocarbons with deuterium. Smith and Burwell [144] pointed out that, whereas the experimental deuterohydrocarbon distributions are obtained in terms of the number of deuterium atoms in the product hydrocarbon, the quantities of fundamental importance to the discussion of the mechanisms of catalytic reactions are the fractions of the hydrocarbon sample which have equilibrated with the surface deuterium—hydrogen pool. Thus, for example, in the reaction of buta-1 3-diene with deuterium, the product butenes consist of a series of species, butene-(/i, d)2, -(h, d)3,..., -(h, d)n in which 2,3. .., n positions... 

M. Salmerdn and G.A. Somoijai. Desorption, Decomposition, and Deuterium Exchange Reactions of Unsaturated Hydrocarbons (Ethylene, Acetylene, Propylene, and Butenes) on the Pt(lll) Crystal Face. J. Phys. Chem. 86 341 (1982). 

The Exchange of Atoms between Deuterium Gas and Hydrides Exchange and Hydrogenation of Unsaturated Hydrocarbons The Fischer-Tropsch Synthesis. ... 

The patterns of behavior in catalysis by metals were mainly focused on hydrogenation of unsaturated hydrocarbons and deuterium exchange reactions. These reactions were performed in static systems. Evaporated metal films were widely used for these reactions but the problem was to get reproducible metal surfaces, in other words to have clean metal catalysts [2, 3]. 

R.L. Burwell Jr. to interpret the way in which unsaturated hydrocarbons interacted with deuterium (Section 8.3.5). 

The decarboxylation of carboxylic acid in the presence of a nucleophile is a classical reaction known as the Hunsdiecker reaction. Such reactions can be carried out sometimes in aqueous conditions. Man-ganese(II) acetate catalyzed the reaction of a, 3-unsaturated aromatic carboxylic acids with NBS (1 and 2 equiv) in MeCN/water to afford haloalkenes and a-(dibromomethyl)benzenemethanols, respectively (Eq. 9.15).32 Decarboxylation of free carboxylic acids catalyzed by Pd/C under hydrothermal water (250° C/4 MPa) gave the corresponding hydrocarbons (Eq. 9.16).33 Under the hydrothermal conditions of deuterium oxide, decarbonylative deuteration was observed to give fully deuterated hydrocarbons from carboxylic acids or aldehydes. 

It would be interesting to carry out analogous experiments with unsaturated alicyclic hydrocarbons whose side-chain is separated from the ring by a tertiary carbon atom. It would also be desirable to measure the kinetics of hydrogen exchange for non-equivalent atoms in alkene molecules, and to compare the rates of deuterium exchange and isomerization, and also the rates of all these processes in hydrocarbons of similar composition with double and triple bonds, and so on. 

Evidence from the kinetics of both olefin 27, 31) and acetylene 71) hydrogenation and from the exchange of cycloalkanes with deuterium 12) (in which 7r-allylic intermediates are formed) has shown almost unequivocally that molecular hydrogen can interact with adsorbed hydrocarbon species. When this is the case, addition takes place from above the axis of unsaturation. The importance of molecular hydrogen interaction, as a general phenomenon, has yet to be determined. However, the evidence is sufficiently strong to compel the consideration of steps such as... 

From the results we concluded that the dissociative mechanism originally suggested for the ethylene-deuterium exchange is valid and is responsible for the exchange involving other unsaturated, saturated and aromatic hydrocarbons and oxygenated compounds. 

A trispyrazolylborate platinum complex was found to activate C-H bonds via a Pt(ii)/Pt(iv) sequence. Removal of a methyl anion from [(77 -Tp )RhMe2] leads to an unsaturated species that then adds to the hydrocarbon C-H bond (Equation (12)). The related protonatcd species Tp PtMc2H loses methane at 110°G and then oxidatively adds benzene- 6. The new methyl-phenyl-deuteride derivative then reversibly exchanges deuterium into the methyl group, indicating reversible methane activation. In addition, the Pt-H bond can undergo reaction with oxygen to... 

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