Deuterium propylene

The spectra of C3H6 and C3D6 show that chemisorption of propylene is dissociative, but they fail to identify which carbon-hydrogen bond is broken on adsorption. To this end the spectra of a number of deuterium-labeled propylenes were studied and compared. These results are summarized in abbreviated form in Table VI, which specifies the hydrogen fragment formed on adsorption the fragment was identified as an OH if a band appeared near 3593 cm-1 or as an OD if a band appeared near 2653 cm-1. In those cases where the spectrum changed with time the summary... 

Many research groups have attributed the isomerization to a series of additions and eliminations of a cobalt carbonyl hydride. However, it has been shown that aldehydes may be found with formyl groups attached to a carbon atom other than the two of the double bond even under non-isomerizing conditions. Piacenti and co-workers (44, 45) studied the hydroformylation of [l-14C]propylene and of a>-deuterated a-olefins. Even for a-olefins with chain lengths up to C6, the formyl group was attached to all possible carbon atoms in the product mixture. However, in the deuterated experiments, deuterium was present only on carbons 2, 3, and a) of the resulting aldehydes. These results were explained by pro-... 

Proper deuterium-labeling experiments involving (CD3)4Sn and [1,1,1,-10,10,10-D6]-2,8-decadiene confirmed that propylene is indeed the first-formed olefin, and its structure indicated that the methylidene and ethyl-idene moieties originated from Me4Sn and 2,8-decadiene, respectively. 

The use of isotopic tracers has demonstrated that the selective oxidation of propylene proceeds via the formation of a symmetrical allyl species. Probably the most convincing evidence is presented by the isotopic tracer studies utilizing, 4C-labeled propylene and deuterated propylene. Adams and Jennings 14, 15) studied the oxidation of propylene at 450°C over bismuth molybdate and cuprous oxide catalysts. The reactant propylene was labeled with deuterium in various positions. They analyzed their results in terms of a kinetic isotope effect, which is defined by the probability of a deuterium atom being abstracted relative to that of a hydrogen atom. Letting z = kD/kH represent this relative discrimination probability, the reaction paths shown in Fig. 1 were found to be applicable to the oxidation of 1—C3He—3d and 1—QH —1 d. 

The value of z was calculated from the distribution of deuterium and acrolein and found to be very close to the theoretical value. It was also noted that the distribution of deuterium in acrolein was the same regardless of which deuterated propylene was used as the starting material and that the deuterium was found only on the terminal carbon atoms of the product acrolein. 

The binding of alkenes to transition metals, to form n complexes or r 2 complexes or metallacyclopropanes, is a Lewis acid-Lewis base interaction that is made more elaborate by back bonding from the metal to the alkene. There are many examples of deuterium IEs on complexation. One that was studied extensively is the binding of ethylene, propylene, and 2-butene to Ag+, where the deuterated alkene binds more strongly.88 For example, Acd,=cd,/Ac[ i, [Pg.145]

Orchin and Roos (108) examined the isomerization of allylbenzene by HCo(CO)4 and DCo(CO)4 at ambient temperature and pressure. Both HCo(CO)4 and DCo(CO)4 catalyzed isomerization to propenylbenzene at the same rate, and when DCo(CO)4 was used as catalyst 5% of the propenylbenzene produced was found to contain a deuterium atom. Hydroformylation of propylene with residual DCo(CO)4, after an isomerization of allylbenzene, yielded RCDO with no detectable RCHO. The authors chose to reject a mechanism involving addition of D—Co to the olefinic double bond, on the grounds that the lack of an isotope effect indicated breaking of D—Co, or H—Co, was not the rate-determining step, and that only a relatively minor amount of deuterium was incorporated into the isomerized reaction product. Instead, the authors favored a mechanism expressed as... 

Studies with specifically deuterium labeled 2-propanols also indicated that this was a contributing pathway. In situ generation of propylene necessarily must result in loss of one [I deuterium from the isopropyl precursor. Under the conditions employed for these labeling studies, the hydride would be derived from HI (as opposed to DI), so that such an overall reaction would be expected to result in loss of one fi deuterium in going from isopropyl... 

Katzer (28) observed that counterdiffusion of benzene and cumene within the pores of H-mordenite does not occur at low temperatures. However, H-mordenite shows activity for the alkylation of benzene with propylene to form cumene under the liquid phase conditions used for the diffusion studies, and he has suggested that reaction must occur on the external crystallite surface, or just within the pore mouth. In earlier studies on the isomerization of 2,3-dimethylbutene-l at 0°-20°C over a deuterated Y-type faujasite (62), we observed that the extent of isomerization (2,3-dimethylbutene-2) was far greater than the extent of deutera-tion only a fraction of the total deuterium on catalyst OD groups was exchanged. One possible explanation—assuming a protonic isomerization mechanism—is that, because of lowered intracrystalline diffusion rates... 

In earlier work (52) we found that reaction between ethylene and deuterium on catalysts activated at high temperatures led to detectable formation of neither ethylene-d nor ethane-ds. Under similar conditions propylene-d and propane-da were formed in reaction between deuterium and propylene. We will assume for the moment that this situation would also obtain on chromias activated at lower temperatures. On this assumption, reversal of monoadsorbed alkane to adsorbed olefin is not a significant process. If it were, one would get exchanged ethylene. 

The most well accepted feature of the mechanism is the formation of an allylic intermediate via a-hydrogen abstraction from propylene in the ratedetermining step. The structure of this intermediate and its subsequent steps involved in its conversion to selective products are much less well understood. It has been suggested from deuterium-labeling studies (77) that this intermediate undergoes a second hydrogen abstraction followed by O (oxidation) or N insertion (ammoxidation) (Scheme 3). The formation of an... 

A preliminary study of the propylene-deuterium reaction over palladium-pumice (55) showed extensive olefin exchange the reaction has since been re-examined using palladium-alumina 31). The progress of the exchange reaction at — 20° is shown in Fig. 8, from which it appears... 

Fig. 8. Partial results of the course of reaction of propylene with deuterium over palladium-alumina at —20° (31).

Temp. rc) D,/C,H. Conversion (%) Propylene composition Propane composition o M H in deuterium (%)... 

Produet DietributioHS from the Reaction of Propylene wUh Deuterium over Planum Catalyele... 

Product Distributions from the Reaction of Propylene Ufith Deuterium over Iridium Catalysts (31)... 

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