Exchange reactions, multipl

A few plants are designed to produce styrene from EB but as a coproduct with propylene oxide (PO). In this process, EB is oxidized to a hydroperoxide (A in Figure 8—8) by bubbling air through the liquid EB in the presence of a catalyst. Hydroperoxides are, by their nature, very unstable compounds (one of the reasons that bleach, another hydroperoxide, works so well). So exposure to high temperatures has to be limited. The reactions are usually run at about 320°F and 500 psi pressure. Heat exchangers and multiple vessels are used to control the temperatures. Pressures are not critical in this process. 

Metals which with adsorbed CO prefer to form metal-carbon bonds on the summits are Pt and Ir (Cu ) metals which promote binding in the valley are Pd > Ni > Rh, Re. Metals promoting multiple metal-carbon bonds (with hydrocarbons) are Ni, Ru, Rh Pt and Pd are much worse in this respect. Let us extrapolate and assume that what holds for CO also holds for hydrocarbon molecules, and that the characterization of the multiple-bond formation propensity is valid also at higher temperatures than were established experimentally by exchange reactions. Then we can attempt to rationalize the available information on the formation and the role of various hydrocarbon complexes. 

F. A Theory for Calculating the Initial Distributions of Products in Multiple Exchange Reactions. 238... 

Multiple Exchange Reactions, An exchange reaction in which more than one deuterium atom is introduced into the hydrocarbon molecule on each interaction of the molecule with the catalyst is classified as a multiple exchange reaction. The existence of such a process may be recognized in three ways, exactly analogous to those described above for simple exchange reactions ... 

In the study of multiple exchange reactions, it is desirable to work with a high ratio of deuterium to hydrocarbon. This minimizes the influence of isotopic dilution of the deuterium on the rate of production of the more highly deuterated species during the early part of the reaction. The use of deuterium containing as small a percentage of hydrogen as possible is also important if true initial distributions of products are to be obtained. 

Multiple Exchange Reactions. The possible mechanisms which may lead to multiple exchange are necessarily more complicated than those responsible for simple exchange. Four alternatives may be considered. 

The determination of whether the multiple exchange occurs by an a-a, a-/3, or a-y process is obviously an important step in the elucidation of the mechanism. Careful examination of the initial distributions of products can be most useful both in this connection and in providing evidence about the types of adsorbed species responsible for the exchange reaction. This examination may be carried out in two ways, either (a) the comparison... 

Both 49 and trialkylsilanes undergo exchange reactions with trimethylhalosilanes in the presence of quinoline to give 1-halosilatranes (equation 73)16. It is likely that steric hindrance is responsible for the lack of addition of 1-hydrosilatrane (49) to the multiple bond of monosubstituted alkenes and acetylenes in the presence of H2PtCl6 or under UV... 

Lopshire [188] explored the exchange reaction of chlorine by oxygen with polychlorobiphenyl anions as a method of compound-selective polychloro-biphenyl congener detection in a gas chromatography-mass spectrometric system. Multiple reaction monitoring allowed separate chromatograms to be detected for each different polychlorobiphenyl composition from tetra-through nonachloro. 

It is very likely that the different adsorption modes as shown in Figure 1 are influenced differently by changes in temperature and partial pressure of reactants. The same holds for the influence of support induced changes in the electronic properties of the metal on the adsorption of the various intermediates. Instead of using the multiplicity, one should carefully analyze the observed selectivities and extract the contribution of the different adsorption modes in the exchange reaction. D1 represents the contribution of the G-T)1 intermediate. By using the developed Monte-Carlo model, the contribution to the formation of D2 of the di-G-46... 

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