Olefins technical oxidations

Olefin metathesis is the transition-metal-catalyzed inter- or intramolecular exchange of alkylidene units of alkenes. The metathesis of propene is the most simple example in the presence of a suitable catalyst, an equilibrium mixture of ethene, 2-butene, and unreacted propene is obtained (Eq. 1). This example illustrates one of the most important features of olefin metathesis its reversibility. The metathesis of propene was the first technical process exploiting the olefin metathesis reaction. It is known as the Phillips triolefin process and was run from 1966 till 1972 for the production of 2-butene (feedstock propene) and from 1985 for the production of propene (feedstock ethene and 2-butene, which is nowadays obtained by dimerization of ethene). Typical catalysts are oxides of tungsten, molybdenum or rhenium supported on silica or alumina [ 1 ]. 

In summary, catalytic C-H transformations in small unfunctionalized alkanes is a technically very important family of reactions and processes leading to small olefins or to aromatic compounds. The prototypical catalysts are chromia on alumina or vanadium oxides on basic oxide supports and platinum on alumina. Reaction conditions are harsh with a typical minimum temperature of 673 K at atmospheric pressure and often the presence of excess steam. A consistent view of the reaction pathway in the literature is the assumption that the first C-H abstraction should be the most difficult reaction step. It is noted that other than intuitive plausibility there is little direct evidence in heterogeneous reactions that this assumption is correct. From the fact that many of these reactions are highly selective toward aromatic compounds or olefins it must be concluded that later events in the sequence of elementary steps are possibly more likely candidates for the rate-determining step that controls the overall selectivity. A detailed description of the individual reactions of C2-C4 alkanes can be found in a comprehensive review [59]. 

Glycol derivatives, e.g., 2-chloroethanol (eq. (31)) are to a small extent byproducts in the technical olefin oxidation. With a very high concentration (ca. 5 mol/L) of cupric chloride and high pressure, 2-chloroethanol is the main product of ethylene oxidations, besides some acetaldehyde [33]. Cupric chloride is essential. In its absence, in spite of a high chloride ion concentration absolutely no 2-chloroethanol is obtained. It is assumed that analogously to acetaldehyde formation a y9-hydroxyethyl species bonded to a bi- or oligo-Pd-Cu cluster is an intermediate from which 2-chloroethanol is liberated by reductive elimination. 

As a matter of fact, olefin-consuming reactions (by H2) may be a serious problem in some technical reactions. Palladium complexes and Co2(CO)g (commercial products) are typical catalysts. Problems may also arise in the Fischer-Tropsch reaction [19, 20] where iron oxides of a certain basicity (alkaline-metal doping) are being used to catalyze the formation of hydrocarbons according to (the simplified) eq. (15). More details are provided in Section 3.1.8. Since water is inevitably formed, carbon dioxide can also occur. On the other hand, it is doubtful whether the CO/H2O system will be used for directed reductions of organic compounds, since hydrogen is an extremely abundant industrial chemical. The water-gas shift reaction is thus to be avoided in the vast majority of cases. 

In contrast to the catalysts containing Ti that produce polymers with a broad MW distribution of 5 to 30, the compounds containing V produce polyethylene with a narrow MW distribution of 2-4. The V systems are suited to polymerization of higher a-olefins and for copolymerization. Therefore, these systems are used technically to make a rubber (EPDM type) by copolymerization of C2H4, propylene, and as diene ethylidene norbor-nene (ENB). These catalysts are initially very active because of the presence of V(III), which seems to be the active oxidation form. However, some of them lose activity by reduction after a short polymerization time. They can be reactivated by weak oxidizing agents (activator) like chlorobenzene. 

Higher Olefins. Yapor-phase oxidation of olefins in the presence of vanadium pentoxide catalysts results in substantial yields of maleic anhydride which increase with increase in molecular weight of the olefin. Thus, from pentene-2, trimethylethylene, technical amylene, methyl pen-tene, heptene, and octene, approximate relative conversions of 10, 25, 27, and 30 per cent, respectively, were obtained from 5, 6, 7, and 8 C-atom olefins. Optimum tanperatures of about 425 C were foimd for amylene oxidation. Catalysts used for 250 hr showed no reduction in activity. 

The oxidation of olefins to carbonyl compoimds (the Wacker process in technical concerns, also called the Hoechst-Wacker process) was of great importance for the recognition of the usefulness of organometalhc homogeneous catalysis in the bulk chemicals industry [32]. The Wacker ethylene oxidation is one of the key steps in industrial homogeneous catalysis. Palladium catalysts are usually applied and have... 

Also, the final oxidation of the formyl group adds further economic and technical difficulties to the hydroformylation route. More attractive in the respect could be therefore the Pd-catalyzed asymmetric hydrocarboxylation of the same olefinic... 

A 1.1 Technically, the bromine number is the number of grams of bromine reacting with 100 g of the sample under prescribed conditions. By this definition, bromine consumed by addition, substitution, oxidation, and reactions with sulfur, nitrogen, and oxygen-containing compounds is included in the bromine number of the material. The use of the bromine number under determination in the estimation of olefinic unsaturation depends on the fact that the addition reaction proceeds rapidly and completely under most conditions. The addition of bromine proceeds readily at temperatures down to or below 0 C. Decreasing temperature of reaction, time of contact, and concentration of free bromine... 

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