Activation of Propylene

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 first step in the oxidation of propylene is the abstraction of a hydrogen atom from the methyl group of propylene, and because an isotope effect was observed for this process, this abstraction is the ratedetermining step. 

The hydrocarbon intermediate formed after abstraction of the methyl hydrogen is symmetrical and not cyclic because no deuterium is found on the middle carbon atom of acrolein. The structure of this intermediate is probably similar to a ir-allylic species, CH2 - CH. . . CH2, in which the terminal carbon atoms are rapidly equilibrated. 

Propylene undergoes two successive hydrogen abstractions before the addition of oxygen. 

The mechanism of propylene oxidation over bismuth molybdate and cuprous oxide is the same. 

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Fig. 12. The ratio between the activity of propylene polymerization catalysts and their specific surface. The specific surface of the samples was calculated from the average sizes of primary crystallites, determined by using X-ray techniques, on the assumption that the crystallites have the form of hexagonal prisms (001 axis). Polymerization at 70°C, cocatalyst AlEtjCl, monomer concentration 1 M. From Yermakov et at. (13).

A possible mechanism for the PEG6000(NBu3Br)2-catalyzed cycloaddition of C02 with epoxides is proposed as shown in Scheme 5.2. The proposed mechanism involves the activation of propylene oxide (PO) by the ammonium cation (step I), the ring opening of the epoxide via nucleophilic attack of bromine at the least-hindered carbon (step II), and the insertion of C02 into the N-O bond (step III). Subsequent cyclization via an intramolecular nucleophilic attack (step IV) leads to the propylene carbonate (PC) and the regeneration of the catalyst. 

Polymerization of propylene with complex 5 (Table 4) at atmospheric pressure produces an atactic polypropylene having the same features regarding the temperature and Al Zr ratio as for ethylene. The H and 13C-NMR spectroscopic analysis of polypropylene reveals only vinyl/isopropyl, but no vinylidene/n-propyl, end groups, similar to the polymers obtained with zirconocenes [67,68]. Polymers with these end groups may be formed from at least three different mechanisms. The first involves an allylic C-H activation of propylene, the second, a /1-methyl elimination, and the third, a /1-hydrogen elimination from a polymer chain in which the monomer inserts in a 2,1 fashion [69]. Since in the... 

One of the most interesting recent topics in ruthenium chemistry is undoubted ) C—H bond activation in which the generation of coordinatively unsaturated specie> may play an important role. These species are usually produced by thermal or photo-mediated reductive elimination of dihydrogen, alkanes, alkenes or arenes. Recently, dehydrochlorination from RuHCI(CO) (P BuTMe) is reported to give a 7C-allyl complex via C—H activation of propylene (eq (42)) [144]. 

The immobilized, colloidal palladium catalyst, Si02-(C3H6SH)nPd is reported to induce the Heck reaction [14a] between ethyl iodide and ethyl acrylate. XPS data showed the presence of Pd(Il) on the surface of the colloidal Pd particles, owing to air oxidation this explains the different behavior of this and the Pd/C catalyst. Addition of BujN.HI and iodine greatly reduced the induction period. The catalytic activity of propylene carbonate-stabilized palladium colloids in the Heck reaction has been investigated [14b]. 

Fig. 10. Effect of perovskite substitution on the activity of propylene oxidation. Redrawn from Ref. (65). Tis the temperature at which propylene oxidation rate is 10 mol/(m s).

The activity of propylene is only 1% of that of ethylene. Acetylene also accelerates ripening but only at substantially higher concentrations. 

The activity changes with the acidity. Figure 3.11 shows a nonlinear behavior of the activity with the acidity. Otherwise, the activity of propylene polymerization varies linearly with the acidity. 

Dilrr, H., Triplet-intermediates from diazo-compounds — Carbenes, Topics Curr. Chem., 55,87,1975. Figurea, J.M., Fernandez, E., and Avila, J., Photolysis of diazo-n-propane. A route for the photochemical activation of propylene, J. Phys. Chem., 78,1348,1974. 

Propylene Oxidation. The propylene oxidation process is attractive because of the availabihty of highly active and selective catalysts and the relatively low cost of propylene. The process proceeds in two stages giving first acrolein and then acryUc acid (39) (see Acrolein and derivatives). 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

Chemical Manufacturing. Chemical manufacturing accounts for over 50% of all U.S. caustic soda demand. It is used primarily for pH control, neutralization, off-gas scmbbing, and as a catalyst. About 50% of the total demand in this category, or approximately 25% of overall U.S. consumption, is used in the manufacture of organic intermediates, polymers, and end products. The majority of caustic soda required here is for the production of propylene oxide, polycarbonate resin, epoxies, synthetic fibers, and surface-active agents (6). 

Polymerization to Polyether Polyols. The addition polymerization of propylene oxide to form polyether polyols is very important commercially. Polyols are made by addition of epoxides to initiators, ie, compounds that contain an active hydrogen, such as alcohols or amines. The polymerization occurs with either anionic (base) or cationic (acidic) catalysis. The base catalysis is preferred commercially (25,27). 

Polyall lene Oxide Block Copolymers. The higher alkylene oxides derived from propjiene, butylene, styrene (qv), and cyclohexene react with active oxygens in a manner analogous to the reaction of ethylene oxide. Because the hydrophilic oxygen constitutes a smaller proportion of these molecules, the net effect is that the oxides, unlike ethylene oxide, are hydrophobic. The higher oxides are not used commercially as surfactant raw materials except for minor quantities that are employed as chain terminators in polyoxyethylene surfactants to lower the foaming tendency. The hydrophobic nature of propylene oxide units, —CH(CH2)CH20—, has been utilized in several ways in the manufacture of surfactants. Manufacture, properties, and uses of poly(oxyethylene- (9-oxypropylene) have been reviewed (98). 

There are other methods of preparation that iavolve estabhshing an active phase on a support phase, such as ion exchange, chemical reactions, vapor deposition, and diffusion coating (26). For example, of the two primary types of propylene polymerization catalysts containing titanium supported on a magnesium haUde, one is manufactured usiag wet-chemical methods (27) and the other is manufactured by ball milling the components (28). 

Polypropylene. There is an added dimension to the catalytic polymerization of propylene, since in addition to the requirement that the catalyst be sufficiently active to allow minute amounts of catalyst to yield large quantities of polymer, it must also give predominantly polypropylene with high tacticity that is, a highly ordered molecular stmcture with high crystallinity. The three stmctures for polypropylene are the isotactic, syndiotactic, and atactic forms (90) (see Olefin polya rs, polypropylene). 

AHyl chloride exhibits reactivity as an olefin and as an organic haHde. Its activity as a chloride is enhanced by the presence of the double bond, but its activity as an olefin is somewhat less than that of propylene. AHyl chloride participates in most types of reactions characteristic of either functional group ... 

Both fixed and fluid-bed reactors are used to produce acrylonitrile, but most modern processes use fluid-bed systems. The Montedison-UOP process (Figure 8-2) uses a highly active catalyst that gives 95.6% propylene conversion and a selectivity above 80% for acrylonitrile. The catalysts used in ammoxidation are similar to those used in propylene oxidation to acrolein. Oxidation of propylene occurs readily at... 

Rennard and Kokes (39) in their paper stated directly that their purpose was just to study the catalytic activity of palladium hydride in the hydrogenation of olefins, in this case ethylene and propylene. Kokes (39a) in his article recently published in Catalysis Reviews summarizes the results of studies on such catalytic systems. 

A. Kaloyannis, and C.G. Vayenas, Non-Faradaic electrochemical modification of catalytic activity. 12 Propylene oxidation on Pt, J. Catal. 182, 37-47 (1999). 

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