Propylene epoxidation materials

Shortly after the initial foray into the use of microporous titanosilicates as the highly dispersed Ti-supports for propylene epoxidation, interest shifted to meso-porous titanosilicates. Mesoporous Ti-containing materials are similar to micro-porous materials in that they offer highly dispersed Ti centers and reasonably well-defined tetrahedral Ti sites incorporated in a silicious framework. Moreover, the existence of a mesoporous pore system of sufficient dimensions to incorporate Au species in the range of 2 nm allows for Au entities to access essentially the entirety of the support surface area and enhances transport of reactants and products to and from the sites. 

While MCM-41- and 48-based materials dominate as the primary mesoporous materials explored for gas-phase propylene epoxidation, a recent article examines the reactivity of Au deposited on Ti-TUD containing 3 mol% Ti [57]. Ti-TUD consists of a sponge-like structure with an average pore size of about 13 run. Although the specific surface area of this material is less than that of MCM-41 or MCM-48, the larger pore system allowed for essentially all of the deposited Au to have access to the pore system. A maximum rate of 53.7 gpo kgcat 470 °C... 

Both academic and industrial research and development, as well as cooperation between industries, has resulted in a large effort in the discovery, synthesis, and catalytic application of framework metal-containing zeotype materials. These collaborations have led to new appHcations of metal-containing zeotype materials for the large-scale production of chemicals without major by-product formation. New environmentally friendly processes such as propylene epoxidation, phenol hydroxylation, ammoximation of cyclohexanone, and aromatization of light paraffins have been commer-ciahzed. Many new developments are in the pipehne, and they will Hkely be commerciahzed when both the economics and the environmental requirements become favorable. 

Many researchers have observed that the Au/TiOg catalysts rapidly deactivated, typically within one hour. Deactivation can be prevented, if the TiOg is supported on SiOj, or if TS-1 is used as the support. However, if a silicalite-derived material containing Ti (TS-1) is used as the support material, the preparation method of the support itself appeared to also largely affect the activity. A combined SEM and TEM study was conducted to analyze the various catalysts and to obtain insight into the reasons for the low activity in propylene epoxidation of some catalysts, and the high activity and selectivity of others. 

Poly(propylene carbonate) (PPC) is a biodegradable aliphatic polycarbonate that is synthesized from carbon dioxide and propylene epoxide. It is an amorphous polymer with Tg at about 20 °C that can be used as a toughening agent [148-150]. Both, PLA and PPC were reported to be compatible materials adding PLA to PPC... 

In 1957, it was discovered that organometaUic catalysts gave high mol wt polymers from epoxides (3). The commercially important, largely amorphous polyether elastomers developed as a result of this early work are polyepichlorohydrin (ECH) (4,5), ECH—ethylene oxide (EO) copolymer (6), ECH—aUyl glycidyl ether (AGE) copolymer (7,8), ECH—EO—AGE terpolymer (8), ECH—propylene oxide (PO)—AGE terpolymer (8,9), and PO—AGE copolymer (10,11). The American Society for Testing and Materials (ASTM) has designated these polymers as follows ... 

The initiator usually constitutes less than 1% of the final product, and since starting the process with such a small amount of material in the reaction vessel may be difficult, it is often reacted with propylene oxide to produce a precursor compound, which may be stored until required [6]. The yield of poloxamer is essentially stoichiometric the lengths of the PO and EO blocks are determined by the amount of epoxide fed into the reactor at each stage. Upon completion of the reaction, the mixture is cooled and the alkaline catalyst neutralized. The neutral salt may then be removed or allowed to remain in the product, in which case it is present at a level of 0.5-1.0%. The catalyst may, alternatively, be removed by adsorption on acidic clays or with ion exchangers [7]. Exact maintenance of temperature, pressure, agitation speed, and other parameters are required if the products are to be reproducible, thus poloxamers from different suppliers may exhibit some difference in properties. 

Diols are applied on a multimilhon ton scale as antifreezing agents and polyester monomers (ethylene and propylene glycol) [58]. In addition, they are starting materials for various fine chemicals. Intimately coimected with the epoxidation-hydrolysis process, dihydroxylation of C=C double bonds constitutes a shorter and more atom-efficient route to 1,2-diols. Although considerable advancements in the field of biomimetic nonheme complexes have been achieved in recent years, still osmium complexes remain the most efficient and reliable catalysts for dihydroxylation of olefins (reviews [59]). 

The problem of the role of acidity in the oxidation reaction has been examined. To this end silicalites containing both Ti(IV) and Al(III),- or Fe(III) or Ga(III) have been synthesized [24-26] and used in the epoxidation of propylene. It is well known that trivalent elements introduced in the framework impart definite acidic character to the material. The results obtained under very similar experimental conditions are given in Table 2. 

Supported Au catalysts have been extensively studied because of their unique activities for the low temperature oxidation of CO and epoxidation of propylene (1-5). The activity and selectivity of Au catalysts have been found to be very sensitive to the methods of catalyst preparation (i.e., choice of precursors and support materials, impregnation versus precipitation, calcination temperature, and reduction conditions) as well as reaction conditions (temperature, reactant concentration, pressure). (6-8) High CO oxidation activity was observed on Au crystallites with 2-4 nm in diameter supported on oxides prepared from precipitation-deposition. (9) A number of studies have revealed that Au° and Au" play an important role in the low temperature CO oxidation. (3,10) While Au° is essential for the catalyst activity, the Au° alone is not active for the reaction. The mechanism of CO oxidation on supported Au continues to be a subject of extensive interest to the catalysis community. 

Epoxides can co-polymerize with CO2 to give aliphatic polycarbonates. The co-polymerization is one of the most promising methods to utilize GO2 as a Cl feedstock. The product polycarbonates have many potential applications because of their unique properties. For example, poly(propylene carbonate) (PPG) decomposes completely at 300 °G in any environment to leave a very small amount of ash. This feature makes it applicable to pore former for mesoporous carbon composites. Poly(cyclohexene carbonate) (PGG) has glass-transition temperature (Tg) of 115°G, higher than 35-40 °G of PPG, endowing the materials with properties very similar to polystyrene. ... 

Hence, in this work, we report the heterogeneization of this new chiral macrocycle onto micelle-templated silicate (MTS) surface by substitution of chlorine atom of previously grafted 3-chloropropyl chain. After A-alkylation of the tetraazamacrocycle with propylene oxide and metalation with Mn(lI)Cl2, the catalytic performance of the corresponding hybrid materials was evaluated in the heterogeneous enantioselective olefin epoxidation. 

For this reason, the two enantiomers of propylene oxide are commonly used as chiral pool starting materials. These epoxides react with the appropriate Giignard reagent to give either enantiomer of the sulcatol. 

Epoxides have occasionally been used in Friedel-Crafts reactions, and some interesting stereochemical observations have been made in this context. Quite unlike secondary alcohols which give almost fully racemized product, it has been shown that optically pure propylene oxide with AlCh and benzene gives optically pure 2-phenyl-1-propanol with inversion of configuration at the cleaved center. AlBrs leads to much lower levels of optical purity it was demonstrated that both starting material and product are optically stable to the reaction conditions, and therefore partial racemization is intrinsic to the mechanism with AlBrs. It is nonetheless clear from these and other results that even powerful Lewis acids do not assure reaction via simple planar carbenium ions. 

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