Phase epoxidation

Liquid-Phase Epoxidation with Hydroperoxides. Molybdenum, vanadium, and tungsten have been proposed as Hquid-phase catalysts for the oxidation of the ethylene by hydroperoxides to ethylene oxide (205). tert- uty hydroperoxide is the preferred oxidant. The process is similar to the arsenic-catalyzed route, and iacludes the use of organometaUic complexes. 

B.S. Uphade, M. Okumura, S. Tsubota, and M. Haruta, Effect of physical mixing of CsCl with Au/Ti-MCM-41 on the gas-phase epoxidation of propene using H2 and02 Drastic depression of H2 consumption, Appl. Catal. A 190, 43-50 (2000). 

The latest industrial strides in PO synthesis are liquid phase epoxidation of propylene with H2O2 over TS... 

Currently there are four major lines of approach towards gas-phase epoxidation of propylene (1) mechanistic studies of Au/Ti02 catalysts through kinetics, spectroscopic identification of adsorbed species and... 

A heterogeneous olefin epoxidation catalyst containing both V and Ti in the active site was prepared by sequential non-hydrolytic grafting. The silica was exposed first to VO(OiPr)3 vapor followed by Ti(0 Pr)4 vapor. Formation of propene is evidence for the creation of Ti-O-V linkages on the surface. Upon metathesis of the 2-propoxide ligands with BuOOH, the catalyst becomes active for the gas phase epoxidation of cyclohexene. The kinetics of epoxidation are biphasic, indicating the presence of two reactive sites whose activity differs by approximately one order of magnitude. 

The stoichiometry and kinetics of gas phase epoxidation of cyclohexene by silica-supported Ti(0 Pr)4 upon treatment with /< r/-butyl hydro peroxide were the... 

The resulting material is active for the gas phase epoxidation of simple olefins. Addition of cyclohexene resulted in the formation of cyclohexene oxide as the sole volatile product, detected by GC/MS. 

Hydronium ion, 14 23 Hydroperoxidates, 18 411 Hydroperoxide process, for propylene oxide manufacture, 20 798, 801-806 Hydroperoxides, 14 281, 290-291 18 427-436 alkylation of, 18 445 a-oxygen-substituted, 18 448-460 chemical properties of, 18 430 433 decomposition of, 14 279 18 431-432 liquid-phase epoxidation with, 10 656 physical properties of, 18 427-430 preparation by autoxidation, 18 434 synthesis of, 18 433-435 Hydrophile-lipophile balance system,... 

All the results concerning the gas-phase epoxidation were obtained using HTE equipment, for all procedures involved, namely, the synthesis and testing of the Ag-based materials (Figure 11.27). 

A. K. Sinha, S. Sedan, S. Tsubota, and M. Haruta, A three-dimensional mesoporous titanosilicate support for gold nanoparticles Vapour-phase epoxidation of propene with high conversion, Angew. Chem. Int. Ed. 43(12), 1546-1548 (2004). 

T. Hayashi, K. Tanaka, and M. Haruta, Selective vapor-phase epoxidation of propylene over Au/Ti02 catalysts in the presence of oxygen and hydrogen, J. Catal. 178(2), 566-575 (1998). 

A. Zwijnenburg, M. Saleh, M. Makkee, and J. A. Moulijn, Direct gas-phase epoxidation of propene over bimetallic Au catalysts, Catal. Today 72(1—2), 59—62 (2002). 

A recent synthesis of the phenylisoserine side-chain of taxol is shown in Scheme 18. The enone 21 was obtained in high yield by condensation of benzal-dehyde with pinacolone. Employing the non-aqueous two-phase epoxidation protocol, epoxide 22 was obtained in 76% yield and 94% e.e. Recrystallisation of the epoxide furnished the desired enantiomer in 97 % e. e. Subsequent manipulations of the epoxy-ketone gave the taxol side-chain 23 with the required stereochemistry (Scheme 18). 

Gas electron diffraction (GED) acyl peroxides, 702 peroxynitrates, 743-4 see also Electron diffraction Gas-hqiud chromatography (GLC) hydroperoxide determination, 684-5 ozonide determination, 719 Gas-phase addition, hydroperoxides, 157 Gas-phase epoxidation, alkenes, 58 gauche arrangement, acyclic organic peroxides, 102, 104-5 GED (gas electron diffraction), 743-4 Geminal regioselectivity... 

Gas-phase epoxidation of propylene with 02/H2 mixtures was accomplished over Ag1267 or Au1268 catalysts dispersed on TS-1 or other Ti-containing supports and Ti-modified high-silica zeolites.1269 Sodium ions were shown to be beneficial on the selectivity of propylene epoxidation with H202 over titanium silicalite.1270 A chromia-silica catalyst is active in the visible light-induced photoepoxidation of propylene by molecular oxygen.1271... 

The epoxidation of propene is analogous to that of ethylene catalyzed by silver. However, the selectivity is much lower. Due to the pronounced oxidation sensitivity of the allyl CH3-group, excessive combustion occurs as a side reaction. The heterogeneous process has no practical significance, therefore, as it has to compete with a highly selective liquid phase epoxidation process. 

In the present work the synthesis of highly dispersed niobium or titanium containing mesoporous molecular sieves catalyst by direct grafting of different niobium and titanium compounds is reported. Grafting is achieved by anchoring the desired compounds on the surface hydroxyl groups located on the inner and outer surface of siliceous MCM-41 and MCM-48 mesoporous molecular sieves. Catalytic activity was evaluated in the liquid phase epoxidation of a-pinene with hydrogen peroxide as oxidant and the results are compared with widely studied titanium silicalites. The emphasis is directed mainly on catalytic applications of niobium or titanium anchored material to add a more detailed view on their structural physicochemical properties. 

In concomitance with the displacement observed by i.r., an evolution of the catalytic activity has been observed while studying the liquid-phase epoxidation of cyclohexene in the presence of (EGDA)- Mo(VI), freshly prepared or after four months of conditioning at room temperature under inert atmosphere. As usual, the appearance of epoxide was followed by gas chromatographic analyses or by direct titration of oxirane oxygen and the disappearance of hydroperoxide was monitored by iodometric titration. In figure we report concentration-time for typical runs in ethylbenzene at 80°C obtained with the experimental procedure already described (ref. 9). It may be seen that with a freshly prepared catalyst an induction period is observed which lowers the initial catalytic activity. Our modified Michaelis-Menten type model equation (ref. 9) cannot adequately fit the kinetic curves obtained due to the absence of kinetic parameters which account for the apparent initial induction period (see Figure). 

The two-phase epoxidation of alkenes by hydrogen peroxide in water-dichloromethane system, catalysed by manganese(III)-porphyrin, is strongly accelerated by addition of catalytic amounts of a carboxylic acid and lipophilic imidazole or pyridine axial ligand365,366. Manganese(III)-porphyrin bound to colloidal anion-exchange particles is more active in the selective epoxidation of styrene by aqueous hypochlorite than the same catalyst in aqueous solution367. 

Co2 + -exchanged faujasite zeolite is a unique heterogeneous catalyst for liquid-phase epoxidation using 02 [45]. This catalyst is active only for styrene, and the conversion and yield of styrene oxide were 65 and 45%, respectively. The TON, based on Co ions, reached 12. The Co2+ ions, located in supercages, are thought to cause activation of 02 for epoxidation. 

P 4] For preliminary investigations a small-scale micro structured reactor was used to perform gas-phase epoxidation of propylene to propylene oxide with evaporated H202. As catalyst titanium silicate (TS-1) was used. 

Thus, there may be an unlimited increase in selectivity by the elimination of free-radical intermediates. For example, selectivity of liquid-phase epoxidation with organic hydroperoxides depends on two factors [3] ... 

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