Palladium silica

Fig. 5. Adsorption isotherms and composition of the gas phase for the adsorption of ethylene on (a) rhodium—silica and (b) palladium—silica at 20°C. o, Total molecules adsorbed , ethylene , ethane.

Fig. 7. Adsorption isotherms for 14C-ethylene and the effect of hydrogen on the adsorbed species for palladium—silica at 20°C [53].

Fig. 27. 14C-acetylene adsorption isotherm on palladium—silica at 20°C (O) and the 14C-ethylene adsorption isotherm on an acetylene-precovered palladium—silica catalyst... 

Comparison of Palladium, Silica-CVD denied, and Zeolite Manbranes... 

Palladium-silica catalysts prepared from tetra-ammine palladous nitrate (to avoid chlorine introduction) showed a marked reduction effect , viz, the specific activity for benzene hydrogenation decreased with increased reduction temperature, i.e., 573 or 723Various explanations were considered, including a metal-support interaction. After reduction at 873 K, X-ray diffraction provided clear evidence of chemical reaction and at lower temperatures silicon insertion into palladium might still occur, which could either disrupt the palladium ensembles required for benzene adsorption or modify the properties of single palladium atoms, if these are the active sites. 

An examination of the ethylene-deuterium reaction at the surface of a palladium thimble has been briefly reported 54) the gas diffusing through the thimble during the reaction was found to contain 10% H. Final ethane distributions from this reaction over palladium-silica and palladium-charcoal under high pressure at —78° have been reported 46). 

Sault A.G., Martino A., Kawola J.S., Boespflug E. Novel sol-gel-based Pt nanocluster catalysts for propane dehydrogenation. J. Catal. 2000 191 474 79 Schubert U., Amberg-Schwab S., Breitscheidel B. Metal complexes in inorganic matrixes 4 Small metal particles in palladium-silica composites by sol-gel processing of metal complexes. Chem. Mater. 1989a 1 576-578... 

Silyl enol ethers are other ketone or aldehyde enolate equivalents and react with allyl carbonate to give allyl ketones or aldehydes 13,300. The transme-tallation of the 7r-allylpalladium methoxide, formed from allyl alkyl carbonate, with the silyl enol ether 464 forms the palladium enolate 465, which undergoes reductive elimination to afford the allyl ketone or aldehyde 466. For this reaction, neither fluoride anion nor a Lewis acid is necessary for the activation of silyl enol ethers. The reaction also proceed.s with metallic Pd supported on silica by a special method[301j. The ketene silyl acetal 467 derived from esters or lactones also reacts with allyl carbonates, affording allylated esters or lactones by using dppe as a ligand[302]... 

Benzyloxy-6-bromo-4-nitro-JV-(2-propeny])aniline (5.82 g, 16 mmol), tetra-ii-butylammonium bromide (5.16 g, 16 mmol) and titjN (4.05 g, 40 mmol) were dissolved in DMF (15 ml). Palladium acetate (72 mg, 2 mol%) was added and the reaction mixture was stirred for 24 h. The reaction mixture was diluted with EtOAc, filtered through Cclite, washed with water, 5"/o HCl and brine, dried and evaporated in vacuo. The residue was dissolved in CHjClj and filtered through silica to remove colloidal palladium. Evaporation of the eluate gave the product (4.32 g) in 96% yield. 

The "acyl effect" proves crucial in the formation of the perhydroazulene systems cyclization can only take place with the presence of an acyl group on the TMM portion whereas the parent hydrocarbon fails. For example, treatment of substrate (51) with the palladium catalyst gave a mixture of the bicyclic compounds (52) and (53) in 51% yield. The formation of endocyclic olefin (52) is presumed to occur when the first formed (53) was exposed to silica gel during purification [22]. This intramolecular cycloaddition strategy was utilized in a highly diastereoselec-tive preparation of a key intermediate (54) in the total synthesis of (-)-isoclavuker-in A (55) (Scheme 2.16) [21]. 

A mixture of 2.0 g (0.064 mol) of 2-fluoromethyl-3-(o-tolyl)-6-nitro-4(3H)-qulnazolinone, Oi g of 5% palladium-carbon and 100 ml of acetic acid is shaken for 30 minutes in hydrogen gas. The initial pressure of hydrogen gas is adjusted to 46 lb and the mixture is heated with an infrared lamp during the reaction. After 30 minutes of this reaction, the pressure of hydrogen gas decreases to 6 lb. After the mixture is cooled, the mixture is filtered to remove the catalyst. The filtrate is evaporated to remove acetic acid, and the residue is dissolved in chloroform. The chloroform solution is washed with 5% aqueous sodium hydroxide and water, successively. Then, the solution is dried and evaporated to remove solvent. The oily residue thus obtained is dissolved in 2 ml of chloroform, and the chloroform solution is passed through a column of 200 g of silica gel. The silica gel column is eluted with ethyl acetate-benzene (1 1). Then, the eluate is evaporated to remove solvent. The crude crystal obtained is washed with isopropylether and recrystallized from isopropanol. 0.95 g of 2-fluoromethyl-3-(o-tolyl)-6-amino-4(3H)-quinazolinone Is obtained. Yield 52.5% MP 195°-196°C. 

A solution of 1.5 mol equiv of butyllithium in hexane is added to 1.5 mol equiv of a 1 M solution of hexabutylditin in THF at 0 C under nitrogen, and the mixture is stirred for 20 min. The solution is cooled to — 78 °C and a solution of 1.5 mol equiv of diethylaluminum chloride in toluene is added. After stirring for 1 h at — 78 °C, a solution of 0.05 mol equiv of [tetrakis(triphenyl)phosphine]palladium(0) in THF is added followed by a solution of the allyl acetate in THF. The mixture is warmed to r.t., and stirred until the allyl acetate has reacted (TLC). The solution is cooled to 0°C, and an excess of aq ammonia slowly added. After an aqueous workup, the products arc isolated and purified by flash chromatography on silica gel using 1 % triethylamine in the solvent to avoid acid-induced loss of stannane. 

A silica-supported palladium reagent has been used to convert iodobenzene to butyl benzoate, in the presence of CO and butanol. Diaryl ketones can also be... 

In 2003, Sigman et al. reported the use of a chiral carbene ligand in conjunction with the chiral base (-)-sparteine in the palladium(II) catalyzed oxidative kinetic resolution of secondary alcohols [26]. The dimeric palladium complexes 51a-b used in this reaction were obtained in two steps from N,N -diaryl chiral imidazolinium salts derived from (S, S) or (R,R) diphenylethane diamine (Scheme 28). The carbenes were generated by deprotonation of the salts with t-BuOK in THF and reacted in situ with dimeric palladium al-lyl chloride. The intermediate NHC - Pd(allyl)Cl complexes 52 are air-stable and were isolated in 92-95% yield after silica gel chromatography. Two diaster corners in a ratio of approximately 2 1 are present in solution (CDCI3). 

The separation factors are relatively low and consequently the MR is not able to approach full conversion. With a molecular sieve silica (MSS) or a supported palladium film membrane, an (almost) absolute separation can be obtained (Table 10.1). The MSS membranes however, suffer from a flux/selectivity trade-off meaning that a high separation factor is combined with a relative low flux. Pd membranes do not suffer from this trade-off and can combine an absolute separation factor with very high fluxes. A favorable aspect for zeoHte membranes is their thermal and chemical stability. Pd membranes can become unstable due to impurities like CO, H2S, and carbonaceous deposits, and for the MSS membrane, hydrothermal stability is a major concern [62]. But the performance of the currently used zeolite membranes is insufficient to compete with other inorganic membranes, as was also concluded by Caro et al. [63] for the use of zeolite membranes for hydrogen purification. 

The auto-thermal reaction of ethanol occurred in the shell side of a palladium membrane reactor in which a Zn-Cu/AlaOs industrial catalyst (MDC-3) was packed with silica powder. Ethanol-water mixture (nH2o/nEioH=l or 3) and oxygen (noa/nEioH=0.2,0.776 or 1.035) are fed concurrently to the shell side. The reaction temperatures were set at 593-723 K and the pijrasures were 3 10 atm. 

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