Search

A rhodium-based system in which the formation of the dipolarophile/catalyst complex is favored with respect to nitrone coordination is presented. It represents a rare example of efficient activation of electron-deficient monofunctionalized alkenes towards the 1,3-dipolar cycloaddition reaction of nitrones.

Me2NH.BH3 acts as a reducing agent to generate catalytically active Rh colloids and a stoichiometric hydrogen source for the hydrogenation of alkenes in a one-pot procedure at 25 degree C is demonstrated.

The direct catalytic asymmetric mannich reaction is mediated by small organometallic and organic amine catalysts, which can achieve levels of selectivity similar to those of natural enzymes. The recent developments and contributions regarding this research is presented.

Byline: Sheila W. Hedges, Henry W. Pennline The selective catalytic reduction of nitric oxide with hydrocarbons in an oxygen-containing simulated flue gas has been investigated for a series of copper oxide and cerium oxide alumina supported catalysts at 600775 K. The activity of these catalysts for the reduction of NO by methane or propane has been investigated in simulated flue gas. The effects of sulphates on the catalyst, and of water vapour and/or gaseous sulphur dioxide have been examined for both the SCR of NOx by propane and direct decomposition of NO. Both copper sulphate on alumina and cerium sulphate on alumina are substantially less active for propane SCR than the respective oxides. Both catalyst types are reversibly inhibited by the presence of water vapour. The effect of sulphur dioxide in the gas stream appears to be only mildly inhibiting, but since the optimum temperature range for propane reduction of NO is the same as the optimum temperature range for SO2 absorption, the CuO/Al2O3 sorbent/catalyst will quickly become sulphated, even at low flue gas SO2 concentrations. Methane was also examined as a reductant, and neither copper oxide/alumina nor cerium oxide/alumina is active for selective catalytic reduction of NOx with methane up to 775 K.

Research has been conducted on olefinic iodoethers. Results demonstrate that the catalytic reductive cyclization of these compounds has been achieved via the use of Cp (sub)2 TiCl (sub)2 in the presence of Me (sub)3 SiCl and Mn.

Research has been conducted on primary alcohols. The results of the Oppenauer oxidation of these compounds with 2-butanone or acetone carried out via the use of amino alcohol-based iridium bifunctional catalyst are described.

A highly efficient route to N-tert-buttoxycarbonyl-(N-Boc) protected beta-amino acids through the enentioselective addition of silyl ketene acetals to N-Boc-aldimines catalyzed by thiourea catalyst is presented. The conclusion states that urea derivatives of general structure serve as highly effective catalysts for the asymmetric addition of silyl ketene acetal derivatives to aldimines.

The study deals with an approach to synthesize highly functionalized ROM polymers utilizing grubbs ruthenium catalyst C1(sub 2)(Cy3(sub 2))Ru=CHPh to perform ring-opening metathesis, thus generating living polymers. They have shown that ROM polymers including ROMPgels are very useful support for the immobilization of reagents and scavengers.

Oligonucleotides containing the guanine nucleobase were adsorbed onto fro electrodes from mixtures of DMF and acetate buffer. Chronocoulometry and chronoamperometry were performed on the modified electrodes in both phosphate buffer and buffer containing low concentrations of the inorganic complex [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (bpy = 2,2' bipyridine), which catalyzes guanine oxidation. The charge and current evolution with and without the catalyst were compared to the charge and current evolution for electrodes that were treated with identical oligonucleotides that were substituted at every guanine with the electrochemically inert nucleobase hypoxanthine. Chronocoulometry over 2.5 s shows that roughly 2 electrons per guanine were transferred to the electrode in both the presence and absence of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], although at a slower rate for the uncatalyzed process. Chronoamperograms measured over 250 ms can be fit to a double exponential decay, with the intensity of the fast component roughly 6-20 times greater than that of the slow component. First- and second-order rate constants for catalytic and direct guanine oxidation were determined from the fast component. The maximum catalytic enhancement for immobilized guanine was found to be [i.sub.cat]/[i.sub.d] = 4 at 25 [micro]M [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. The second-order rate constant for the catalyzed reaction was 1.3 x [10.sup.7] [M.sup.-1] [s.sup.-1], with an apparent dissociation constant of 8.8 [micro]M. When compared to parallel studies in solution, a smaller value of the dissociation constant and a larger value of the second-order rate constant are observed, probably due to distortion of the immobilized DNA, an increase in the local negative charge due to the oxygen sites on the ITO surface, and redox cycling of the catalyst, which maintains the surface concentration of the active form.

Reduction of cold-start emissions using electrically-heated catalyst (EHC) technology was the focus of this work. Comprehensive emission measurements of CO, [CO.sub.2], [NO.sub.x], and total hydrocarbons (THC) are reported for a spark-ignited engine operated on baseline gasoline and compressed natural gas (CNG). Electric heating times of 0, 20, and 40 s with and without secondary air injection were investigated. The 40-second electric catalyst heating with secondary air injection scenario yielded the greatest catalyst system (EHC+OEM three-way catalyst) conversion efficiencies for THC, CO, and [NO.sub.x] for gasoline and natural gas fueling. Electric catalyst heating coupled with secondary air injection significantly improved THC and CO emissions for gasoline fueling. THC oxidation was difficult for CNG fueling due to the high content of nonreactive methane in the fuel. The independence of [NO.sub.x] emissions on heating time was demonstrated for all fueling cases. [DOI: 10.1115/1.1340640]

An efficient and affordable catalyst could improve access to clean drinking water in remote areas. Hydrogen peroxide is commonly used to treat water and as a disinfectant, but it is [...]

3-aminomethyl-2-azabicyclo(2,2.1)heptanes (4a-b) have been prepared and their Li-amides used as catalysts for the rearrangement of meso-epoxides into chiral allylic alcohols. The route is efficient for both enantiomers and diamines, and the Li-amides were found to be highly efficient. The catalytic performance can be improved by DBU, through the prevention of less selective Li-amide aggregates forming.

Organolanthanide and group 3 organometallic complexes have uses as catalysts in organic synthesis. The ability to predict the chemoselectivity of the reaction prior to preparation of the starting material is of major concern. Substituion patterns will depend wholly on catalyst reactivity, and it has been demonstrated that reactivity relies on the steric environment of the alkene or alkyne. Using the catalysts Cp(sub2)YMe.THF and (CpTMS(sub2)YMe)(sub2), alkynes and alkenes exhibited increased reaction rate due to electronic effects.

In times of depleting crude oil sources and increased environmental concern over greenhouse gas emissions, researchers are increasingly investigating alternative propulsion systems to power modern vehicles. Currently, one of the [...]

The use of a bifunctional catalyst is reported for the anti-markovnikov hydration of terminal alkynes to aldehydes. The catalyst also exhibits enzyme-like rate acceleration and selectivity.

The reaction rate was determined in the alpha-aminoxylation of aldehydes via in situ monitoring of the reaction progress as function of time. The results of kinetic investigations reveals that like the aminoxylation, this reaction of the alpha-amination of aldehydes exhibits autoinductive rate behavior and amplification of product.

The use of an aptamer-functionalized Au nanoparticles as catalytic label for the amplified detection of thrombin in solution and surfaces is reported. Biomaterial-metallic nanoparticles hybrid systems are extensively used in different bioanalytical applications.

The studies done on developing catalytic, diastereoselective synthesis of beta-hydroxy esters from alpha, beta-epoxy aldehydes and its application to a unique esterification process are discussed. A new catalytic method is developed for the preparation of these important structural motifs from readily available starting materials.

The electrophilic Ir(III) complex having a labile DIB chelate is a very reactive catalyst for promoting the Nazarov cyclization of aryl and divinyl ketones. This is the first example of catalysis of the Nazarov cyclization using a well-defined cationic metal complex having two adjacent substrate sites.

The dependence of catalytic activity on the pore size of mesoporous silica (M-41) samples is investigated. Results indicate that catalytic activity was strongly dependent on the pore diameter of the catalyst and was maximized at about 1.9 nm.

The reaction of C60 with 1 equiv of barbituric acid under modified Bingel conditions (CBr4, DBU) resulted in the formation of a complex mixture of products. The photoinduced dimerization or polymerization of fullerene is limited to the irradiation of solid samples and microheterogeneous suspensions.

A novel catalytic four-component strategy that allows the direct coupling of aryl iodides, aldehydes, acrylates, and dimethylzinc to produce conjugate addition/aldol products without requiring the formation of metalated aryl organometallic is presented. This method avoids the typical requirement of preparing sensitive, metalated, organometallic nuclophiles, and shows that dimethylzinc plays an important role in reaction acceleration.