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№ 39

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VII Российская конференция
Механизмы каталитических реакций"

II Международный симпозиум
"Углерод в катализе" "Карбокат-II"

Школа-конференция
молодых ученых-нефтехимиков

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VII Российская конференция "Механизмы каталитических реакций"

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II Международный симпозиум "УГЛЕРОД В КАТАЛИЗЕ"

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Школа-конференция молодых ученых-нефтяников

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Новости науки

Gentler fuel cleanup using zeolites

Nitrogen compounds in transportation fuels can be reduced to very low concentrations using zeolite-based adsorbents under ambient conditions, according to a study conducted at the University of Michigan, Ann Arbor. In oil refineries worldwide, nitrogen and sulfur contaminants are removed from feedstocks simultaneously using hydrotreating techniques that are carried out at temperatures above 300 °C and H2 pressures of up to 100 atm in the presence of CoMo and NiMo catalysts. Hydrotreating is more effective for removing organosulfur compounds than organonitrogen species, which tend to be relatively unreactive. But now, Michigan chemical engineers Arturo J. Hernandez-Maldonado and Ralph T. Yang have shown that Y-zeolite containing copper cations can remove nitrogen compounds efficiently at room temperature and pressure [Angew. Chem. Int. Ed., 43, 1004 (2004)]. Using conventional ion-exchange methods to prepare adsorbents, the team reduced the nitrogen concentration in commercial diesel fuel samples from 83 ppm by weight to well below 0.1 ppm by weight. The researchers point out that the material's adsorption capacity is readily regenerated using solvents or heat treatments.

HTTP://WWW.CEN-ONLINE.ORG
Ñ & EN / FEBRUARY 16, 2004

Slow growth key to Pt nanowires

Large quantities of uniform, single-crystal platinum nanowires can be grown using a solution-based process developed by chemists at the University of Washington, Seattle. Platinum nanostructures interest chemists chiefly because of their potential as catalysts, but to grow anisotropic structures, like nanorods or nanotubes, scientists usually employ a template to guide the structure's growth, Younan Xia and colleagues discovered that by using iron salts to slowdown the reaction rate during a polyol reduction of H2PtCl6 or K2PtClg, they can grow platinum nanowires in solution without any templating [J. Am. Chem. Soc, published online Aug. 17, [http://dx.doi.org/10.1021/ja0468224;http://dx.doi.org/10.1021/ja0468224]. During the first few hours of the process, Xia's group notes that the Pt atoms form nanoparticle agglomerates. As the reaction rate slows, the Pt atoms organize into nanowires on the agglomerates' surfaces. The final structures look like sea urchins. Xia's group then strips the nanowires away from the agglomerates using a simple combination of sonication and centrifugation.

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Ñ & EN /AUGUST 5, 2004

Photochemical dechlorination

A new catalytic system for dechlorinating chlorinated organic pollutants employs a vitamin B-12 derivative and a ruthenium photosensitizer Yoshio Hisaeda and coworkers at Kyushu University, Fukuoka, Japan, used the system to catalyze the dechlorination of DDT[l,l,l-trichloro-2,2-bis(p-chlorophenyl)ethane] under visible light irradiation [Chem. Commun., published online July 28, http://dx.doi.org/10.1039/b406400c]. The catalyst, hydrophobic vitamin B-12, has ester groups in place of the peripheral amide moieties of naturally occurring vitamin B-12. The system exhibits high catalytic efficiency and stability during the dechlorination.
The authors postulate that the hydrophobic vitamin B-12, which contains cobalt (H), is reduced to a supernucleophilic Co(I) species by the ruthenium photosensitizer. The Co-C bond of the alkylated complex generated by the reaction of the supernucleophile with DDT is cleaved by photolysis to form a substrate radical and a Co(II) species. The radical reacts with H2 to form, as the main product, a DDT derivative having a CHC12 group instead of CCl3. The system is simpler and more facile than conventional electrochemical dehalogenation systems, the authors say.

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Ñ & EN / AUGUST 16, 2004

Warfarin chiral switch in one efficient catalytic step

atom-economical synthesisAn atom-economical synthesis of single enantiomers of the anticoagulant warfarin has been achieved with organic catalysts. The route was developed by chemists Nis Halland, Tore Hansen, and Karl Anker Jorgensen at Aarhus University, in Denmark [Angew. Chem. Int. Ed., 42, 4955 (2003)]. The work lays the ground for a facile chiral switch for the widely used anticoagulant. The S enantiomer is more active than the R enantiomer. And because of the difference in the metabolism of the enantiomers, dosing with the racemic drug can be problematic. The Danish group prepares single-enantiomer warfarin by mixing at room temperature 4-hydroxycoumarin and benzylideneacetone in dichloromethane in the presence of an imidazolidine catalyst
(10 mol %). Yields of up to 96% are achieved, with enantiomeric excesses of up to 82%, which may be raised to greater than 99.9% by a recrystallization in acetone/water.

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Ñ & EN / OCTOBER 20, 2003

Organometaluc catalysts are enzyme-like

structureResearchers have discovered organometallic catalysts that work about as well as enzymes in anti-Markovnikov hydrations of terminal alkynes to aldehydes. In such hydrations, a carbonyl oxygen is added to the alkyne's terminal carbon, producing an aldehyde, whereas Markovnikov hydrations yield ketones. Alkyne hydrations are generally carried out with strongly acidic or metal-containing catalysts under acidic conditions, but such reactions generally proceed in a Markovnikov manner and produce mostly ketones. Douglas B. Grotjahn and Daniel A. Lev of San Diego State University have now identified organo-metallic compounds (shown, where X is an anion like PF6-) that catalyze anti-Markovnikov alkyne hydrations with extraordinary speed and selectivity {J. Am. Chem. Soc, 126, 12232 (2004)}. The catalysts accelerate aldehyde formation at rates 10 to 11 orders of magnitude faster than those of corresponding uncatalyzed reactions, and they are selective for production of aldehydes over ketones by factors of 10,000-to-1 or more.

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Ñ & EN / OCTOBER 4, 2004

Soluble polymer support aids catalysis

structure Poly(4-tert-butylstyrene) copolymers are effective soluble catalyst supports for homogeneous reactions in mixed solvent systems where the products can be recovered by "latent" biphasic separations [Org. Lett., 5, 2445 (2003)]. Chemistry professor David E. Bergbreiter and graduate student Chunmei Li at Texas A&M University synthesize polymers containing a triarylphosphine or dimethyl-aminopyridine catalyst side chain (shown). In one sample reaction, the polymer-catalyst conjugate dissolved in heptane was combined with 2-nitro-propane and methyl acrylate reactants in ethanol at room temperature. The heptane-aqueous ethanol mixture was formulated to just remain miscible during the reaction. But when the reaction was finished, phase separation was prompted by adding a little water. The polymer-catalyst went into the nonpolar heptane and was recycled, while the addition product went into the polar ethanol for recovery. Formulating polymer-catalyst combinations that are soluble in either polar or nonpolar solvents to match the expected solubility of the product should be possible, the researchers conclude.

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Ñ & EN / JULY 14, 2003

Sugary catalyst for biodiesel

A new solid acid catalyst for making the increasingly popular fuel biodiesel trumps other catalysts, report Masakazu Toda at Tokyo Institute of Technology in Yokohama and colleagues. Made from sulfonated burnt sugar, the catalyst is inexpensive and recyclable and keeps working at temperatures up to 180 °C (Nature 2005,438, 178). Unlike sulfuric acid, the commonly used catalyst, the new catalyst is environmentally friendly; and because it's solid, it doesn't require separation. It's also up to eight times more active than other solid acid catalysts, such as the expensive Nafion, made by DuPont. The japanese group first partially carbonizes sugar, starch, or cellulose. The reaction generates polycyclic aromatic carbon sheets, which are then sulfonated with sulfuric acid to produce sheets of amorphous carbon impregnated with hydroxyl, carboxyl, and sulfonite (SO3H) groups. The resulting black powder can be made into hard pellets or thin films. That is a useful property for large-scale biodiesel production, notes James G. Goodwin, chair of the chemical and bio-molecular engineering department at Clemson University, in South Carolina.

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Ñ & EN / NOVEMBER 14, 2005


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