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Версия для печати | Главная > Центр > Научные советы > Научный совет по катализу > ... > 2005 год > № 36

№ 36

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СОДЕРЖАНИЕ

Конференция РФФИ
"Фундаментальная наука в интересах развития критических технологий"
Владимир, 12-14 сентября, 2005 г.

О совещании Российских производителей катализаторов,
Владимир, 13 сентября 2005 г.

XVII симпозиум
"Современная химическая физика"
Туапсе, 18-25 сентября, 2005 г.

2-я Российская конференция
"Актуальные проблемы нефтехимии",
Уфа, 11-13 октября 2005 г.

За рубежом




Конференция РФФИ

Переход к элементу

Свернуть/Развернуть


О совещании российских производителей катализаторов

Переход к элементу

Свернуть/Развернуть


XVII симпозиум "Современная химическая физика"

Переход к элементу

Свернуть/Развернуть


2-я Российская конференция "Актуальные проблемы нефтехимии "

Переход к элементу

Свернуть/Развернуть


За рубежом

Переход к разделу

Any shape you want, you get
Rods, cubes, stars, and hexagons: These are just a few of the shapes into which gold nanoparticles can be coaxed into forming uniformly and in high yield. University of South Carolina, Columbia, chemists Tapan K. Sau and Catherine J. Murphy control nanoparticle shape by systematically varying the parameters of a solution-based seed-mediated procedure they developed for producing nanocrystals. The procedure involves preparing gold seed particles and then adding an amount of the seed solution to a solution containing cetyltrimethylammonium bromide, chloroauric acid (HAuCl4), ascorbic acid, and sometimes a small amount of silver nitrate [J. Am. Chem. Soc., 126, 8648 (2004)]. The procedure is note-worthy not only for its high yield but also for its simplicity, requiring only aqueous solutions, room temperature, and one surfactant instead of various additives to control particle size and shape.

HTTP://WWW.CEN-ONLINE.ORG
Ñ & EN / JULY 12, 2004

Binary catalyst aids synthesis of polycarbonates
One of the most promising green polymerization processes is the alternating copolymerization of CO2 and epoxides to make polycarbonates. Several research groups have been exploring ongoing problems in polycarbonate synthesis related to catalyst efficiency, reaction conditions, and control of polymer structure and molecular-weight distribution. In the latest effort, Xiao-Bing Lu and Yi Wang at Dalian University of Technology, in China, report a novel binary catalyst system that affords an efficient conversion of CO2 and propylene oxide to poly-(propylene carbonate) with high selectivity and stereoregular control under mild reaction conditions [Angew. Chem. Int. Ed., 43, 3574 (2004)]. The researchers used a chiral cobalt-(III) salen complex in conjunction with a quaternary ammonium salt, optimizing the catalyst activity by changing a substituent group on the cobalt catalyst and changing the quaternary ammonium anion. They achieved two- to threetimes higher catalyst turnover frequency at significantly lower CO2 pressure than previously reported by others using a cobalt catalyst alone.

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Ñ & EN / JULY 12, 2004

Simpler strategy for direct C-C coupling

strustureA new type of selective C-C bond-forming reaction has been devised in which C-H bonds of two molecules cross-couple together in the simplest way possible to construct complex organic molecules of pharmañeutical interest. The"crossdehydrogenative coupling (CDC) reaction, developed by Zhiping Li and Chao-Jun Li of McGill University, in Montreal, eliminates the need to first functionalize molecules before they can be coupled together and avoids the need for secondary elimination or hydrogenation reactions. Overall, the strategy makes synthetic schemes shorter and more efficient, the researchers note. They recently reported CDC reactions between sp3 and sp carbon atoms and between sp3 and sp3 carbon atoms, and now report examples of sp3-sp2 coupling (J. Am. Chem. Soc. 2005, 127, 6968). In the indolyl tetrahydroisoquinoline derivative shown, the red bond comes from a CDC reaction between the sp3 C-H bond of a quinoline and an aryl sp2 C-H bond of an indole. CDC reactions are carried out under mild conditions and are catalyzed by relatively inexpensive copper bromide.

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Ñ & EN / MAY 23, 2005

Oxaziridines catalyze C-H oxidation selectively

strustureThe oxaziridines shown catalyze the regioselective hydroxylation of unactivated C-H bonds, according to a new study (J. Am. Chem. Soc. 2005, 127, 15391). Alkane hydroxylation remains a formidable challenge in reaction design, write Justin Du Bois and Benjamin H. Brodsky of Stanford University. Certain oxaziridines are known to convert alkanes to alcohols stoichiometrically. Brodsky and Du Bois now report novel N-alkoxysulfonyl oxaziridines that can be used to perform such hydroxylations catalytically. The oxaziridines were generated in situ by treating the corresponding imine precursors with hydrogen peroxide and a suitable cocatalyst. The researchers find that the oxaziridine system performs regioselective and stereospecific oxidations of a variety of aliphatic substrates, including alkenes and alcohols. Guided by computational modeling, they are now refining the catalyst to improve turnover rate and substrate scope.

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Ñ & EN / OCTOBER 31, 2005

Chemical steps to biomass fuel

Integrated biorefineries have been proposed as a way to make gasoline, diesel fuel, and chemical feedstocks directly from carbohydrates such as sugars, starch, and cellulose derived from dedicated crops, agricultural waste, and urban yard debris. Chemical engineers George W. Huber, James A. Dumesic, and coworkers at the University of Wisconsin, Madison, who have been developing lab-scale chemical processes that could be important in biorefineries, now report chemistry to produce C7 to C15 alkanes from biomass (Science 2005, 308,1446). The team designed a multistep aqueous-phase process that begins with carbonyl-containing intermediates, such as hydroxymethylfurfural, that can be made from glucose. The intermediates first undergo an aldol cross-condensation with acetone or an aldol self-condensation using a solid base catalyst to make larger compounds, followed by a dehydration-hydrogenation process that uses a bifunctional metal-acid catalyst to form the linear alkanes. The alkanes can be phase-separated from the water. Biorefinery production of alkanes to make sulfur-free gasoline and diesel could be more energy-efficient and less costly than producing ethanol or hydrogen from biomass.

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Ñ & EN / JUNE 6, 2005

Engelhard buys catalyst line

Engelhard has expanded its catalysts business with the acquisition of the synthesis gas catalyst unit of Nanjing Chemical Industry, a subsidiary of Sinopec. Though Engelhard won't say how much it paid for the business, a spokesman says the purchase includes manufactoring and R&D facilities in Nanjing that employ more than 600 people. Engelhard manufactures the cobalt catalyst for Sasol's Fischer-Tropsch slurry bed reactor, used to convert natural gas to synthetic diesel and petrochemical feedstock. The firm says the Nanjing Chemical business will extend its gas-to-liquids catalyst operation into the market for syngas used to make ammonia, hydrogen, methanol, and other products.

HTTP://WWW.CEN-ONLINE.ORG
Ñ & EN / JUNE 6, 2005

Nanocluster catalyst lives longer

Chinese chemists report a rhodium nanocluster catalyst that demonstrates "unprecedented " lifetime and activity in benzene hydrogenation under forcing conditions (J. Am. Chem. Soc. 2005, 127, 9694). The rhodium nanoclusters, which tend to coalesce into bulk metal on their own, are stabilized by the novel combination of a pyrrolidone-substituted, ionic-liquidlike copolymer dissolved in an imidazolium ionic liquid. The total turnovers for the catalyst - a measure of catalytic lifetime - exceeded 20,000 over five runs, which is more than five times the previous record for benzene hydrogenation by a nanocluster catalyst. Yuan Kou and coworkers at Peking University suggest that the high stability and activity of the rhodium catalyst are due to the combined stabilizing influences of the ionic liquid and the pyrrolidone-substituted copolymer. The stabilized rhodium nanoclusters, each roughly 3 nm across, were synthesized by hydrogenation of a mixture of RhCl3. 3H2O and the copolymer dissolved in the ionic liquid.

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Ñ & EN / JUNE 27, 2005

Catalyst caught on a tape

Chemist regard tape made of DuPont's Teflon as an indispensable sealer for lab equipment, but according to researchers in Germany, Teflon tape may be just as useful inside a reaction flack. John A. Gladysz and Long V. Dinh of the University of Erlangen-Nuremberg have discovered that Teflon tape is surprisingly effective at introducing and recovering homogeneous fluorous catalysts from a reaction mixture (Angew. Chem. Int. Ed. 2005, 44, 4095). Thermomorphic fluorous catalysts dissolve in organic solvents only at elevated temperatures, so chemists usually have to heat their reaction mixtures to get the catalyst into solution and then cool and decant the mixture to recover the catalyst. Gladysz and Dinh found that if they added Teflon tape to a ketone hydrosilylation reaction featuring a fluorous rhodium catalyst, the reaction could proceed with much less catalyst. Upon cooling, the catalyst clung to the tape so that the chemists could fish it out of the mixture. The researchers speculate that their findings could lead to industrial-scale reactors or reactor components that use Teflon to release and recapture certain fluorous catalysts.

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Ñ & EN / JUNE 27, 2005

Enzyme mimic raises questions

strusture A model complex that mimics the active site of tyrosinase hydroxylates phenol substrates by a mechanism different from the one the enzyme is thought to use, according to a new study (Science 2005, 308, 1980). Liviu M. Mirica, Daniel Stack, and coworkers at Stanford University say their findings raise the possibility that tyrosinase may use an alternative mechanism, too. Tyrosinase - which plays a key role in melanin formation - relies on a pair of copper ions to activate O2, which then hydroxylates a CH group of a phenol. The CuO2Cu active species has long been assumed to contain an intact O2 molecule, with each oxygen atom bound to both Cu(II) ions. In the model complex, however, hydroxylation is performed by a bis(oxo)dicopper(III) species (Shown, R=tert-butyl) formed then the substrate binds. The O-O bond has already been broken in this species, which has detected spectroscopically at -120 oC and confirmed computationally. It remains to be seen whether tyrosinase uses such a species, Stack notes.

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Ñ & EN / JUNE 27, 2005



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