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Версия для печати | Главная > Центр > Научные советы > Научный совет по катализу > ... > 2017 год >  № 81

№ 81

 

Содержание

  • Роман Алексеевич Буянов. К 90-летнему юбилею
  • НАУЧНЫЙ СОВЕТ ПО КАТАЛИЗУ ОХНМ РАН
    Отчет о научно-организационной деятельности в 2016 году
  • Международная конференция ХИМРЕАКТОР-22
  • За рубежом
  • Приглашения на конференции


Роман Алексеевич Буянов. К 90-летнему юбилею

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НАУЧНЫЙ СОВЕТ ПО КАТАЛИЗУ ОХНМ РАН
Отчет о научно-организационной деятельности в 2016 году

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Международная конференция
ХИМРЕАКТОР-22

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Database of hazardous reactions launched

Tool allows scientists to submit and search for safety information not publicly cataloged elsewhere

A nonprofit group today released a database tool chemists can use to share information about hazardous chemical reactions. Called the Chemical Safety Library, the tool was developed by a group that included representatives from pharmaceutical companies and academic institutions.

“We feel this will be a valuable and unique set of data that is currently not available and should advance safety for all researchers,” says Carmen Nitsche, executive director for business development in North America at the Pistoia Alliance, which brings together companies, vendors, publishers, and academic groups to address research and development challenges in the life sciences industry.

The project started when chemists at Bristol-Myers Squibb were looking for a better way to catalog and share information about lab accidents and other adverse events. Eventually the project landed at Pistoia.

“I didn’t know if we were going to get any interest” in putting together the library, says Mark Manfredi, a business capability manager at Bristol-Myers Squibb. “But right from the first meeting, we had several organizations that were interested in participating.”

To use the Chemical Safety Library, chemists must first register for an account. They can then start entering reaction information, including specific reagents as well as reaction class, hazard category, scale, warning message, and additional information such as a literature reference. Pistoia worked with Millipore Sigma and Biovia to preload more than 75,000 reagents to help ensure accuracy. Library administrators review submitted reaction entries to ensure they are appropriate.

Chemists may search the library for particular reactions or reagents or even download the full data set. An organization could incorporate downloaded data into an electronic laboratory notebook system to issue an alert when a particular combination of reagents associated with a known hazard is entered. Bristol-Myers Squibb is already using the data in an electronic laboratory notebook system and an ordering system, Manfredi says.

Pistoia sees the current library tool as an experiment to gather information about the willingness of the community to populate and use the database, Nitsche says. Pistoia will analyze database use to determine the resources and technology needed to sustain the library long-term.

The library will be a “wonderful resource” for researchers to use as an additional source of information when doing hazard and risk assessments of experiments, comments Bettyann Howson, chair of the American Chemical Society’s Committee on Chemical Safety. ACS also publishes C&EN. C&EN plans to encourage scientists who submit safety letters to also enter the information into the Chemical Safety Library.

 

Custom designed zeolites make better catalysts

Zeolites synthesized with transition state mimics exhibit enhanced activity and product selectivity

To make an active zeolite catalyst with pores that match the structure of a given reaction transition state (right), researchers used a transition state mimic (left) as a structure-directing agent to synthesize the zeolite.

Endowed with a network of interconnected, molecule-sized pores and channels, zeolites have been used in chemical separations, oil refining, and catalysis for decades. Yet scientists still tend to use a trial-and-error approach to find the best member of this large family of crystalline materials for a given application.

Researchers in Spain may have come up with a way to shorten and reduce the cost of that time-consuming search process. Their strategy is to tailor-make zeolite catalysts with pores that closely match the proposed transition state structure of a given reaction. They find that the customized zeolite outperforms commercial zeolite catalysts commonly used for that reaction (Science 2017, DOI: 10.1126/science.aal0121).

In one example of this approach, the team, which was led by Avelino Corma, the director of the Institute of Chemical Technology at Polytechnic University of Valencia, produced catalysts for the production of xylene from toluene. That reaction, which is carried out commercially mainly with ZSM-5 and mordenite zeolites, converts two toluene molecules to one molecule of benzene and one of the dimethylbenzene isomers (o-, m-, or p-xylene).

Based on earlier studies, researchers have proposed that the reaction proceeds by way of a transition state featuring a complex made of two phenyl rings joined by a positively charged carbon atom. A zeolite catalyst would need pores big enough to accommodate that structure, which is larger than the reactants and the products.

So the Valencia team selected a diphenylphosphonium compound that closely mimics the structure and charge of the transition state and used it as a structure directing agent (SDA) to synthesize a zeolite. All zeolites are aluminosilicate minerals. The team produced their zeolite catalyst, called ITQ-27, by allowing the mineral to crystallize around the diphenylphosphonium molecules. They then heated the zeolite to remove the organic material, leaving an aluminosilicate frame with pores matching the SDA and the transition state structure.

Then the team compared the performance of ITQ-27 with that of ZSM-5, mordenite, and other zeolites. They found that although some of the zeolites had a larger number of catalytic sites than ITQ-27, the custom-made ITQ-27 was the most active catalyst. It was also as selective or more selective, meaning it produced fewer by-products, than the other catalysts.

In another example of the transition state strategy, Corma and coworkers successfully synthesized zeolites for ethylbenzene isomerization.

This approach, which represents “a new paradigm in zeolite science, may accelerate discovery of highly active and selective zeolite catalysts,” says Roberto Millini, a specialist in materials chemistry and catalysis at Eni, an oil and gas company based in Italy.

Millini notes that in addition to improving the efficiency of petrochemical processes, this strategy may enable new applications for crystalline porous materials. For example, these materials may provide environmentally benign routes for converting biomass to biofuels and chemicals.

 

Enzyme-inspired route to heterocycle functionalization

Bifunctional metal agents reversibly coordinate heterocycles and derivatize them at remote sites

A bimetallic reagent’s anchoring palladium (near center) coordinates with the nitrogen atom of a substrate (quinoline in this case), positioning the reagent’s second palladium (lower right) to activate a remote C–H bond.

Chemists often use C–H activation to help replace specific hydrogen atoms in organic compounds with complex functional groups. This strategy generally involves covalently bonding a reagent containing a C–H-activating group, such as a palladium atom, to a substrate that already has a directing functional group. The directing group steers the C–H activator to the desired C–H bond. Once the bond breaks, a new functional group replaces hydrogen and the directing group is removed.

A new class of bimetallic reagents now uses enzyme-inspired reversible metal coordination, instead of covalent bonding, to achieve C–H activation and functionalization in nitrogen heterocycles, with no need to preinstall or later remove a directing group. The reagents, designed by Jin-Quan Yu and coworkers at Scripps Research Institute California, also activate remote C–H bonds that have been difficult to reach or completely inaccessible with other synthetic techniques (Nature 2017, DOI: 10.1038/nature21418).

C–H activation hasn’t worked well with heterocycles because metal activators tend to coordinate with heteroatoms, interfering with site selectivity. Yu and coworkers have now turned that problem into an advantage. In their new bimetallic reagents, one palladium atom is designed intentionally to coordinate reversibly with the heteroatom of a substrate, positioning the second metal to activate a remote C–H bond.

The reagents use distance and geometry constraints to focus on specific target sites on substrates, like enzymes do. They coordinate reversibly with substrate molecules, derivatize them, detach after activation, and then move on to activate other substrate molecules, also like enzymes do. The reagents work stoichiometrically or catalytically, and relatively large amounts are required. But their efficiency can potentially be improved, experts say.

Yu and coworkers used the new reagents to alkenylate a range of nitrogen heterocycles, including phenylpyridine, quinoline, and the anticancer natural product camptothecin, none of which could previously be functionalized in the same way using C–H activation, Yu says.

Motomu Kanai of the University of ­Tokyo comments that the technique is “very powerful,” noting that it could ease drug design by making it possible to modify compounds at positions other methods cannot easily reach. Victor Snieckus of Queen’s University in Ontario calls the discovery “a major leap forward in synthetic aromatic substitution chemistry.” And Kian Tan, who leads the Chemical Technology-Synthesis group at Novartis in Cambridge, Mass., says the templates are amazingly well designed and versatile, making it “easy to envision creating libraries of templates to access different selectivity patterns.”

 

Fractious fractions teased from crude oil

Separation method corrals key compounds to improve petrochemical processing and pollution assessment

Crude oil is an unruly soup of tens of thousands of different organic compounds, and this diversity makes it difficult to pick out individual molecules from the crowd for analysis using standard tools like mass spectrometry. Despite the vast quantities of crude oil used globally each day, much remains unknown about its chemical composition, which can vary dramatically from one oil field to the next.

So a method that separates crude oil into a dozen fractions, based on their chemical properties, now promises to help measure levels of molecules that could trigger corrosion in a pipeline, or pinpoint the most toxic compounds in an oil spill (Anal. Chem. 2017, DOI: 10.1021/acs.analchem.6b04202).

Fractionation is not a new approach to simplifying oil analysis. One of the most common methods, dubbed SARA, uses chromatography to split the oil into four broad classes: saturates, aromatics, resins, and asphaltenes. But this separation is largely based on the molecules’ solubilities in the solvent being used, and many chemical classes remain obscured within the mélange in each fraction.

In contrast, the new method developed by Steven J. Rowland of the University of Plymouth and coworkers is particularly good at teasing apart polar compounds containing nitrogen, sulfur, or oxygen—often responsible for poisoning oil-processing catalysts—which conventional analytical methods struggle to identify.

The procedure is not based on radical innovation: It relies on a series of columns filled with commercial ion exchange resins and silica, making the method reproducible, relatively simple, and inexpensive. “The real novelty is putting it all together,” says Ryan P. Rodgers, director of the Future Fuels Institute at Florida State University, who was not involved with the work. By deploying the separation columns in the right order and eluting the crude with a series of increasingly polar solvents, the method isolates molecules depending on how well their functional groups stick to each type of column. This yields fractions that are each dominated by a particular chemical class: sulfoxides, quinolines, carbazoles, fluorenones, and more.

After analyzing each fraction with techniques such as gas chromatography-mass spectrometry (GC-MS), the team identified dozens of specific compounds. Some of them, such as thioxanthones, were previously unknown in crude oil. The method achieves “a better separation between different classes of chemicals,” says Sonnich Meier of the Institute of Marine Research. “It’s the best I’ve seen.”

Meier has been working with Rowland’s team for the past three years, and plans to use the technique to single out the compounds in crude oil that are toxic to fish embryos. Polyaromatic hydrocarbons account for about 60% of oil’s toxicity, says Meier, but the culprits responsible for the remainder of the effect are unknown. “There are thousands of compounds in oil that we just ignore, because we’re not good at analyzing them,” he says. These data will feed into a new risk assessment on the potential exploitation of oil reserves in the Lofoten region of northern Norway, currently a matter of fierce debate in the country.

Meanwhile, the oil industry increasingly wants to know the precise composition of a crude oil before investing billions in extracting and refining it. The world’s declining production of low-sulfur oil, known as sweet crude, means there is more reliance on crudes that contain higher proportions of heteroatoms and heavier compounds, requiring more refining and presenting new processing challenges, such as pipeline corrosion or blockages. The oil industry has expressed interest in the method, Rowland says.

 

Stable colloids made with inorganic molten salts

Potential applications include improved heat-transfer fluids and new inorganic thermoelectric materials

A new study proposes that chemical bonding of surface atoms (orange) of a nanocrystal to solvent ions (blue) of a molten inorganic salt is required for colloidal stability. Outer spheres are solvent ions.

A colloidal solution is a uniform dispersion of two completely different types of components—particles or droplets of one phase, called the solute, in a second, typically liquid, phase, called the solvent. Milk, a colloid of tiny globs of butterfat in water, is one of the most familiar.

Up to now, colloids have nearly exclusively been formed in polar solvents such as water or in organic solvents. Dispersions of silica particles in molten inorganic salts have been made before, but they have been metastable—that is, their colloidal form eventually breaks down.

Now, Dmitri V. Talapin of the University of Chicago and coworkers report the first stable colloids of nanoparticles in several types of molten inorganic salts (Nature 2017, DOI:10.1038/nature21041). They also propose a mechanism behind the new colloids’ stability.

Such nanoparticle colloids could improve the heat transport properties of molten salts, which are used as heat-transfer fluids in nuclear reactors and solar-energy facilities. The work could lead to new types of nanomaterials by making it possible to synthesize them in molten salts at temperatures much higher than are currently feasible with ordinary solvents. And the new colloids could result in more-efficient inorganic thermoelectric materials by enabling researchers to engineer them in new ways.

Over the past few years, Talapin and coworkers developed an improved understanding of the inorganic surface chemistry of different materials that enabled them to select combinations of materials that form stabilized colloids. They make stable colloid dispersions by transferring surface-modified nanocrystals from organic solvents to molten salts or by mixing modified-nanocrystal powders directly with molten salts. In this study, they incorporated metal, semiconductor, rare-earth, and magnetic nanocrystals into AlCl3/NaCl/KCl and six other types of molten inorganic salts.

Conventional colloids are stabilized by electrostatic or steric forces that prevent solute particles from aggregating. But Talapin’s group proposes a new mechanism for the stability of molten inorganic-salt colloids: Strong solute-solvent chemical bonds that form at the nanocrystal surface induce partial ordering of the molten salt around each nanocrystal. The researchers’ theoretical analyses and molecular dynamics modeling suggest that this induced ordering in the molten salt prevents the particles from combining.

Colloids expert Håkan Wennerström of Lund University says he remains skeptical for now about some technical details of the mechanistic proposal. However, he says, the study’s observations are “clear-cut and carefully made” and the chemical bonding-based mechanistic proposal is “convincing.” It’s important “for materials science and technical applications to have methods for handling metals, alloys, and semiconductor materials in the form of colloidal particles in a solvent that can take a high temperature like a molten salt,” Wennerström adds.

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