NEWS OF THE W EEK
ZEOLITES DON’T MIND HOT WATER CATALYSIS: Organosilyl groups
stabilize workhorse catalysts for aqueous-phase reactions
T
ACKING HYDROPHOBIC organosilyl groups
onto the surface of a common zeolite helps overcome the catalyst’s inability to function effectively when liquid water is the reaction medium, chemical engineers have found. The researchers believe their water-repelling zeolite could be a hit for high-pressure water/oil emulsion processing of biomass into fuels and chemicals. The protecting group strategy could also benefit other types of catalysts that are inhibited by water, they say. Zeolites are aluminosilicate materials with reactive acidic sites and are widely used in vapor-phase refinery processes. They have a low tolerance for hot liquid water, however, which causes them to lose their crystallinity and catalytic activity. COURTESY OF DANIEL RESASCO
Zapata (from left), Faria, and Resasco examine a biphasic solution from a high-pressure reaction using their hydrophobic zeolite catalyst.
EVANS WINS WELCH AWARD AWARDS: Harvard chemist’s contributions to asymmetric synthesis recognized with 2012 prize
TATI ANA BLANCO/ WE LC H FOUNDATI ON
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Evans
OR HIS PIONEERING WORK in synthetic or-
ganic chemistry, Harvard University chemist David A. Evans has won this year’s Welch Award in Chemistry. The $300,000 award is given annually by the Houston-based Welch Foundation to foster basic chemical research that benefits humankind. “David Evans is one of the world’s best synthetic chemists,” says fellow organic chemist Marye Anne Fox, chair of the Welch Foundation’s scientific advisory board and chancellor of the University of California, San Diego. “His inventive mechanistic work brought clarity to new approaches to the catalytic induction of asymmetry in complex chiral molecules.” Evans, 71, is best known for devising a family of chiral oxazolidinone auxiliaries that can be used to control a target structure’s stereochemistry. These readily available and flexible asymmetric reagents are widely used in both industrial and academic laboratoWWW.CEN-ONLIN E .ORG
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Paula A. Zapata, Jimmy Faria, Daniel E. Resasco, and coworkers of the University of Oklahoma, Norman, reasoned that studding a zeolite’s external surface with hydrophobic octadecylsilyl groups would hinder diffusion of water into the zeolite’s pores and prevent the collapse of the framework structure (J. Am. Chem. Soc., DOI: 10.1021/ja3015082).They found by an assortment of X-ray, spectroscopy, and microscopy methods that untreated HY zeolites begin to fall apart within a few hours at 200 °C in aqueous reactions, whereas their functionalized HY zeolite retains its crystallinity, surface area, porosity, and density of reactive acidic sites under the same conditions. The Oklahoma researchers tested the catalysts in common biorefinery reactions, such as dehydration of 3-pentanol to pentene and 2-propanol to propylene, as well as alkylation of m-cresol with 2-propanol. The functionalized zeolite outperformed unfunctionalized zeolites in product yield. It also was better in stabilizing the water/decalin biphasic reaction medium, which helps separate the products and recycle the catalyst. The new zeolite “could represent a big step for biomass conversion,” says George W. Huber of the University of Massachusetts, Amherst, an authority in biomass processing. “Aqueous media is a great way to convert biomass into fuels and chemicals, because most biomass components are water soluble,” Huber notes. The Oklahoma team’s results “now suggest a way to modify zeolites so they can be used in water,” Huber says.—STEVE RITTER
ries for natural product synthesis and drug discovery. Evans has dozens of other useful synthetic methods to his credit, including a variety of enantioselective transformations as well as sigmatropic rearrangements and hydride reductions. He’s also made fundamental contributions to organosilicon and organosulfur chemistry. The power and versatility of Evans’ construction methods are clear from the more than 50 natural products his lab has synthesized over the years. Many feature dizzyingly complex stereochemistry, such as the glycosylated antibiotic vancomycin and the anticancer agent bryostatin. “But I believe my greatest achievements have come in education,” Evans says. More than 70 of his students have gone on to start their own independent academic labs. He says he was inspired to be an educator by physical chemist Norman C. Craig of Oberlin College, where Evans earned a bachelor’s degree in chemistry in 1963. After earning a Ph.D. in chemistry from California Institute of Technology in 1967, Evans taught at UCLA and Caltech before moving to Harvard in 1983. His previous honors include the American Chemical Society’s Arthur C. Cope Award and election to the National Academy of Sciences and the American Academy of Arts & Sciences. Evans says the award money will go a long way toward covering college expenses for his two grandsons, now ages 14 and 11.—AMANDA YARNELL
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