NEWS OF TH E WEEK
RULES LACKING FOR REACTIVE CHEMICALS CHEMICAL SAFETY: Inquiry faults company, regulators for deadly Texas explosion
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Fertilizer Co. explosion, the Chemical Safety & Hazard Investigation Board (CSB) returned to the West, Texas, community where the retail fertilizer warehouse had been located. There, at a public meeting on April 22, CSB released its preliminary accident report that proposes changes to federal laws overseeing reactive chemicals. CSB’s investigation found severe shortcomings in existing regulations and standards for ammonium nitrate at the federal, state, and county levels as well as a “failure by the company to take necessary steps to avoid a preventable accident,” CSB Chairman Rafael MoureEraso said. The West accident occurred when some 40 to 60 tons of ammonium nitrate fertilizer held in a wooden building caught fire NEWSCOM
The aftermath of the April 17, 2013, fertilizer facility explosion in West, Texas.
N THE ONE-YEAR anniversary of the West
BUILDING RINGS WITH LIGHT PHOTOCHEMISTRY: Catalyst pair forges
cyclobutanes enantioselectively
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Y COMBINING TWO CATALYSTS, researchers
have used photochemistry to build enantiomerically enriched rings in high yields. The advance could add to the tool kit for building motifs present in agrochemicals and pharmaceuticals. For more than a century, chemists have talked about
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O +
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Because it uses visible light, the new method works even with substrates with weak C–Br bonds.
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Ru photocatalyst, chiral Lewis acid catalyst Visible light
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Br
generating chirality with photochemistry because it can access products not available by other routes. But photochemistry’s march toward enantioselectivity has lagged behind those for transition-metal catalysis or organocatalysis. The reason is that once a molecule absorbs a photon of light, it reacts before it can be reined in by a stereochemistry-controlling catalyst, explains CEN.ACS.ORG
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and exploded, killing 14 people—12 volunteer firefighters and other emergency responders and two residents. Another 226 citizens of West were injured. Some 150 homes were destroyed by the blast, and twice that many were damaged. An apartment complex, three schools, a nursing home, and a hospital were also damaged. Moure-Eraso noted that Texas lacks a statewide fire code, which could have encouraged county fire departments to closely monitor safe storage and handling of chemicals. Such codes, CSB said, could have also kept populations away from hazardous facilities, such as the warehouse. The CSB investigation found that the community was largely unaware of the threat posed by the supply of ammonium nitrate in the warehouse, as well as another 100 tons that was held in a railcar adjacent to the facility. When built in 1961, the warehouse was surrounded by open fields, but CSB said that, over the years, homes, schools, and other buildings had been located nearby. In its investigation, CSB found that throughout the nation some 1,351 facilities, similar to the one in West, held ammonium nitrate fertilizer. Most are in 10 southern agricultural states. CSB proposed changes to federal laws, including adding reactive chemicals, such as ammonium nitrate, to substances regulated by the Environmental Protection Agency and Occupational Safety & Health Administration. It also recommended inherently safer design principles be required for these facilities.—JEFF JOHNSON
Tehshik P. Yoon, who led the new work. The few existing enantioselective options require specialized light sources or carefully designed catalysts. Yoon and his coworkers at the University of Wisconsin, Madison, reported in Science a different approach. Their method makes chiral cyclobutanes from the visible-light-promoted [2 + 2] photocycloaddition of α,β-unsaturated ketones (2014, DOI: 10.1126/ science.1251511). It requires two catalysts: Ru(bpy)3, a transition-metal complex that absorbs visible light, and a chiral Lewis acid made from the lanthanide element europium. “We’re using wavelengths of light that pass through organic molecules,” so they don’t enter the excited state that leads to willy-nilly reactivity, Yoon says. It’s Ru(bpy)3 that absorbs this light, which comes from a compact fluorescent bulb, and then “spits out an electron” to trigger cyclobutane ring formation, Yoon explains. The reaction occurs under chiral control because the chiral Lewis acid coordinates to the ketone substrate. The work cleverly mimics photosynthesis in that it decouples the harvesting of light energy from bondbreaking and bond-forming steps, explains University of Neuchâtel, Switzerland, chemist Reinhard Neier in an accompanying commentary (DOI: 10.1126/ science.1252965). “I think the concepts are general” and will yield more than just cyclobutanes, Yoon says.—CARMEN DRAHL
APRIL 28, 2014
