Don’t mix sodium hydride with polar aprotic solvents

Combining sodium hydride with some solvents can be a bad idea, as a group of researchers from Corteva Agriscience and Dow Chemical remind the chemistry community in Organic Process Research & Development ,(2019, DOI: 10.1021/acs.oprd.9b00276). An intact calorimetry cell (left) and a ruptured cell the authors used to study the explosive risk of NaH in DMSO. These cells typically rupture at pressures in excess of 1,000 bar. Credit: Org. Process Res. Dev. Reports of explosions from combining NaH with a polar aprotic solvent such as dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc) go back at least to 1966: Sodium hydride-DMSO mixture explodesA violent pressure explosion occurred during the preparation of methylsulfinyl carbanion by a scheme involving the addition of sodium hydride to an excess of dimethyl sulfoxide. Scientists at the Cancer Chemotherapy Research Department of Mount Zion Hospital and Medical Center (Palo Alto, Calif.) were scaling up a seemingly effective method of C-methylating heteroaromatics [J. Org. Chem., 31, 248 (1966)]. When the CCR chemists tried a mole ratio DMSO (2.15) : sodium hydride (0.41) : isoquinoline (0.40), the methylation was incomplete. And it did not explode.In the next experiment, 4.5 moles of sodium hydride were added, in five portions during three hours, to 18.4 moles of DMSO. The reaction was kept at 70 °C. and mechanically stirred. After an hour, solution was complete. Then, however, the temperature increased slightly and a greenish solid began to separate. The reaction was cooled, but the temperature rose sharply and after a few seconds the explosion occurred. A noxious gas filled the laboratory and a water-soluble, viscous, polymerlike material coated the hood and its contents.Frederick A. French of the Cancer Chemotherapy laboratory says that he knows of no previous mishaps with solutions of alkaline reagents in DMSO. However, the hazards from acidogenic reagents, such as acid chlorides and halomethyl ketones, and DMSO are well known, he notes.C&EN April 11, 1966, page 48 From C&EN's story about the new OPR&D paper: Yang and coworkers also investigated the chemistry that makes these combinations unsafe. Yang says that radical reactions between the base and the solvents can generate gases, including dimethylsulfide and ethylene in the case of NaH added to DMSO. . . . [Yang] points out that there are alternatives that can perform the same chemistry, although there is no combination that can be universally applied as a substitute. Tetrahydrofuran could be used as a solvent with NaH, and there are alternative bases, like alkoxides and hydroxides. “But scientists have to understand the stability of these bases with the solvents as well,” Yang says. C&EN Aug. 19,...

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Liquid nitrogen calamities

Credit: Shutterstock Via @sarahdcady on Twitter, some liquid nitrogen stories from 2006. One wasn't quite a calamity--but it easily could have been. Down the stairs at the University of California, Berkeley: Yesterday the LeConte elevator was out of order, which for most of us would have meant taking the long way around. However, one undergrad, tasked with transporting a full 230 L dewar, simply decided to take the stairs.At about 80% the density of water, 230 liters of liquid nitrogen weighs about 400 pounds, not counting the additional weight of the steel vessel containing it. When rolled onto the stairs, the dewar promptly tipped over and plummeted downward on its side, knocking deep gouges in the marble steps and dragging along the unfortunate student, who inexplicably held on as his cargo began to tumble. Miraculously both student and dewar arrived at the landing without rupturing, but the dewar was still on its side and pressure was building up.This was the situation when we got the frantic call from the building manager; once enough of us arrived at the scene we were able to pull the dewar upright and release the pressure. This averted any imminent explosion, but now we had a different problem: 400 pounds of liquid nitrogen stranded on a landing between the ground and first floors. Suggestions were floated including emptying the nitrogen out the nearby window, but ultimately we found another dewar which was wheeled to the top of the stairs on the first floor, and the nitrogen was transferred there through a long hose. The empty dewar was then carried up the stairs, a task requiring four men and gouging new (but shallower) grooves in the staircase. When metal plugs replaced pressure relief and rupture disks at Texas A&M University: The cylinder had been standing at one end of a ~20′ x 40′ laboratory on the second floor of the chemistry building. It was on a tile covered 4-6″ thick concrete floor, directly over a reinforced concrete beam. The explosion blew all of the tile off of the floor for a 5′ radius around the tank turning the tile into quarter sized pieces of shrapnel that embedded themselves in the walls and doors of the lab. The blast cracked the floor but due to the presence of the supporting beam, which shattered, the floor held. Since the floor held the force of the explosion was directed upward and propelled the cylinder, sans bottom, through the concrete ceiling of the lab into the mechanical room above. It struck two 3 inch water mains and drove them and the electrical wiring above them into the concrete roof...

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10 years ago, Sheri Sangji died following a lab fire
Jan16

10 years ago, Sheri Sangji died following a lab fire

Today is the 10th anniversary of Sheharbano (Sheri) Sangji's death from injuries sustained in a laboratory fire at the University of California, Los Angeles. From C&EN: Her death pushed some chemists to try to improve academic lab safety culture to prevent similar accidents at their own institutions and beyond. C&EN asked scientists from all corners of the chemistry community to describe their efforts. Read on for their strategies, including incorporating safety into chemistry education, improving training, and developing resources to help people work in a safer manner. Yet large-scale, systemic change remains elusive, as demonstrated by grievous incidents in the decade since Sangji’s death. Postdoctoral researcher Meng Xiangjian died in a hydrogen explosion at Tsinghua University in 2015. Graduate student Preston Brown lost three fingers and damaged his eyes in a nickel hydrazine perchlorate explosion at Texas Tech University in 2010. And postdoc Thea Ekins-Coward lost one of her arms in a hydrogen-oxygen gas mixture explosion at the University of Hawaii at Manoa in 2016. Adding to that list, in early December one researcher was killed and three others were injured in what seems to have been an explosion of a hydrogen-oxygen gas mixture at the Indian Institute of Science's Laboratory for Hypersonic and Shock Wave Research. A few weeks later, three students died in an explosion involving sewage treatment experiments at Beijing Jiaotong University, according to local news reports. And those are just the incidents that C&EN knows about that involved deaths or significant permanent injuries. Many others had milder consequences, though they could've easily been worse. To learn more about how to improve laboratory safety culture, particularly in academic research labs, read C&EN's...

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Gas cylinder explosion in India’s premier government lab kills 1 person, wounds 3 more
Dec31

Gas cylinder explosion in India’s premier government lab kills 1 person, wounds 3 more

Contributed by K. V. Venkatasubramanian, special to C&EN. A gas cylinder blast in a laboratory at the Indian Institute of Science (IISc) on Dec. 5 killed one researcher and left three others grievously wounded. The researchers were working in the Laboratory for Hypersonic and Shock Wave Research, which was established in the 1970s to study shock waves. Vikram Jayaram, head of IISc’s internal investigation team, told C&EN on Dec. 31 that the explosion involved cylinders containing hydrogen-oxygen mixtures that are used to generate controlled shock waves in a protected, closed container to study granite fragmentation for purposes such as mining and oil recovery. "At this stage of the inquiry, all indications are that adequate safety precautions were employed," Jayaram said. Manoj Kumar, 32, died instantly. Naresh Kumar, Atulya Uday Kumar, and Karthik Shenoy were hospitalized. All were project engineers employed by start-up Super-Wave Technology, an IISc initiative managed by aerospace engineering professors K. P. J. Reddy and G. Jagadeesh. The company researches shock waves and their applications. Police booked the two professors on Dec. 6 on charges of causing death due to negligence and for causing grievous injuries by acts endangering the lives and personal safety of others. UPDATE: This story was revised on Dec. 31, 2018, to incorporate new information from Vikram...

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“Expertise is deeply gratifying, but it is also a potential trap”

From last week's issue of C&EN, some lessons learned by ACS President Allison A. Campbell following a bicycle crash in Washington, D.C., and how they relate to laboratory safety: Since I regularly ride near my home in Washington state, I know the trails there quite well, including the overall quality, locations of potholes, and other hazards to be avoided. Additionally, we don’t get much rain, so it did not occur to me to pay any particular attention to puddles on the trail. So as I rode through a large puddle that morning, I was surprised when my front wheel dropped into a deep crater, sending me hurtling over my handlebars. My nose and chin slammed against the trail’s packed-gravel surface. I picked myself up slowly, stunned, stinging, and bleeding profusely. I was, all in all, fortunate. Even though I felt fine, I made a visit to the emergency room. I had neither a concussion nor broken bones: only scrapes, bruises, and two front teeth that were slightly pushed in but easily straightened. ... We are all experts of one form or another, whether in the laboratory, the office, the kitchen, or any number of other settings. Expertise is deeply gratifying, but it is also a potential trap when it leads to overconfidence and a false sense of familiarity. Since my accident, I have been thinking about the idea of the “beginner’s mind” popularized by the Zen monk Shunryu Suzuki back in the 1970s. Suzuki observed that, as beginners in any practice, we are fully present and humble as we dedicate ourselves to learning something new and are on guard to grasp things we don’t know or might miss. As we accumulate skill and experience, the intensity of our awareness tends to erode. Suzuki urged us all to nurture our beginner’s mind, regardless of how advanced we might become at our pursuits, and to recognize that we are always beginners. Until recently, I had not thought about Suzuki’s advice as practical safety guidance. Read Campbell's full column at...

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Hazards of high oxygen concentration, mixing incompatible materials, and more in process safety newsletters
Aug01

Hazards of high oxygen concentration, mixing incompatible materials, and more in process safety newsletters

From AIChE’s "Process Safety Beacon" newsletters: Hazards of high oxygen concentration - "Autoignition temperature (AIT) and minimum ignition energy (MIE) are lowered markedly by higher oxygen content. Substances ignite more readily, burn faster, generate higher temperatures, and are difficult to extinguish." Mixing incompatible materials in storage tanks - "Understand potential hazardous interactions among different materials that you unload into your plant’s storage tanks. The July 2016 "Beacon" describes the “Chemical Reactivity Worksheet,” a tool which your engineers and chemists can use to help understand chemical interactions." …but the temperature was below the flash point! - "Because the vessel was operating below the flash point of the contents, the concentration of fuel vapor in the vessel atmosphere was too low for ignition. There should not have been an explosion hazard. But the fuel may not only be present as a vapor (remember dust explosions). The investigation determined that the vessel agitator created a fine mist of liquid droplets (Fig. 2). The tiny droplets were estimated to have an average size of about 1 micron. ... Flammability testing demonstrated that the mist could be ignited at room temperature in air – and the mist would be ignited even more easily in a pure oxygen atmosphere." Are you sure that vessel is empty? - "When returning equipment to service following maintenance, make sure that it is completely clean and does not contain anything that could be incompatible with process materials or operating conditions." Corroded tanks! - "Holes in tanks can allow toxic or flammable vapors to escape into the surrounding environment. Corrosion can weaken tanks, pipes, or other equipment so they can fail under normal operating conditions." Incident investigation of a steam pipe failure - "There is a reason for including a team of people with different expertise in an incident investigation... In this incident, the engineers and other experts did not recognize the machine tool marks on the failed pipe, and yet it was immediately obvious to the expert, experienced machinist. His knowledge completely changed the conclusions of the investigation, and was essential for understanding the cause of the...

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