Accidents spark some researchers to switch to safer method of purifying organic solvents
Last July, a fire in the lab of chemistry professor William J. Evans at the University of California, Irvine, caused $3.5 million in damage and seriously burned a graduate student. The student was performing a task that he had done hundreds of times before--purifying an organic solvent using a reflux/distillation apparatus, or solvent still--when hot benzene escaped from the apparatus and ignited.
Although it may have been the most costly, the UC Irvine fire was not the first accident involving organic solvent purification; many researchers have experienced fires, floods, or spills. "The potential for major disaster with solvent stills is quite large," says Steven W. Baldwin, an organic chemistry professor at Duke University. "I think we're operating on borrowed time."
Many organic and organometallic reactions require solvents that are free of water and, sometimes, free of oxygen. Classically, solvent purification is accomplished by refluxing the solvent in the presence of sodi-um or potassium metal and benzophenone in an inert atmosphere. The reactive metal removes moisture from the solvent, and the ketyl intermediate that forms upon reaction of the ketone and the metal helps to sop up any oxygen. The blue color of benzophenone ketyl is used as an indicator that the solvent is ready for use.
Some labs commonly require several liters of each of four or five different water- and oxygen-free solvents per day. To meet demand, many liters of each solvent are allowed to reflux for long periods of time, much of it unattended.
Having large quantities of flammable solvent around the lab is a safety concern in and of itself, but dangers inherent in the reflux/distillation solvent purification process exacerbate the hazard. The setup requires electrical equipment such as a heating mantle and a vacuum pump--either of which can create a spark. In addition, if even a small piece of reactive metal escapes during purification or cleanup, the moisture in the air can be sufficient to ignite the metal.
The dangers of the conventional method for solvent purification spurred chemistry professor Robert H. Grubbs of California Institute of Technology to seek an alternative. In collaboration with Dow, Grubbs published a method relying on activated alumina and a copper catalyst to remove moisture and oxygen from organic solvents [Organometallics, 15, 1518 (1996)]. A number of firms, including Newburyport, Mass.-based Innovative Technologies, now offer systems based on Grubbs's method.
Although the dangers of handling flammable solvents remain, these safer systems operate at ambient temperatures and don't require reactive metals. Instead, dry nitrogen or argon is used to force solvent over columns containing moisture-scavenging activated alumina and oxygen-scavenging copper catalyst. Columns can be scaled up or down as needed, but each must be dedicated to a single solvent. A few solvents--ether, tetrahydrofuran, and methylene chloride--are compatible with activated alumina but not with the copper catalyst. Oxygen must be removed from these solvents by purging them with dry nitrogen or argon.
The potential for accidents like the one at UC Irvine has pushed many big universities and companies to abandon solvent stills. The alternative systems are ubiquitous at Massachusetts Institute of Technology and Caltech. At the time of the accident at UC Irvine, Evans had already switched four of the most popular solvents in his lab to the new systems.
But even though the column-absorption systems clearly win the safety debate, not everyone has made the switch. Researchers at some colleges and universities, as well as some smaller chemical and pharmaceutical companies, have stuck with conventional solvent stills.
ONE BIG REASON is price. Researchers must pony up approximately $4,000 to $5,000 per solvent to replace their stills with the commercial systems. And although hundreds of liters of solvent can be purified per column, replacing the packing costs about $200 per column. "Money is the deciding factor for departments making these decisions," Grubbs says.
But should safety concerns outweigh the costs? "Since there is a safer solution available, when there is a problem, the university really opens itself up to liability," Baldwin argues. "Institutions should provide both a mandate and incentive" to make the switch, he says.
Funding safety measures at universities has always been contentious. "Ideally, safety is part of the infrastructure of doing business in the institution," says Stanley H. Pine, a professor emeritus of chemistry at California State University, Los Angeles, and a member of the investigation team for the UC Irvine fire. "And, therefore, it should come from the top." Pine suggests that the university administration, the chemistry department, and individual researchers should share fiscal responsibility for the new systems.
The potential for serious injury and expensive damage demands researchers seriously consider switching to the new systems, Baldwin says. "A single disaster would cost infinitely more than replacing the stills with what is now available."
>> Get a safe Solvent Purification system