Dichloromethane, or DCM, is a common solvent used in industrial applications as well as organic chemistry labs. Used by generations of organic chemistry students to dissolve pain reliever tablets before isolating the compounds in a mixture, DCM was recently banned by the U.S. Environmental Protection Agency for most uses.
The 2024 EPA ban would require schools to closely monitor its use, effectively preventing it from being used in student labs with large numbers of beginner chemists. Now, the solution devised by chemists at Dartmouth has garnered national attention.
"Everybody recognized right away that finding a substitute was the only real choice," said Steve Wright, a teaching assistant for Introductory Organic Chemistry.
DCM is immiscible and non-flammable, making it an ideal candidate for separating and extracting compounds in teaching labs. However, DCM is also a known carcinogen. Despite alternatives being around for a while, many labs have been reluctant to switch.
"It's not trivial to change out solvents for reactions," added senior lecturer Cathy Welder. "You change one thing, and you often have to change something else."
Tasked with finding an alternative, Wright quickly zeroed in on ethyl acetate and MTBE as a potential replacement solvent for the infamous pain reliever and wintergreen oil labs. Later experiments demonstrated that ethyl acetate worked well as a stand in for DCM. The new solvents were introduced to the teaching lab this year, with the main adjustment needed being an adjustment to the time needed to finish the lab. "It takes students a little longer," added Welder. "They just have to wait their turn to evaporate the solvent on a rotary evaporator."
"What happens in student labs doesn't necessarily translate into research labs," concluded Dartmouth Professor of Chemistry Ivan Aprahamian. "Nonetheless, every chemistry department in the country will have to change the way they run their undergraduate organic labs, and this article will guide them through the process."