Over the years that I’ve been involved with synthesis the solvents I’ve used for reactions and work-ups have changed quite drastically and, unfortunately, I seem to be going backwards according to the solvent selection guide.
Just a scribble graph of solvent use over time.
My “gateway” solvents (heptane, toluene, acetonitrile, ethyl acetate) seem to have led me on a downward spiral towards the environmentally nasty DCM. This is a result of a combination of lazyness and necessity. While at Pfizer, I simply didn’t use any halogenated solvents except for CDCl3 and very very very occasional DCM for sample prep. It just wasn’t hanging around on the bench and the rotavaps were perfectly capable of taking off toluene and ethyl acetate, unlike some found in academic labs. The process solvent choice thing hung around with me through my masters project but I did resort to DCM for some reactions and work-ups. Through the DPhil, my main reactions were carried out in 1,2-DCE but this accounted for a small amount of solvent per reaction. Methodology work with usually only 1-2.5 mL of solvent doesn’t work out to much even when you’re doing hundreds of reactions. Later on we did change this to propylene carbonate which is a solvent that I really enjoyed using. It is probably worth trying out in more reactions and recrystallisations. I did still try to use more benign solvents for most of the starting material synthesis. With no 2-Me-THF, TBME, or MeCN about (this was around the time when acetonitrile production stopped for a while), THF and diethyl ether became the general work horses.
I’ve always been one to avoid columns if I can possibly help it but of course I do need to use chromatography. My column solvents changed from ethyl acetate/heptane at Pfizer to EtOAc/60-80 petrol to ether/40-60 petrol to pentane. Switching to lower bpt solvents mostly to get rid of persistent solvent residues in the annoying oils/gums that I was producing at the time. Column waste is something that is particularly rife in academic labs. People generally use way too much silica for most separations and then use inappropriate solvent systems and then complain that their columns take so long.
Now I’ve somehow slipped into using DCM pretty regularly. MeOH/DCM is being employed too readily but at least my DCM squeezy bottle isn’t around anymore.
Yes yes, DCM is cheap and a great solvent but it’s disposal isn’t. Do any (academic) departments out there charge disposal costs to the individual research groups depending on use?
[I just noticed this topic has recently been discussed over at Org Prep Daily]