I had a lot of long days when I was a teaching assistant. One semester I had three lab sections of sophomore organic chemistry to TA, and sometimes after the first lab of the week I knew that I was in for a rough ride.
Such was the case when we took the students through the good ol' Grignard reaction, as I mentioned here. The problem wasn't the reaction (I have to admit that I can't remember what we had everyone quench the reagent with, actually). The problem was the ether. We didn't have nearly enough fume hood space for all these reactions, so out on the bench tops they were. Two dozen steam baths hissing and gurgling, two dozen round-bottom flasks belching out ether vapors. By the third run-through of the week, I was teaching the lab section from out in the hall, trying to avoid another whiff of the damn stuff so I wouldn't have to run back in and puke in the sink.
The isoamyl acetate synthesis was another one in that vein. That's banana ester, the source of all the cheap, penetrating, one-note artificial banana flavor in the world. It's a pretty dramatic demonstration, in its way, because isoamyl alcohol and acetic acid (the starting materials) smell nothing like bananas, believe me. The workup was extraction with saturated sodium bicarbonate, a perfectly reasonable thing to do since there's an acid catalyst in the reaction.
But you do have to remember to vent the separatory funnel, oh yes. Close the stopcock, pour everything in, put in the stopper, shake it around - but never forget that shaking acid around with bicarb makes plenty of fizzy carbon dioxide. Especially don't forget about it until you've shaken the thing for, like, a minute and a half. And then open the stopcock. While it's pointed at your lab partner. This poor girl comes up to me with this huge stain all over the front of her dress, smelling like a shipwrecked banana boat, saying "I think I need to go back to the dorm and change".
The other thing that I can't help remembering is the day we had everyone do an oxidation with nitric acid, glucose to gluconic acid, I believe. Now, no one does that any more, at least since Emil Fischer keeled over from tasting his own compounds (a fact his Wikipedia article neglects to mention; I should edit that in there). And I'm not sure why that experiment was even in the lab curriculum. We did manage to get everyone into the fume hoods for it, though, thank God, except for one lunatic. He hauled his beaker of hot nitric goodness over to me, stuck it under my nose, and asked "Is this done yet?" I was coughing for three days. No matter where I end up over the next few months, at least no one's going to do that to me.