Benzene at 200
rigb.org> its carcinogenic effects are now well known (no more using it to decaffeinate coffee, degrease engines, or in shaving cream, thankfully!)
I had no idea benzene was used to decaffeinate coffee [1]. Solvent separation makes sense, but I'd never really thought about it. Definitely not a residue I'd want to drink.
From an amateur chemistry perspective, benzene is so fascinating. Benzene rings are one of the first, maybe the very first, structures students learn that don't have fixed, discrete bond counts. That they can be interpreted as a cloud of 1.5-electron bonds between each of the 6 carbons, or alternating double- and single-bonds, makes for some interesting hand analysis of molecules.
[1] https://en.wikipedia.org/wiki/Decaffeination#Direct_method
This was done before roasting. Benzene is volatile even at room temperature and the roasting process almost certainly removed it all. I think the concern was more about industry workers or the environment than the consumer. And maybe about the optics of using a particularly nasty chemical to prepare your food or drink.
From what I understand chemicals were analogous to computer internet technology at that time. A lot of rapid development of new things that went on to fundamentally change society- the modern world relies on synthetic chemicals and no one really remarks on their existence these days.
Also that Benzene led to the creation of the field of organic chemistry.