Organosulfur compounds include some of the sweetest and the worst smells known to science. Thioacetone is the worst of them all.
Humans have adapted to be excellent sulfur detectors, especially when that sulfur is part of an organic compound. This adaptation helps us to smell when food has spoiled, and can warn us of low oxygen levels underground. As a consequence, we find organosulfur compounds to be some of the smelliest in the world.
On one hand, the sweetener saccharin is derived from an organosulfur compound. Some of the flavours of wine, cheese, chocolate, and coffee are organosulfuric in nature, not to mention onion and garlic. On the other hand, mustard gas and acid rain are as well.
Thioacetone, however, is on a completely different level. It is derived from acetone (nail polish remover) and is perhaps the stinkiest smell in the world. It was first synthesized in a German lab in 1889. Its effects were immediate: people who smelled it got nauseous, vomited, and often passed out.
So far so bad, but it gets worse. The German lab began with just 100ml of acetone, less than half a cupful. The resulting thioacetone spread its spell out of the lab, across the street, and into the city. People were smelling it and reacting to it three quarters of a kilometre (half a mile) away.
And it gets worse! Adding water to the mix just makes it stronger and more penetrating, according to some British chemists who tried the same thing in 1890. They described the smell of thioacetone (I love this description) as “fearful.”