Polyphosphoric Acid (Burning honey)

Polyphosphoric acid is a mixture of phosphoric acids and its anhydrides:

I like it as an acid catalyst in organic synthesis - a lot of people hate it because it's so thick and hard to handle. The stuff is absolutely gooey mess; when you heat it up, it gets down to about the consistency of honey. The neat thing is that lots of stuff will go into it (it is a strong acid goo, after all), but once you quench your reaction with water, your stuff will often crash out.

During a blissful few months, I cranked out a series of Fischer indoles with the stuff. Everything seemed to work!