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2-Propionyl-1-Pyrroline (Who's making popcorn again!?)

By moleculeoftheday on April 10, 2007.

I have a love-hate relationship with microwave popcorn. It can be tasty from time to time. It can be absolutely nauseating, however, at 10am on a Wednesday when someone at work decided to make it for some reason, leaving the office smelling like a movie theater all day. Let's not even talk about the people who let it burn. Part of the reason for popcorn's ability to "carry" is 2-propionyl-1-pyrroline, which can be smelled at incredibly low concentrations.

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The compound has a reported odor threshold of 20 picograms per liter, which is 20 parts per quadrillion. Contrast t-butylmercaptan, which is such a profound odorant they use it as a warning chemical in natural gas - its odor threshold is about five orders of magnitude higher, or 2 parts per billion (75 page PDF, see page 10).

Hopefully this helps explain why you can smell that stuff all the way across the building. Other odorants, such as the cloyingly buttery diacetyl, no doubt play a role (diacetyl is no slouch, with an odor threshold in the 10's of ppb). I enjoy my popcorn, but I can't say I haven't fantasized about a world where we'd use, say, 2P1P as the natural gas odorant and ban popcorn for safety reasons.

Anybody smelled it neat?

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food

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I enjoy reading this blog, brings out the chemistry geek in me! One note, picograms per Liter is actually parts per quadrilion, one liter being a 1000g makes it a femtogram (10^-15)/gram.

Also, diacetyl is incredibly harmful from an occupational exposure standpoint, leading to "popcorn lung" among workers. Check out this blog for more.