Molecule of the Day

Sulfur usually stinks. Previously, I’ve covered ammonium thioglycolate, mercaptoethanol, and dithiothreitol, all of which are used to break up S-S bonds in biomolecules. The S-H group is what does the job here, and where this functional group is found, stink is usually nearby. The above thiols all have some degree of stink.

Not all thiols stink. Previously, I’ve covered a grapefruit thiol, a fruity thiol, and a coffee thiol.

Methanethiol is not one of the nice-smelling thiols. With a smell most often described as rotten cabbage or rotten eggs, you’d think it was useless. You’d be wrong.

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Because it smells so terrible, it’s a great warning indicator for something that shouldn’t be escaping into the atmosphere – such as natural gas. You can smell methanethiol down to the parts per billion level – that is, micrograms per liter. We add it to natural gas (which is mostly odorless methane) for just this reason.

Interestingly, farts often contain methane and hydrogen – flammable natural gas components, as any frat boy with a lighter can tell you. Additionally, their odor is partly caused by methanethiol (as well as other stinkies like hydrogen sulfide and indole). One quasi-renewable energy source is so-called “landfill gas” – essentially a landfill fart:

Municipal solid waste contains significant portions of organic materials that produce a variety of gaseous products when dumped, compacted, and covered in landfills. Anaerobic bacteria thrives in the oxygen-free environment, resulting in the decomposition of the organic materials and the production of primarily carbon dioxide and methane.

In a related vein, here is a video of Prof. Dr. Ross Eustace Geller explaining methanethiol doping of natural gas.

Of course, he messes it up by contending methane is not natural gas, but a different, smelly gas, which is false. But what do you expect from a sitcom professor who you’ve never seen working on a grant proposal?

Comments

  1. #1 mitch
    March 18, 2009

    He is a paleontologist not a chemist.

  2. #2 Dennis
    March 18, 2009

    “You can smell methane down to the parts per billion level – that is, micrograms per liter.”

    You must have been thinking too much about the Friends clip and left the “thiol” part out.

  3. #3 Molecule of the Day
    March 19, 2009

    Fixed, thanks.

  4. #4 psi*psi
    March 19, 2009

    One of the research groups at my uni was working with a lot of thiols a few years back, which was only annoying to people IN the lab…until the fume hoods were fixed.
    Then they managed to get four buildings evacuated downwind on suspicion of a gas leak.
    …Then they stopped working on that particular project.

  5. #5 LtStorm
    March 19, 2009

    Trying to explain to the layman that just because they smell a thiol doesn’t mean there’s a gas leak is always fun. A few weeks ago the computer in my office crapped out on me, and I had to call the IT department. The lab across the hall uses thiol esters for stuff they work on, so there’s the constant aroma associated with natural gas floating in the hall.

    I spent longer explaining to the tech what he was smelling wasn’t natural gas (and the smell associated with natural gas not actually *being* the gas) than it took him to actually fix the computer.

  6. #6 antediluvian
    March 19, 2009

    Psi…funny thing is we used to have the fire department enter the building every other week when the engineering department would complain about a potential gas leak.

    The compound that caused the problem was TMS-S-TMS and was used on the mg scale. It was enough to open the 1 g bottle syringe out 50 mg and quickly recap to get the fire department active during a breeze.

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