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Derek Lowe The 2002 Model

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Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases. To contact Derek email him directly: Twitter: Dereklowe

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February 18, 2007

Wake Up and Smell the Solvents

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Posted by Derek

It's now been nearly three weeks since I smelled any ethyl acetate or acetone. Those were the two last vapors I was exposed to in my former lab, as I cleaned out some dirty flasks, and those are two of the most common solvents that organic chemists breath in. Neither of them is particularly hard to deal with - acetone has a clear, penetrating solvent-y smell, and ethyl acetate, as a typically fruity ester, comes close to being pleasant. There's plenty worse out there. Hexane and methylene chloride are all over the place in a typical synthetic lab, too, and they're a bit less appealing with their flat paint-cleaner character. (They're rather less appealing from a toxicology standpoint too, for that matter).

Of the other common lab solvents, THF has a rather pungent ethereal smell - not something you'd line up for, by any means, and diethyl ether itself fills up your nose with great speed and thoroughness. Somehow, there's rarely a thin whiff of ether in the air - it's either nothing or a choking blanket of the stuff. Acetonitrile is something you'd think would have an interesting reek, but it defies expectations (and breeds doubt as to the broad-spectrum utility of the human nose) by having absolutely no smell at all.

Many of the really polar solvents have that feature. DMF has a smell to it, but it's surely traces of dimethylamine that account for most of it - in my experience, the pure stuff doesn't have much character at all. DMSO is the same way. There's something oddly scented there, and you can tell as it takes up olfactory room that you're not smelling regular air, but it's not as strong as you'd figure. As with DMF, you have to wonder how much is due to traces of impurities, such as reduced sulfur compounds, of which it wouldn't take much.

And the most pleasant of the bunch? Pure ethanol, for my money. It's not pleasure by association, either, because I don't really drink at all (and never have). But straight ethanol's combination of fruitiness and pungency is unique and appealing. Its cousins don't make the cut. Methanol's dim and harsh, and the propanols are no improvement: n-propanol (an uncommon solvent) is rather nasty, and isopropanol (the well-known rubbing alcohol smell) is not unpleasant, but rather strong, clinical, and somehow alien. n-Butanol, for its part, is quite foul in the manner of butyl compounds everywhere. Our noses have it in for straight four-carbon chains, and there's nothing to be done about it. Nope, it's ethanol, and it's not even close. Any other nominations?

Comments (61) + TrackBacks (0) | Category: Life in the Drug Labs


1. aa on February 18, 2007 11:45 PM writes...

Toluene is the best smelling solvent. stronger than benzene, fairly heavy and instantly noticeable. for reactions that aren't finicky about the solvent, i'll run them in toluene just to get a whiff. also, i'm i crazy or does acetonitrile have a faint popcorn-like odor? (i'm not saying it smells just like popcorn, but maybe like what your microwave smells like after you just whipped up some Orville Redenbacher)

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2. Anonymous on February 18, 2007 11:51 PM writes...

Isopropyl alcohol does smell pretty good outside of a clinic... toluene cannot be good for you , though

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3. bob on February 19, 2007 12:41 AM writes...

I also rather enjoy toluene, damage to my brain notwithstanding. Ethanol is, as mentioned, quite pleasant and I sometimes use it when i-Pr or methanol would also do just for the smell. I don't mind ether either, provided it's not in gagging concentrations. THF is somewhat unpleasant and I dislike i-PrOH. Ethyl acetate gets gagging-level nasty when you have high concentrations of it floating around (column).

Of course, then there were the reactions I ran in thiophenol (large scale). "Burnt ass" is the best way I heard it described.

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4. Paul on February 19, 2007 12:47 AM writes...

The smell of toluene gives me awful headaches. Benzene and o-dichlorobenzene are nice and fruity, but that's just the sweet smell of cancer.

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5. molecularArchitect on February 19, 2007 1:14 AM writes...

I must be weird, always the smell of liked methylene chloride and benzene. A shame that sniffing them is not a good idea. On the other hand, ethyl acetate in small doses is pleasant but more concentrated doses make me nauseous.

I went to school when steam baths were common and most reactions (at least in undergrad teaching labs) were not run in hoods. Labs back then used to reek of ether and amines. When I got to industry, I was surprised at the lack of odors. To some degree, I missed them! I still miss having a steam bath, the best and safest way to heat solvents for recrystallizations.

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6. Mark on February 19, 2007 3:46 AM writes...

THF is the best, IMHO.

The worst? C5H5N... pyridine...

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7. Lou on February 19, 2007 5:11 AM writes...

Though I don't use solvents much (apart from ethanol and methanol), the highlight of making an acrylamide gel for me is the use of n-butanol.
(Acrylamide gels can come in two layers, the lower resolving and upper stacking gels. To get a smooth straight interface between the two gels when setting the resolving gel, I put in water-saturated n-butanol.)

It definitely beats the nasty fishy amine smell of TEMED, which is used as catalyst to the acrylamide polymerisation reaction.

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8. Jalfrezi on February 19, 2007 6:03 AM writes...

I used to work in an industrial paint factory and there when a 1000 litre pan of toluene-based road paint fell off a forklift there was a surprising stampede of volunteers to help clean up the spillage.
As a lowly lab technician, one of my roles was to fetch the more esoteric solvents from the racked drums outside - MIBK (i think) was bottom of my list....

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9. Insider on February 19, 2007 6:13 AM writes...

Good grief! Are chemists just a bunch of "closet huffers"?

Seriously though. I do believe that the sense of smell is one of our least appreciated senses.

It certainly can be the most evocative.

Happy Presidents Day.

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10. milkshake on February 19, 2007 6:31 AM writes...

Acetonitrile smells to me very faintly like cyanide - but it is a extremely thin smell. Pure DMF has oily musty smell, not very strong one, and if you smell fishies it means dimethylamine is in it so I don't use such bottle for amide coupling.

My favorite solvent smells are cyclohexane (pleasant, subtly terpenic) and TBME (not-quite-subtle, minty and camphoraceous). But the tastes vary, I know people that run for cover if I mention running a column in TBME. I personaly dislike toluene though - but benzene is fine with me.

One absolutely horrid solvent smell is n-octanol: oily rotten orange mixed with cheap detergent. It is pretty non-volatile so if you work with octanol, it tends to stick with you for awhile.

Also I once run some reactions in neat pivalic acid; it does ruin your sociability for a day or two...

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11. ZAL on February 19, 2007 6:37 AM writes...

I agree with Milkshake, TBME (or MTBE?) smells very good, but I know it has not a good reputation, is that true?
Can't stand Pyridine and AcOH

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12. Thomas McEntee on February 19, 2007 6:55 AM writes...

Speaking of "closet huffers", back in the mid- to late-1970s, some of our plant workers just _loved_ the effects of a warm cloud of toluene or xylene wafting out of the manhole of a 2000-gal reactor. As for myself, I always thought that the smell of chloroform and methylene chloride were tops, with toluene and pentane close to the top.

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13. milkshake on February 19, 2007 7:30 AM writes...

Heptane is not that bad either - little fruity touch it has.

Reactor huffing - in Czechoslovakia workers in a pharma company liked the filtration of one intermediate from warm ethanol - they would always take a break and sit around when the hot ethanolic sludge was poured...

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14. Derek Lowe on February 19, 2007 8:49 AM writes...

I don't mind the smell of toluene, but I don't rank it very highly, either. Chloroform and carbon tetrachloride aren't bad, though - I like then more than methylene chloride, and it's interesting to smell the similarities and differences between them.

As for Lou in comment #7 above, the only way I could recommend n-butanol would be in comparison to something like TMEDA. Maybe in dilute aqueous solution it's more tolerable?

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15. Petros on February 19, 2007 9:09 AM writes...

Chloroform is alright in small doses but very nauseating in larger doses.

I rememmber once doing a series of chloroform extractions in a short placement and feeling quite sick, as well as drowsy, afterwards.

I always though ether pleasant, but less so than e.g. ethyl acetate.

And my nose became pretty insensitive to pyridine through routine use of it.

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16. Liberal Chemist on February 19, 2007 9:33 AM writes...

I worked in a research lab in Durham, England for a while with a visiting faculty member from Czechoslovakia. He mentioned that his home chemistry department used to have solvent / organic identification contests by smell alone. He said he had won one of them by correctly identifying 32 of 40. What he mentioned is that we often recognize the smell but can get confused as to the identity. It is sort of like the Pepsi challenge.

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17. Anonymous on February 19, 2007 9:39 AM writes...

I agree that 4-carbon compounds are bad; the worst smelling thing for me is 2,3-butanedione.

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18. Chemist of Sorts on February 19, 2007 9:43 AM writes...

What about isopropyl ether? Definitely one of my favorites... very nice subtle sweet smell.

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19. MiddleO'Nowhere on February 19, 2007 9:47 AM writes...

I'd have to agree with the first commenter about acetonitrile's smell being corn like, although it smells more like Frito's corn chips to me than popcorn. We had a guy trying to figure out why the SDS wasn't flowing more quickly. He decided to systematically take apart the system (end to beginning) and test it at each step by flowing solvent through it and comparing the flow rate. He created an acetonitrile "fountain" which caused that section of lab to reek like corn chips for several days. Made me hungry every time I walked past there.

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20. JSinger on February 19, 2007 10:14 AM writes...

...toluene or xylene...

My two favorites, as well. Neither is very good for you, though.

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21. Pfizero Hero Doctor (PHD) on February 19, 2007 10:22 AM writes...

C5H5N! Pyridine, I remember it well. Back in the early 1980s while working on the Larvin project in Woodbine, Gerogia, pyridine was used as a process solvent. Combine this nasty solvent with Lannate (a methylthio derivative), methanol and sulfur dichloride, it was a witch's brew. Once exposed the odor lingered for days on one's breath.

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22. CET on February 19, 2007 10:22 AM writes...

Re: Toluene

I like the smell, but I'm pretty sure that's an association thing. I was big into model planes as a lad. Toluene is the major smell in modelling glue. And boy was I glad to hear that the stuff gets metabolized to benzoic acid rather than broken down the same way that benzene is . . .


How much do you all worry about solvent exposure? It seems like the common carcinogens (chlorinated methanes and benzene especially) are more likely to give the lot of us cancer than any of the exotics (HMPA, Me2SO4, etc).

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23. pc on February 19, 2007 10:37 AM writes...

If I have to nominate the most unpleasant one in terms of smell I'd go for pyidine. I also heard that too much of pyridine exposure has the effect of killing sperms, as compared to other solvents. Is that true?

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24. Tom on February 19, 2007 10:49 AM writes...

I used to get concerned about solvent exposure, however, the majority of folks have told me that there is a finite risk associated with using any organic solvent or reagent. Although one can never get it totally down to zero, it can be minimized through respecting the chemicals and exercising some good lab technique.

That makes sense, I feel. Even the more benign solvents aren't all that healthy if you bathe yourself in them and breathe them in at every interval you can.

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25. 3rd year on February 19, 2007 11:24 AM writes...

I don't mind acetic acid in small doses - although I used to work in a chemical plant and had to walk around a large spill - that was a bummer. I also used to work with a waste stream in acetic acid where I tried to make the methyl esters of a bunch of by-products of the reaction to make separation easier. That mix had a very nice fruity smell.

I HATE styrene and pyridine - we use large volumes of both in our current lab. I don't mind acetonitrile, but I haven't noticed the corn smell.

Ethanol is also my favorite, I think it goes back to undergrad when my unknown compound was o-vanillin and I was recrystallizing that in EtoH. Lovely smell.

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26. Pfizero Hero Doctor (PHD) on February 19, 2007 11:29 AM writes...

pc, I heard the same unfounded rumor too. I had very heavy and repeated exposure to pyridine. But I did have a child two years after working with tons of pyridine. So, if the sperm reduction were true it must have been reversible.

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27. Chemgeek on February 19, 2007 12:31 PM writes...

I HATE pentane. I don't know why. Hexane doesn't bother me. Pyridine really turns my stomach too.

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28. Reluctant Chemist on February 19, 2007 12:56 PM writes...

If you like the smell of garlic, try some DMSO...

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29. Reluctant Chemist on February 19, 2007 1:00 PM writes...

I hate the smell of zylene - smells like you've opened a can of Sharpie markers.

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30. Reluctant Chemist on February 19, 2007 1:01 PM writes...

I hate the smell of xylene - smells like you've opened a can of Sharpie markers.

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31. syregnask on February 19, 2007 2:38 PM writes...

Personally I quite like the smell of trimethyl orhtoformate. Fruite, fresh, not too pungent.

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32. Chrispy on February 19, 2007 3:20 PM writes...

On a related note,

How many old-time chemists do you know who still really have much of a sense of smell? It seems to be an common casualty of the job...

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33. Badger on February 19, 2007 3:56 PM writes...

Give me ethylene oxide any day.... ahhh... the smell of fresh cut fields of hay... what great memories ;)

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34. Barney on February 19, 2007 5:03 PM writes...

I recall methyl ethyl ketone having a not-unpleasant odor reminiscent of cheap scotch, but it has been a few years since I last sniffed it.

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35. L. C. on February 19, 2007 5:09 PM writes...


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36. Processator on February 19, 2007 8:52 PM writes...

New Jersey tap water! Oh man!That is a lovely smell. Now being serious, EtOH is awesome and diethylether is kind of addictive.

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37. Bill Tozier on February 19, 2007 8:56 PM writes...

It's been 20 years, but I still can recall the whiffs of octanol and chloroform, from the days of DNA extraction. And now and then a bit of phenol--just a whiff--wasn't amiss.

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38. kiwi on February 19, 2007 9:18 PM writes...

triethyl phosphite has a nice aromatic/gin-like smell to it

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39. BCP on February 19, 2007 10:21 PM writes...

Another vote for TBME, I also have a soft spot for MIBK.

For the bad boy list -- pyridine for sure, and acrylic acid and several of its esters (it's been a few years since I had that pleasure)

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40. Reluctant Chemist on February 19, 2007 10:25 PM writes...

MTBE...ewwwwww...(reminds me of how my local gas station used to smell...)

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41. Fred on February 19, 2007 11:42 PM writes...

Connoiseurs of fine solvents. There are echos here of the language used to describe wines.

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42. Ben on February 20, 2007 12:16 AM writes...

Can't beat's always my favorite. Now, pyridine, however, is every nasty odor all wrapped up into one.

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43. Jon on February 20, 2007 2:04 AM writes...

Mixtures of acetic acid and methanol smell disturbingly of cheap balsamic vinegar. I have noticed a smell to acetonitrile. I can't really describe it now, I'll have to gently waft some tomorrow.
Wafting, that brings me back to grade school when a teacher gave a detailed description of the process of wafting and why its such a good idea. To further illustrate his point he then handed a beaker of ammonia with instructions to smell it to a student he noticed wasn't paying attention

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44. Jordan on February 20, 2007 8:54 AM writes...

One that no-one's mentioned: MEK (2-butanone). At first it has a somewhat pleasant, sweet smell... but after a while it tends to turn nasty. I was always perplexed by this. Useful solvent for the Williamson ether synthesis, though.

Also, I was taught that a lot of what we perceive as the smell of ethanol is in fact due to traces of acetaldehyde -- the origin of the "fruity" or "apple-y" smell of ethanol. True or not?

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45. CR on February 20, 2007 9:07 AM writes...

I'd have to vote for toluene as well...mmm...toluene. The worst for me is benzyl bromide.

Much like Jalfrezi above, only slightly different, I was working at Sigma-Aldrich back in the early '90s and there was a huge pyridine spill. Smelled so bad, and part of the neighborhood near the site had to be evacuated. Not many people volunteered to clean it up---especially the males.

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46. Aman on February 20, 2007 11:03 AM writes...

my lab-mate uses ethanethiol..
and man does it smell...a wee bit fills up the room...even when he handles it in the hood..

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47. Jason on February 20, 2007 5:08 PM writes...

This place has great odor descriptions of many chemicals, including ones discussed here. Just taking the first one on their list for example:


odor type : ethereal
odor strength : High , recommend smelling in a 1.00 % solution or less
odor description : ether green nut earthy sweet vegetable
substantivity :

Used in :
tropical fruit

Natural occurrence :
citrus fruits

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48. TMS on February 20, 2007 8:00 PM writes...

I am kind of surprised you never mentioned methyl-t-butyl ether (MTBE) which is so prevalent in European labs like the one you once inhabited in Dortmund.


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49. Yttrai on February 21, 2007 8:38 AM writes...

The genetics of smell, and how they relate to our everyday lives. How awesome. For me:

Ethyl acetate = YUCK
Hexanes = Yum.
Benzene = Yum.
Tolunen = Yum.
Ether = Yum.
nButantol = Yum - am i the only one?
Methylene chloride = HOLY YUCK.
Chloroform = Yuck.
TBME = No opinion.
THF = No opinion.
Pet Ether = No opinion.

And DMF, DMSO, and MeCN are invisible to me, except for the contaminants. Not enough experience with anything else to pass judgement. My least favourite smell in the lab ever is definitely piperidine.

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50. TNM on February 23, 2007 3:55 PM writes...

I second piperidine! Oh that horrible spermlike smell...

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51. richard blaine on February 28, 2007 9:30 PM writes...

In the building where I work, chemists' offices are adjacent to the labs, so you can always tell when your labmate is into some stinky stuff. This can work in your favor, however.

Recently, I was enduring yet another in a series of unannounced visits from our boss when my labmate opened up a bottle of thiophenol in his hood. The smell quickly pervaded the office, offending the sensitivities of the boss to the point that he began to feel nauseated. (Experienced chemists will have surmised correctly that our boss hasn't worked in a lab for 25 years.) He beat a hastely retreat, much to my relief. Afterwards, I taped over the Aldrich label on the thiophenol with one that read "Boss Repellant." Also, I made a pact with my labmate that whenever the boss was in one of our offices and the conversation was getting uncomfortable, a secret signal would be given and the other would open up the thiophenol to drive the blighter off.

Even compared to other Ar-SH, thiophenol is truly awful. Another class of compounds whose smell I find disgusting is acid chlorides, in particular methacryloyl chloride.

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52. Dr. Daniel Gironés on March 5, 2007 10:26 AM writes...

I recommend to all of you to have a good ventilation system and stop smelling most of the solvents you mentioned. Just for the sake of your health.

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53. Anonymous on April 30, 2007 11:22 PM writes...

To me, THF smells like urine, Ethyl acetate has not even a hint of fruityness, methylene chloride has no odor until it begins to irritate my nasal mucosa, I have yet to notice any odor of chloroform, TBME smells floral, and lab ethanol smells *exactly* like acetaldehyde. Ether smells like ether, hexanes smell like not much as do pentanes. Oh, from what I have read, the toxicity of hexane metabolites is totally reversible. Petroleum ether smells like gasoline.
Enol ethers and esters all smell the same, sort of cedary.
Tert butyl isocyanide smells odd, but not bad.
Smells are wonderfully idiosyncratic.

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54. venkat on February 10, 2010 9:24 AM writes...

how decrease the smell of toluene.

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55. Max on March 1, 2011 8:16 PM writes...

I must say ethanol does have a very nice sweet smell to it. I tend to find ethyl acetate smells like acetic acid. Maybe ours is off.

Thiophenol is rather nasty and does smell like burnt ass.

One chemical I truly hate is 2-Iodophenol. The smells sticks to your clothes for weeks after using it.

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56. Vrunda Sheth on April 13, 2011 2:06 PM writes...

My fav: Toluene and MEk.. ahhhh love the smell of it...but It gives awful headaches...

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57. Neil on January 5, 2012 1:42 PM writes...

Pyridine is the most terrible and horrible thing to smell. I once used it outside the fumehood and had was to vacate the lab!

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58. Neil on January 5, 2012 1:45 PM writes...

Pyridine is the most terrible and horrible thing to smell. I once used it outside the fumehood and had was to vacate the lab!

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59. Neil on January 5, 2012 1:54 PM writes...

Pyridine is the most terrible and horrible thing to smell. I once used it outside the fumehood and had was to vacate the lab!

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60. Lee on February 26, 2012 6:14 PM writes...

As an undergrad, I once filled up the chem building with methyl vinyl ketone (MVK, a highly toxic alkylating agent and strong lachrymator) prepping for a Diels-Alder rxn to produce oxygen heterocycles. That was pretty nasty.

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61. Lee on February 26, 2012 6:42 PM writes...

Senior grad students and lab personnel commonly used their nose to detect the presence of organic solvents to indicate the completion of rotovapping. I often wondered how common this practice was at other academic institutions and industrial labs.

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