Octobergeekfest
October 1st, 2009 by LiqCIn the spirit of the near-Nobel worldwide procrastination peak, I’d like to try something new.
The readership of this blog spans all areas of our beloved and increasingly ill-defined subject. While our knowledge may have significant overlaps, there’s always someone who has more expertise in something you’re interested in. Usually you’d walk across the hall to a colleague of yours, but this option is not always available. Besides, we all harbor all sorts of obscure knowledge that we picked up god knows where and that will die with us. Unless we blog about it.
Irony aside, I would like to invite you to do either of the two things:
1. Identify a chemistry-related topic that you feel most comfortable talking about to share your tricks of the trade. It’s quite hard to do, I can’t think of anything unique enough that I’m particularly good at myself. But I’m sure there are people who can. Plus, the lab lore includes not only understanding of what’s going on in your flasks.
2. Ask a question that perhaps has been bothering you for the longest time and you have not been able to find an answer. This is not for Scifinder/Wikipedia/LMGTFY kind of questions. Please don’t be too phylosophical, as in “why are people so stupid?” If you feel really like it, though, go nuts.
Don’t be shy. Embrace your inner geek.
Here’s what puzzles me: why do amines turn yellow on storage? My first guess would be aerial oxidation to imines, followed by formation of Schiff bases and all sorts of aldol-type oligomerization to form some chromophore. The color does not appear out of anywhere, right? If it’s the case, is there a way to prevent it? How about radical inhibitors, which are a must in things like polymerizable olefins? Aromatic amines don’t have alpha-protons, but they sure do go down the yellow-orange-brown-black road as well. Something quinoid?
Looking at an old stockroom is a nice reminder that we all are thermodynamically unfavorable. This too shall pass…
I always had the sort-of-layman’s notion that being actively thermodynamically unfavorable was a fair start on the definition of “living”. Unfortunately, deep thoughts on the meaning of life do little to answer the question of why amines turn yellow!
So the reason for yellowing amines isn’t known? I would think this would have been figured out by now.
Here’s a stupid question:
Has anyone ever tried to characterize the crud that’s in a yellow bottle of amines?
There is a patent that claims to prevent discoloring of amines by adding ethylenediamine during distillation
but there is not a good explanation given about why discoloration happens except “This is usually attributable to unknown impurities which form over time.”
Rats! — dropped the link:
One more time (I’ll blame it on jet lag after a trip to Japan):
color stabilization of amines
you’re welcome.
Thanks!
http://www.patentstorm.us/patents/7169268/description.html
Amine + O2 gives fast charge transfer complex then oxidative degradation. The champ is N,N-dimethylaniline – aspirator distills white, break the seal, yellow! Pump down, white. Wait and pump down… screwed. NVP monomer vac distilled then never exposed to oxygen radiation surface grafts like a champ. Any exposure to oxygen gives you high graft solution viscosities afterward and crappy saline contact angles.
The JACS article was on NMP. In theory, everybody in the place read it. In practice, only one chemist got a write-down for embarrassing process engineering – knocked 10 degrees off the contact angle and an hour off device washing without a single multivariant optimization protocol being calculated, run, and reported as a PowerPoint presentation. It simply worked.
Aerial oxidation to imines? I’m stymied. I always thought the amines went ‘yellow’ because of the hydroxylamine -> nitroso -> nitro transformations.
Why does DMF go red when you heat it hard with base?
How come P(triple bond)CtBu goes yellow over time but according to all analysis is unchanged?
Do you think that wearing dirndl would make your lazy reactions run faster?
Should nucleophiles be required to take their medications as a condition for their release?
It is a fact now that yelling at your reaction really hard can change its outcome. Now the influenced of phases of Moon and tidal forces needs to be studied. Also, it would be nice to know what to yell. I’m sure that on proper mechanoacoustic agitation Pd will acquire special properties at midnight on equinox.
My results indicate that Grignard reactions work best under the waxing crescent. However I don’t have any data for new, first quarter, full and third quarter. The results indicate the reactions are only affected by the moon; the suggestion that the sun can affect reactions is nonsense.
What is the brown stuff in Aldrich Pd(PPh3)4?
Oxidation products certainly, but more specifically…
Pd black, phosphine oxide?
phosphine oxide? are you kidding?
I don’t know. What else?
Pd(II) oxide and hydroxide are dirt-brown. A sign the Pd(0) had had enough of this silly low-valency catalyst business and has gone onto other things, such as daisy-pushing
Can’t Pd(II) oxidize phosphines?
Not without a co-oxidant (ie, an oxygen source). Pd(OAc)2 reduction to Pd(0) via oxidation of phosphine to phosphine oxide is sometimes implicated, but not always.
To LiqC – The question was about color, even in P(O)Ph3 formed, which is possible, – it is white solid.
Pd(II) oxidizes phosphines (and also triethylamine) but at elevated temp
or just add water
OL 2008, 3505 Buchwald
Here’s a trippy: Acrylamide monomer dissolves in lots of monomers. Polyacrylamide dissolves in mostly nothing but water. Slowly copolymerize acrylamide with other stuff in a vacuum ampoule. Polyaycrylamide microprecipitates out to go opalescent. Quite pretty. Then it polymerizes some more and goes to crud.
Here is one that none of my grad school profs could provide a good answer. pKa of a proton on a tertiary center (tBuLi) is higher than that of a methyl group(nBuLi). Why doesn’t a bottle of tBuLi convert itself to a solution of Me2CHCH2Li ?
Good one.
I’d say your answer is “kinetics”. It’s already an anion, and thus making isoBuLi will have to involve a dianion. Even if you consider an old tBuLi bottle, which contains some isobutane and lithium oxide/hydroxide, you can’t just deprotonate unactivated alkanes, especially in hydrocarbon solvents. This process is extremely slow. This is why simple organolithiums are normally prepared by redox reactions.
Basically, for the same reason your tBuLi in pentane does not become pentyl lithium.
I agree with LiquidC. also, I’ll add that concerted anion rearrangement like tBuLi to Me2CHCH2Li is forbidden by Woodward-Hoffmann rules, so it’d have to rearrange by some other method, which would require breaking the aggregates that form in solutions of alkyllithiums.
It’s Corey-Woodward-Hoffmann rules.