Friday, October 4, 2013

New Balloons

Although I have long believed balloons to be mostly ineffective (in a laboratory setting), sometimes I use them for the placebo effect. In fact, I've made the following claims to our lab: 

1. Balloons are permeable to O2!  
Source - Knowledge accrued through chemistry - Ni(0). 

 2. Balloons are not permeable to moisture!  
Source - Knowledge accrued through chemistry.  

3. How do I really be air free in the lab? 
-Degassing by argon sparging (15m) or freeze pump thaw? I've never seen a real difference here... the rumor is freeze-pump-thaw is more effective... (but sparging worked fine for Ni(0).) 
-The solvent system solvents are oxygen free. I used to pull fresh ether straight from the solvent system and wash my Ni(cod)2. 
-Schlenk flasks and use proper shlenk technique 
-Use the golvebox 

4. Remember, most of what we (BaranLab) do isn't that O2 sensitive, so don't worry too much. (However, we do a lot that needs to be water free!) 

5. But Dane, you've got 3 balloons in your hood right now! 
-yes, I know, they make me feel emotionally stable; we stir our homogenous reactions too, which is also unnecessary.

 It is with all this in mind that I say: these new balloons are sweet as hell.
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8 comments:

  1. Alexander IrvineOctober 5, 2013 at 9:51 AM

    I imagine there must be some way to obtain a balloon made of a material that would prevent O_2 from entering the system. A standard balloon could perhaps be sprayed down with some sort of inert resin or silicon grease that would at the very least make O_2 entering the balloon a non-issue. Ask a fellow material chemist and see what they have to say. I bet they would find this an interesting challenge.

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  2. DaneOctober 5, 2013 at 10:37 AM

    You're probably right, I suspect there is some hypothetical covering, but is it worth it? Schlenk equipment is pretty expensive - although, once you have it, its a sunk cost and easy to use.

    I guess I should mention that balloons (in my experience) aren't immediately permeable to oxygen. I backfill reactions with argon from a fresh, double balloon with no issue. However, on multiple occasions I left balloons in Ni(0) reactions overnight, only to have the nickel oxidized by morning; so there is an equilibrium across the balloon. (I guess I should note that this is all observational, I never did all of the proper controls to prove it was O2, however, I've heard others echo this opinion independently of mine, notably Dave Collum.)

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  3. milkshakeOctober 6, 2013 at 7:08 PM

    1) doubling the balloons (balloon within a balloon) not only saves the reaction but also helps to prevent hydrogenation-related fire, should one of the balloons rupture in the middle of the night. I suppose this doubling also slows down the oxygen penetration by a factor of 2
    2) balloon - assisted sparge of reaction mix works best with Ar rather than N2 because it blankets better, with buzzing the flask on ultrasonic bath, with two needles through the septa - this is fast (5-10 min) but adequate for most Pd-catalyzed couplings
    3) since hydrogen is extremely leaky, for large-scale hydrogenation it is better not to use the needle-through septa balloon hookup but use a 3-way stopcock with a joint at the bottom, and replace the H2 balloons daily

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  4. AnonymousOctober 30, 2013 at 12:22 PM

    Balloons are also my black magic ritual for air-free conditions.

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  5. UnknownNovember 20, 2013 at 5:26 PM

    Yeah, so why can't we get over stirring heterogenous reactions? I learned early on in undergrad PChem that stirring heterogenous mixtures is pointless because diffusion is so fast. What is this psychological need to stir them? Theoretically, the stirbar could be a source of contamination.

    I vow to do my heterogenous reactions without stirbar from now on.

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    Replies
    1. DaneNovember 20, 2013 at 6:55 PM

      I can think of a few reasons to still stir them that aren't psychological...
      1. Heat transfer (in particular for large reactions), keeping them at exactly the temperature you want
      2. If it becomes heterogeneous while you're not watching (product crashes out)

      But yea... you shouldn't have to... maybe I'll stop too.

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    2. milkshakeNovember 24, 2013 at 9:38 PM

      Diffusion is fast enough maybe in gases at normal pressure, but not quite so in slightly viscous liquids. In reality if you don't stir your reaction you will get concentration gradients, with heavier stuff or more concentrated stuff sitting on the bottom or floating at the top. Newly-formed predicipitate can deposit over your (poorly-soluble) starting material as a poorly permeable gummy layer and make it unavailable. So whatever you learned in freshman calls is worth crap if you don't employ common sense - for example, what happens when you put few sugars into your coffee and then you drink it without stirring it first

      Delete
  6. openmindMarch 9, 2014 at 5:59 AM

    when you make inert balloon, you probably not do 3 times vacuo-inert steps, so when you get a inert balloon, it must with a little atmosphere, and the trace oxygen will damage your reaction esp. micro-scale reaction.

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