Org Prep Daily

December 2, 2009

Predetermined conclusions

Filed under: Uncategorized — milkshake @ 6:56 am

In the last year of elementary school I got encouraged to take part in the science fair – The top winners of the national highschool science project competition could possibly earn the admission to a college of their choosing. I was a new chemistry club member and it was decided there that I ought to try an analytical chemistry project –  an assay to determine content of vitamin C in various foods by titration. There is a simple redox method and I could compare how the processing and contact with metals diminished the ascorbic acid content. (Cooked food has less ascorbic acid because it gets oxidized and metals catalyze the oxidation etc. etc.)

So I started on this stuff but it bothered me a bit when I was reading in the book that described this analytical method that there are actually other components  in the food that also have reducing properties and they would show up in this titration and I had no way of telling them apart from ascorbic acid or figuring out their relative ratio – so my result would always end up higher, as a sum of two unknown values. The club boss suggested that I should not dwell on this over too much –  after all, it was an established method and I was only doing a modest experimental work to practice for more serious research – and that I ought to get on with the work for which she had the plan laid out for me. So I listened and did the whole thing.

Next, before I even completed writing up the ascorbic acid stuff – and since we were working so well together – the chemistry club boss suggested that the second project I should try is to measure lead in fruit picked from trees growing along the roads because of the health issues posed by the wide-spread use of leaded gasoline at that time. There is dithizone, a ligand that makes a deep purple complex with lead and she had a spectrophotometer in the lab which she wanted to put to some use and it would be much more interesting project – one that had a chance of winning awards for our club…

A small problem arose when I finished the calibration curves for the dithizone-lead complex standards and proceeded to apples picked from trees along a busy road:  it turned out that there was not much lead in those apples (I could barely detect a hint of the colored complex but there was no way to quantify that on this instrument). I got promptly sent out on missive to try to find some more-contaminated fruit so that we can have material to support our serious study –  I was told to make sure to pick the fruit only when there was no rain for few days, and that I should prepare the samples from the surface layer only. (How exactly you separate the surface in a reproducible way was not obvious to me – but reproducibility was apparently not the biggest concern in our project). When I asked if this really was the way to go about the  sample collection, it was made clear to me that I better find some lead-laden fruit somewhere soon or she will not waste her time with me anymore. So I stopped attending that chemistry club and resumed my research on home-made fireworks and rockets and methods for  ethanethiol production – the projects in which I found some encouragement from my non-chemist buddies.

9 Comments »

  1. She sounds like the folks at the Climatic Research Unit.

    Comment by Chemgeek — December 2, 2009 @ 10:40 am

  2. I suppose once you know what the data ought to be the main question is what is to be done to get them so that you can win the science fair or whatever (and no-one needs to find out). You won’t even pause the second time as you become entitled to defending your deserved success by these necessary means.

    Btw, I used to count myself as a enviro-movement fan before I realized what passes for an independent expert in the field

    Comment by milkshake — December 2, 2009 @ 11:59 am

  3. Very politic of you mate. I could understand if a few more swear words and insults were added to that post. Sometimes the academic (child) inside all of us just wants to prove themselves right and then stop at nothing till they do.

    Comment by OrganicOverdose — December 2, 2009 @ 7:43 pm

  4. There’s a couple of lessons here; we respond to incentives. She had no incentive to make your project reproducible, since her goal was to win the science fair, and they don’t care about reproducibility at the science fair. You, on the other hand, wanted validation, and you could get that from your non-science buddies by blowing stuff the hell up. Not surprising that you went that route. Good thing, too, because if you had gone the other way you might be a stodgy analytical chemist rather than the internet-based purveyor of organic awesomeness that you are today.

    Okay, I have a threadjack question too. I have a labmate who needs to add a methyl group to a methyl alkyl ketone in a mild manner to produce the related tertiary alcohol. In other words, she needs to do the equivalent of adding methyl Grignard to a ketone, but Grignards and methyllithium are incompatible with her molecule. Does anyone know a mild, reliable procedure for this reaction? Sci-finder yields a crapload of “put in MeMgBr” procedures and a few sketchy-looking thallium or selenium things.

    Comment by opsomath — December 4, 2009 @ 1:51 pm

    • This is a dumb idea, but olefinate (Tebbe?) and hydroborate?

      Comment by Chemjobber — December 4, 2009 @ 1:57 pm

      • hydroboration won’t do, you would need Markovnikov hydratation – not nice on tertiary alcohol…

        I don’t have much experience (Krest17 here is the person to go to) but for your scenario the best would be to use organocerium MeCeCl2. You can buy anhydrous CeCl3 beads in ampoule, dry some LiCl on highvac in vacuo, mix CeCl3 with two equivs of anh LiCl in anh THF, stir overnight in the presence of activated powdered 4A or 3A sieves and let settle and you got CeCl3.2LiCl solution that is great for this kind of sensitive ketone addition stuff when combined with Me-Grignard or MeLi. Check out publication from Knochel and Krasovsky in Angewandte about two years back.

        Also you can try Me3Al, it is available in 1M toluene solution (pretty air sensitive but I never had fire with it, it adds to ketones and tolerates amides, esters)

        Comment by milkshake — December 4, 2009 @ 4:19 pm

      • You know, if I could talk her into backing up a couple of steps, this might work. Put on an allylmethyl group instead of the ketone, and just do a Markovnikov hydration like Milkshake-sensei says down there. (Oxymercuration-demercuration?)

        Oddly, I’ve never had to do a simple add-water-to-a-double-bond reaction before. You learn about it in sophomore organic chemistry, which probably means it doesn’t work.

        Comment by opsomath — December 4, 2009 @ 5:17 pm

    • See, I told you it was a dumb idea! :-)

      Comment by Chemjobber — December 5, 2009 @ 2:28 am

  5. I agree, a simple hydration is not very promising. However there is a nice Mukaiyama hydration of trisubstituted alkenes with Co(acac)2/PhSiH3/O2. See e.g.
    Synthesis of (+)-Cortistatin A
    http://dx.doi.org/10.1021/ja8023466

    Comment by Alexey — December 4, 2009 @ 7:49 pm


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