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Folks,
For a lab unit on Schlenk line and glovebox techniques, I have been using manipulations of reduced CpZnCl2 in solution, which gives nice color changes upon exposure to oxygen, followed by synthesis of diacetochromium(II) hydrate as described in the classic text by Jolly (Jolly, William L. The Synthesis and Characterization of Inorganic Compounds, Waveland Press, 1991, pp 442-444). I am looking for a replacement for the chromium complex synthesis. I like this synthesis because it can be completed in one 4-hour lab period, it is conveniently oxygen- but not water-sensitive (so it is a little more forgiving), and it quickly shows nice color changes if exposed to oxygen at various points. My main concern is the fact that if the synthesis 'goes bad' because of air exposure, the resulting product *badly* mucks up the Schlenk filter tubes, giving material that not only does not filter but also takes several rounds of harsh oxidants to clean off. I would also like to move from chromium to a less toxic metal, if possible. Does anyone have any suggestions of syntheses they like for teaching air-sensitive techniques? I am not seeing anything in any of the usual texts (Woolins, Angelici, Szafran) that fits well.
Thanks.
- Joe
I don't have a great suggestion. I have always wanted to use reduced Cp2ZrCl2 (I think you mean Zr?) as a colormetric indicator of student ability as an end-of-term practical exam slash audition to work in my laboratory.
Most of the air and water sensitive things we do in our teaching lab are more accurately described as "air" and "water" "sensitive," because we have a hard enough time getting products anyway. I'll be following this thread to see if anyone has a good suggestion!
Adam
I have students prepare Ferricenium BF4 via Schlenk line. This reaction involves ferrocene plus AgBF4 and generates Ag metal as a biproduct. Though I don't think you have to make ferrocenium on a schlenk line, I use this procedure for a number of reasons:
1. As others have suggested, while in solution it is somewhat air sensitive but a beginning student can still get pure product in good yield. However, you can also use a cannula to transfer some solution to an open beaker and see it "go bad" pretty quickly;.
2. It involves pretty much all of the common Schlenk techniques--transfer of solutions, filtration to remove Ag, filtration to collect product, etc.
3. It is aesthetically pleasing, since the orange color of ferrocene becomes immediately blue. Interestingly, depending on how you view the solution (or the solid) with a flashlight, the color appears to be either blue or violet! Also, when you add ether to precipitate the product, you get excellent microcrystals that form rather than just a powder!
4. I also chose this synthesis because the product is paramagnetic and I was looking for a mag suseptibility lab as well.
The main "downside" to this expt is that it does generate Ag metal which can form a film on glassware which requires cleaning. Also, I use diatomaceous earth to help catch the Ag when filtering so it doesn't get caught in the filter pores. This requires the filter aid to be present when degassing, and sometimes students will not be open the stopcock to vacuum slowly enough when degassing the apparatus. They can then cause some filter aid to get up in the Schlenk manifold.
If anyone is interested in the procedure I'd be glad to send my lab handout to you. You can get ahold of me at bjohnson@csbsju.edu.
Brian
Brian-
You could consider using HBF4 or FeCl3 instead of the silver salt. The preps are detailed at the end of the classic Connelly and Geiger paper (Chem. Rev. 1996, 96, 877 DOI: 10.1021/cr940053x http://pubs.acs.org/doi/pdf/10.1021/cr940053x). The FeCl3 prep still gives you all the features you were looking for without having the Ag (s) to deal with. Just a thought.
There was a typo in my initial post. The oxygen indicator is Cp2TiCl2 reduced with Zn. I use a toluene solution ("green juice") as an indicator in my glove boxes and an acetonitrile solution ("blue juice") for the Schlenk line practice.
Hello, Joseph.
If you are still looking, I (humbly) recommend a J. Chem. Educ. article I published seven years ago (see below). My research group was preparing air-stable THF complexes under anaerobic conditions to react with an air-sensitive reactant. I noticed that our procedure involved all the common Schlenk techniques, so I developed a lab exercise for my classes. The one downside is that all the starting materials and products are actually air-stable, so there is no "penalty" if a student makes a mistake; on the other hand, the metal source is safe (CuCl2.2H2O).
Craig Davis
Davis, C.M.; Curran, K.A.. “Manipulation of a Schlenk Line: Preparation of Tetrahydrofuran Complexes of Transition-Metal Chlorides.” J. Chem. Educ. 2007, 84, 1822-1823.