Photophobic Chemistry
by azmanam on Mar 09 2010 (12572 Views)
Ugg... what a pain. The reaction I'm doing today produces a low molecular weight, light-sensitive α,β-unsaturated ketone as a product. It's a derivative of methyl vinyl ketone. Not only is it low-boiling, it also polymerizes upon standing in light. Ugg...
Now, I've worked with light-sensitive reagents (like the iodomethane and methallyl iodide) before, so I'm comfortable turning off the light and covering the reaction with foil to keep out extraneous photons. That's not so bad, because when the reaction's done, you can flip on the light to work up the reaction.
Not so when the product is light sensitive. Gotta keep the light off. Gotta extract in the dark. Gotta dry the organic layer with foil around the flask. Gotta rotovap in the dark with foil around the flask. Worst of all, gotta run a column in the dark. For that, I cut off some of the sides of a cardboard box and used them as a shield to block the light and holed myself up in the dark corner of my hood to run the column. Then gotta rotovap the fractions corresponding to product in the dark in foil. Take the mass in the dark... Ugg. Pain all around. Oh yeah, I forgot I gotta keep the NMR samples in the dark while I acquire the spectra, too.
Plus, gotta keep the product away from light until I set up the next reaction (which is going on right now)... and that's gotta be in the dark. At least when this reaction's done, I can turn the lights back on.
Fortunately, the first reaction worked quite well. I ran two multi-gram reactions side by side in the dark and got quantitative yield on both.
So while I run off to find some vitamin D supplements, tell me what the most operationally painful experiment you've set up is. I'm sure many of you have stories that make mine seem trivial. What experiment's the biggest pain to run? I think any reaction involving FOOF (the most awesome, most onomatopoeic molecular formula evah) has to be up there.
you should chat with my poor synthetic collaborators!
http://dx.doi.org/10.1002/cphc.200800581
i mean:
http://dx.doi.org/10.1021/ja802883k
My colleagues used to prepare for their Evans' aldols for what seemed like days; buying the dibutylboron triflate, drying all their solvents and their glassware, preparing elaborate substrates, etc. The reactions themselves seemed to take 12 hours from start to finish -- not too crazy, I suppose, for a key carbon-carbon bond.
I'm guessing that there are far more elaborate preparations out there.
Might be a stupid suggestion ( photochemistry with ambient light is something I've managed to avoid except with one project ) but are there any low energy wavelength bulbs you could swap out in a lamp to keep yourself from knocking things over? I imagine people still sell the red-light bulbs for darkrooms. Probably more trouble than it's worth though.
or, um, work in a lab where all the lights are yellow and there are black blankets over the windows. it only drives you a LITTLE crazy...
I'll also suggest trying darkroom bulbs: Between ebay and the rest of the internet, they can be had for pretty cheap. If you work after dark, then maybe one or two well placed bulbs could make things loads easier for you...
@sam: yeah making photoactivators must be a lot of fun.
@chemjobber: tell your buddies to switch to the crimmins aldol. (http://www.unc.edu/depts/mtcgroup/aldol.html) Milder (and cheaper!) conditions, and the thiazolidinethione is more versatile than oxazolidinone when it comes to auxiliary removal.
If this were going to be a regular occurrence, I'd probably invest in some new lights. But, as it is, it's a one-off event. I did it on test scale a few days ago, and scaled up yesterday. Yesterday's scale up ought to give me enough material that I never need to run that reaction again (famous last words....)
Out of all the synthesis I can choose from, I decide to make compounds that are extremely air and water sensitive. Just pumping the flask would take half an hour. Sometimes I bang my head against the wall for not choose anything that is, perhaps, not sensitive to all things in life.
Hi, everyone
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It can always get worse! At least your product isn't air sensitive, radioactive, and prone to photoinstability.
I recall making some silver compounds that required work under red light. That's ok for the first few hours, then it's maddening. I remember tag-teaming a 36 hour fractional distillation with my partner, babysitting a formylation that took nigh on two days to complete, making my own sulfuric acid, the preparation of cesium... Each had their own challenges, some technical (apparatus), some more with just the nature of the material.
Then again, my idea of retirement is working through Georg Brauer's Handbook of Preparative Inorganic Chemistry. I'm pretty sure FOOF is in there too let alone stinky ClF3