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Old Jun 25th 2016, 10:13 AM   #1
gggabimandl
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URGENT: purification of azobenzene-modified polyacrylic acid

Hello! I am an undergraduate chemistry student working on my Honors project, and I am in way over my head. I am extremely grateful for any suggestions. I have already spoken to grad students in my department, and now I am just super desperate and coming to the internet for help.

I am currently working on a DCC coupling of 2-(4-phenylazophenoxy)ethanol with Polyacrylic acid (MW 130,000) and I have been having trouble for months (I've done this synthesis 20+ times). I finally decided to try adding DMAP as a catalyst to aid in the esterification process, which appears to work when I do a TLC (silica TLC with toluene/HOAc), but I can't isolate my product! Previously, without using DMAP, the TLC would show the azobenzene separating from the PAA. So now that they are not separating, I am confident that the coupling appeared to work.

Reaction mixture: DCC, DMAP, 2-(4-phenylazophenoxy)ethanol and PAA, dissolved in NMP.

The protocol i am using (An Azobenzene-based Light Responsive Hydrogel by J. Fraser Stoddart et al. if you wanna look it up) is totally useless, it seems. Their workup says to add NaOH to neutralize (my solution is at 7.5 already...) and filter the precipitate and wash with MeOH and NMP and then dissolve in water and precipitate in MeOH. I actually emailed them because this totally does not work, and they said just to see if I could wash the precipitate with methanol and leave it at that.

So far, i have tried the following to isolate my product:
- Adding NaOH until pH = 9, i get a sticky orange precipitate (which is good!) and then I vacuum filter the precipitate and wash with methanol. I end up with a hard, dark brown disgusting looking thingy.
- Adding NaOH and methanol and centrifuging, again I got a dark brown ugly looking thing, but in -very- low yield.
- Pipetting the mixture into hexanes (since PAA is insoluble in hexanes) and centrifuging. I again got a dark brown thingy, which I am currently vacuum drying, rather than rotovaping because someone told me to stop rotovaping it.

Any suggestions to properly purify this stuff? I feel like im just destroying my product, which I have precious little of.

Thank you!
Gabi
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