Trotsky
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Microwave Assisted Nitrations
I was wondering if anyone here has any experience with microwave assisted synthesis, particularly microwave assisted nitrations?
I was attempting a nitration of cellulose, the salt used being NH4NO3. However, I did not realize that my H2SO4 was 34%, but when I made the bath and
there was no heat generated I knew something was up. that's when I realized my mistake and sought a method to rectify it.
Figuring it couldn't hurt, I microwaved the solution in 15 second bursts, allowing it to cool between bursts. This was done in about a 5 minute
period (it didn't cool completely, of course, but enough to handle the beaker without gloves.
A white misty fume was emitted each time.
I allowed it to cool naturally and then placed it in an ice bath when the danger of shattering the beaker was gone.
Mixture was cooled to 2C.
It was then removed and placed on a shelf in a dark room.
After two hours I came back to check it.
The room was at 21C, but the liquid had warmed to about 38C.
I placed this back into a cooling bath and I'm waiting now. Given that nitration conditions weren't optimum, I'm going to let it sit overnight, but
I'm somewhat hopeful now.
Would you assume that this is likely heat generated by nitration or some other reaction?
I'll follow up tommorow when I've cleaned and neutralized the cotton.
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AndersHoveland
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If concentrated nitric acid is left in contact with organic matter for too long, it can gradually oxidize it. This is typically why the reaction time
of nitrations is kept to a minimum (at least for sugar alcohols).
In the case of cellulose, I would guess that some of the cellulose was slowly hydrolyzed and brocken down under the acidic conditions. As soon as the
aldehyde moiety is freed, it would be immediately oxidized to a carboxyl group (and possibly opening up the rest of the molecule to further oxidation
through tautomerization).
I am surprised you did not observe any brown fumes, though your acid was probably just not concentrated enough for this to happen.
[Edited on 5-3-2013 by AndersHoveland]
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Trotsky
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After 12 hours... nothing. Cotton feels exactly like cotton and burns just like cotton too. I wonder what caused the heating given that the
cellulose doesn't appear to have been altered. Well, if it was, whatever happened didn't alter the physical properties significantly.
Cotton was cleaned and neutralized. And nothing happened. 
Fortunately it was a small attempt.
I wonder how much benefit microwaves would be in a nitration with stronger acid. Maybe it could drop reaction times, I dunno. It was worth a shot
given the probable failure.
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