Nectarine
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Nitration of aromatics - order of addition
I've been messing this up for too long. Can someone help me out with this, its simple nitration of aromatic compound.
Specifically I'm working with quinolinone compounds. I like not using a solvent, as I try to be 'green'.
5g of quinolinone are added to a RBF, and cooled in an ice bath. A solution of 1:4 HNO3 (15M)/H2SO4 is cooled to 0C and added portion wise.
I added drop by drop, which created a black, viscous solution on the bottom of the flask. Seeing as the temperature wasn't raised much, I added about
500mL fairly quickly, which resulted in brown NO2 formation in flask. I allowed to cool, and will extract, but every time I see NO2 form, I know my
yield went to shit.
Should I be adding this product to a solution of nitric acid? The other nitro-substitution positions are negligible (5%, from the literature).
I guess my real question here is how long would one plan to set aside to do a nitration of 5 grams of substrate? An hour, by dropwise addition? It
seems awfully slow!
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Metacelsus
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When my organic chemistry class did a nitration reaction, we added the substrate (methyl benzoate in this case) to half the sulfuric acid, then added
a mixture of the nitric acid and the other half of the sulfuric acid. You could try something similar.
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AvBaeyer
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What is the structure of the quinolone that you are trying to nitrate and what is your expected product? Quinolones are relatively deactivated towards
nitration and will not react as readily as quinoline (see, eg, J. Chem. Soc. 1957, p. 2521) and so may not nitrate using your relatively mild
conditions. Do you have a reference for the nitro compound that you are trying to make? If so, how was it made? A bit more information is needed
before help can be provided.
AvB
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Oscilllator
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I'm no expert, but in every nitration I've ever seen the reagent has been added to the nitration mix, especially if the reagent is a solid.
I gather that this is because if the acid is dropped on the reagent, then it will instantly overheat in that spot (often forming black tar as seen
here) whereas when the reagent is dropped into the cold, liquid acids the temperature does not have a chance to rise.
Try adding the quinolinone to the mixed acids, and see if that works. I would be not at all surprised if that produces better results.
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vmelkon
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Quote: Originally posted by Nectarine  |
5g of quinolinone are added to a RBF, and cooled in an ice bath.
Seeing as the temperature wasn't raised much, I added about 500mL fairly quickly,
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5 g and you added 500 mL of acid?
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kmno4
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| Quote: Originally posted by Nectarine | I've been messing this up for too long. Can someone help me out with this, its simple nitration of aromatic compound.
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There are 1001 ways of nitration of aromatics.
If it is simple, you do not need any help. 
A tip: see this article DOI: 10.1007/BF00519820. It is about nitration of some quinolinones.
First - is your quinolinone stable in conc. (80%-96%) H2SO4 ?
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Nectarine
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Sorry, 500uL!
The starting material is 3,4-Dihydro-2(1H)-quinolinone. It should nitrate @ the para-position to the nitrogen, although with heating I'm sure some
di-nitro products are formed.
I can find a few papers that talk about nitration of the compound. All papers vary though;
Some dissolve in Sulfuric acid, and add nitric/sulfuric solution.
Some add the solid to sulfuric/nitric solution.
And still others claim the way I did it - adding the sulfuric/nitric solution to the solid.
Trivial stuff, or what seems to be, yet my yields always suffer. Terribly.
I will attempt again by dissolving in sulfuric acid, 0C, and adding the nitric/sulfuric solution.
One paper that does this:
http://www.sciencedirect.com/science/article/pii/S0960894X08...
"Commercially available 3,4-dihydro-2(1H)-quinolinone was used as a starting material, which was treated with a mixture of concentrated sulfuric acid
and nitric acid (4:1) under ice cooling to give compound 1. T"
Since it is so trivial, its not even in their methods section, which I despise. Did they dissolve the product in sulfuric acid first? Did they cool
the sulfuric/nitric solution before adding? Was temperature maintained? What did the product look like?
It's a medicinal chemistry journal, so I understand, but publishers should really enforce methodology explained more, even if it is considered trivial
to most chemists.
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forgottenpassword
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The preparation is given here:
http://www.journal.kcsnet.or.kr/main/j_search/j_download.htm...
[Edited on 4-8-2014 by forgottenpassword]
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Nectarine
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How did you find?
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Nectarine
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I followed the procedure and got a much cleaner product. Thank you! It took about 30 minutes to do add the nitric acid for a 5g reaction. I'd hate to
scale up.
The paper then goes on about purification:
"The product was recrystallized in acetone."
But the product is readily soluble in acetone... Could they possibly mean acetone/water? Would that ever be an implied statement?
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forgottenpassword
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You could try cooling the acetone in salt/ice to see if that helps. Failing that, precipitation from acetone by adding water may help to purify it. If
it needs purifying, that is.
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Nectarine
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I think one of the major issues here is my TLC plates are absolute sh*t! They completely change from one day to the other. One day my starting
material streaks, the next it is one very specific spot. Quite annoying, not sure how it happens.
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