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Author: Subject: successful method for purifying anthranilic acid(quick report)
B.D.E
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[*] posted on 7-7-2020 at 10:49
successful method for purifying anthranilic acid(quick report)


Hey, this is a quick report on a successful attempt of mine to purify anthranilic acid made from phthalimide via the Hoffman rearrangement.
There's nothing really special about it, but I figured it can't hurt posting it in here, just in case someone would find it useful :)
---

Stuff you'll be needing:
1. Crude anthranilic acid
2. Soxhelt apparatus
3. n-Heptane(other alkanes might also work, although it seems reasonable to assume that those with higher b.p would work better[or at the very least faster]).

The process:
Fill the Soxhelt apparatus with the crude anthranilic acid, add some n-heptane and start refluxing. That's about it.

If larger crystals are desired, you can add a bit of methanol(after the extraction is over) and slowly boil it off. But keep in mind that some of the acid will react to form methyl anthranilate(evident by a grapy odor). Adding ether might be a better choice.
---

pictures & descriptions:
beginning: a brown powder(somewhat sticky)
a bit after the beginning:
q1.jpg - 69kB
end:
q2.jpeg - 67kB
extracted product(after recryst with methanol):
q5.jpeg - 55kB
slower evaporation of the methanol:
q3.jpeg - 62kB
---

full disclosure:
a relatively pure product can be obtained straight from the formation of the acid via the Hoffman rearrangement, if done meticulously.

Unfortunately, stuff like traces of phthalic anhydride/acid in your phthalimide, or uncertainty in the concentration of your hypohalite solution, might make it a difficult goal to achieve.

[Edited on 7-7-2020 by B.D.E]




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DavidJR
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[*] posted on 7-7-2020 at 14:19


I'm surprised that works so well. Useful to know.
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Tsjerk
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[*] posted on 8-7-2020 at 00:00


Why would higher boiling alkanes work faster? The actual extraction is cold right? And how did you evaporate the heptane? I found it quit hard to get rid off in the past.
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B.D.E
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[*] posted on 8-7-2020 at 05:36


Quote: Originally posted by Tsjerk  
Why would higher boiling alkanes work faster? The actual extraction is cold right? And how did you evaporate the heptane? I found it quit hard to get rid off in the past.
ummm, I'm pretty sure that some of the product had ppt after the solution was cooled down. I may check on it again later this day just to be sure.

The extraction was carried via a soxhlet apparatus at ~1atm, with rapid refluxing straight into the body of the extractor. Hotplate was set to 380C. So definitely a hot extraction.

As for getting rid of the heptane, I actually didn't had to. I simply added the methanol directly into the heptane until all of the product had dissolved, then boiled off the methanol, let the solution cool and filtered the product with a sinter funnel. The resulting filtrate was pretty much all heptane, with only trace amounts of the product itself.

Also, at least from my experience, getting rid of excess heptane was never an issue. I just heat it to it's boiling point(or slightly below it) and let it evaporate. It also evaporate relatively fast at rt with a fan on it.

[Edited on 8-7-2020 by B.D.E]




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mackolol
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[*] posted on 8-7-2020 at 06:25


Wow... very useful workup, I will try this for sure with my somewhat crude anthranillic acid. Hydrocarbons sometimes do wonders in terms of purification.
Thanks for sharing B.D.E
One question: should cooling the heptane/AA solution in freezer crash most of the Anthranillic acid from the solution without the need to evaporate excess of solvent?


[Edited on 8-7-2020 by mackolol]
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B.D.E
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[*] posted on 8-7-2020 at 08:06


Quote: Originally posted by mackolol  
...

Glad to hear you find it useful :)

As for your question, I just want to clarify that anthranilic acid is only very slightly soluble in heptane(roughly 1-2 grams per liter at ~80C). (this is also why a soxhlet extractor is an absolute must-have for this workup).

So as long as you don't mind having a powdered end-product, you can just filter the heptane out at rt, right after the extraction is complete, without a significant lost of yield.

[Edited on 8-7-2020 by B.D.E]




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mackolol
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[*] posted on 8-7-2020 at 09:19


Quote: Originally posted by B.D.E  

So as long as you don't mind having a powdered end-product, you can just filter the heptane out at rt, right after the extraction is complete, without a significant lost of yield.
[Edited on 8-7-2020 by B.D.E]

All right, that's what I have thought.
In case of anthranillic acid, I don't see any other point in having bigger crystals, than just aesthetic matter.
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B.D.E
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[*] posted on 8-7-2020 at 12:54


Quote: Originally posted by mackolol  
In case of anthranillic acid, I don't see any other point in having bigger crystals, than just aesthetic matter.

yes, that's about it.
I just wanted a trophy :D




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Heptylene
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[*] posted on 8-7-2020 at 13:33


Nice, finally a use for my soxhlet apparatus! I remember an attempt at making anthranilic acid which gave me a beige powder, but even recrystallization from ethanol didn't remove the beige color. This looks like it will work well!
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[*] posted on 9-7-2020 at 17:09


So is this just a recrystallization of the aa straight out of the reaction of hypohalite and pthalimide? No copper salt purification? If so it seems great bcoz the copper salt thing seems like a hassle.this seems like a great way to clean up a hard to clean product.apart from the glassware requirement
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mackolol
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[*] posted on 10-7-2020 at 00:37


And this is another reason to buy soxhlet exctractor, which I wanted to do for a long time but I'm always forgetting :)
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[*] posted on 5-9-2020 at 04:30


Great find and awesome writeup! Thank you!
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