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Author: Subject: Phthalic acid from ZnO + DMF + Napthalene
Prepic
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[*] posted on 4-4-2021 at 03:42
Phthalic acid from ZnO + DMF + Napthalene


Hi all,

I've been interested in the oxidation of Naphthalene to phthalic acid. I found an article (linked below) which claims to have obtained Phthalic acid via the oxidation of naphthalene in air using both DMF and ZnO as catalysts.

I tried to follow their procedure as closely as possible although scaled up. In my procedure, I prewarmed a 500ml flask at 90C and then added 40 ml of Dmf, 1.6g ZnO and 10g of Naphthalene. This is exactly a scaled up version of their oil-bath experiment (same molar ratios). I also ensured there was good stirring.

I attached a Liebig condenser and let the reaction mixture sit for 4 hours(1) (I had a 45 min power interruption midway).

In my work up, I filtered the ZnO and crashed out everything in 200ml ice cold water followed by filtration. I then collected the solids left on the filter and added 4.6g K2CO3 dissolved in 100ml water to form dipotassium phthalate and potassium hydrogen phthalate (depending on yield). I observed no fizzing. After filtering undissolved naphthalene, I added 50ml 32% HCL to the filtrate and no phthalic acid fell out of solution.

My work-up is different form the suggested workup although I think it should work just as well. I don't have CHCl3 on hand and frankly I don't even think their work-up procedure makes much sense in the first place.

Honestly, I found this procedure fishy form the start and didn't actually expect it to work, however I gave it a shot. Does anyone have any experience with this procedure or can guide me on how I could improve or perhaps suggest using another oxidizer? Alternatively, I'd also appreciate if someone "confirm" that this procedure is bullshit. (this is published in Tetrahedron Letters see below)

(1) Following the paper, I was aiming to run the reaction for 3 hours and 15 min.




Attachment: ZnO a versatile agent for benzylic oxidations.pdf (110kB)
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Boffis
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[*] posted on 4-4-2021 at 05:23


Hmm.: I presume the oxygen required for the oxidation is atmospheric. In which case shouldn't you blow air through the mixture? I simply can't believe that oxygen from the air can diffuse into the reaction mixture without being actively forced through mixture or running under pressure to allow the reaction to occur in a microwave in a matter of 6-8 minute. In the long reflux/ heating method the flask is effectively protected from the atmosphere by the vapour so the same issue persists. to oxidize 10 millimoles of naphthalene requires that 1 litre of oxygen at STP must be absorbed. The carbon dioxide produced would effectively blanket the mixture in the flask unless forced aeration were used. So yes I detect a noticeable smell of bulls*** here.

I would be more credible if it had some means of supplying air/oxygen to the reaction mixture.
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[*] posted on 4-4-2021 at 10:21


I produced phtalic acid from naphtalene by refluxing in aqueous KMnO4. Then filtered out MnO2 and acidified the filtrate by HCl. If you wish I can find you the experiment and translate into English.



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[*] posted on 4-4-2021 at 18:59


I for one would be glad to see that write-up.
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[*] posted on 4-4-2021 at 20:47


Quote: Originally posted by Fery  
I produced phtalic acid from naphtalene by refluxing in aqueous KMnO4. Then filtered out MnO2 and acidified the filtrate by HCl. If you wish I can find you the experiment and translate into English.
It would be nice to see that, but please post it in a different thread as the method that you describe is well known, while this thread is focused on a different, rather dubious, but if it works, potentially very nice new method.

I don't have high hopes for this method, for the same reasons that Boffis outlined. I'm also always wary of reactions that use a metal oxide, with no mention of how the material was obtained or prepared, since the properties of oxides can vary widely due to numerous factors including particle size, calcination, and purity, among others. You aren't going to oxidize toluene to benzaldehyde using manganese dioxide from a pottery store or a battery, for instance. The grade of ZnO being used here may be similarly critical.




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[*] posted on 8-4-2021 at 09:34


Thanks everyone for the comments, I really appreciate the "reality check" about just how much air is required and also the suggestions about looking at the ZnO catalyst.

I think i'll look into trying to prepare zinc oxide in numerous methods first before trying this reaction again with the air pump to give it one last best shot.
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