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Author: Subject: A Note on the Synthesis of 3-Nitrophthalic Acid
UranylPeroxysulfate
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A Note on the Synthesis of 3-Nitrophthalic Acid

I was recently attempting the synthesis of 3-nitrophthalic acid. From my research on youtube videos and existing threads on this topic, the synthesis of 3-nitrophthalic acid by nitration of phthalic anhydride does not give good yields. The procedure on https://www.sciencemadness.org/whisper/viewthread.php?tid=12... [1] suggested by benzylchloride1 gave a yield of only 20%. On the same thread, the procedure on Magpie gave a crude yield of only 32% based on phthalic anhydride (without considering the isomeric split of 3- and 4-nitrophthalic acid). NileRed's procedure also didn't give good yields (30% yield for the pure product) [2]. These procedures were all based on the paper written by E. R. Littmann [3]

However, when I tried the exact same procedure (see [1] and [3] for the procedure; I skipped the benzene azeotropic distillation step and instead vacuum filtered the product and dried it in a desiccator) on a scale of 31.7 grams of phthalic anhydride, I got around 25.5 grams of the product prior to recrystallization. This corresponds to a percent yield of 56%, much higher than the yields of others who attempted this synthesis.

My abnormally high yield of 3-nitrophthalic acid surprised me, so I did a bit of research to find out what happened. From the evidence that is available to me, I conclude that the deciding factor of the yield of 3-nitrophthalic acid is the concentration of the nitric and sulfuric acids used. My inference is based on the following:

- I used 71% nitric acid and 98.4% sulfuric acid (concentrations determined by titration with 0.500M NaOH solution from a chemical company and bromothymol blue as an indicator)
- benzylchloride1 used 70% nitric acid and 92% sulfuric acid
- NileRed didn't determine the exact concentration of his nitric and sulfuric acids, so I estimated the concentrations by looking at the techniques he used to prepare them. NileRed's sulfuric acid is made by distillation of drain cleaner, so it is likely around 98% concentration [4]. His nitric acid is made from the distillation of dilute nitric acid [5]. I estimate the concentration of his nitric acid to be around 63%; I'll explain why later in the post.
- The dicarboxylic anhydride group on phthalic anhydride is electron-withdrawing, which deactivates it with respect to Electrophilic Aromatic Substitution reactions such as nitration. So, from a theoretical standpoint, harsher reaction conditions, such as higher acid concentrations, should improve yield.

Based on these pieces of evidence, it seems like the use of >70% nitric acid and >98% sulfuric acid for the synthesis of 3-nitrophthalic acid is critical in getting a good yield. Sulfuric acid of 98.4% concentration can be obtained by boiling sulfuric acid of a lower concentration until the temperature of the acid reaches 337 degrees Celsius (the temperature of the azeotrope). This boiling should be done in a borosilicate flask attached with a fractionating column and boiling stones to prevent loss of sulfuric acid and minimize the chance of sulfuric acid splashing out. Boiling sulfuric acid is very dangerous, so be sure to research and observe all safety precautions when doing it. Nitric acid of >70% concentration, however, is a bit more difficult to obtain. Fractional distillation of dilute nitric acid seems to only give concentrations of around 61-65% (from my experience and NurdRage's video [6]; this is also why I estimated the concentration of NileRed's nitric acid to be 63%. To be more specific, in my experience, if the distillation is done fast, such as 1 drop per second, the concentration will be around 61%; if it is done slow, such as 1 drop per >5 seconds, the concentration will be around 65%). I obtained my 71% nitric acid by drying 63% nitric acid with a stoichiometric amount of phosphorus pentoxide and then distilling. However, phosphorus pentoxide is not widely available, so I recommend making 71% nitric acid by 1) diluting fuming nitric acid (see [7] for how to make this) with 61-65% nitric acid or 2) adding 98% sulfuric acid to 61-65% nitric acid and distilling; the sulfuric acid will absorb about 42% its mass of water [6]. The concentrations of the acids can be determined by titration. I don't recommend using density to determine the concentrations as density measurements are more prone to errors.

To verify my conclusion, I will recrystallize my product next week and report the final yield and purity in a reply to this post. I don't expect to lose much product (I will mostly be removing 4-nitrophthalic acid) as the solubility curve of 3-nitrophthalic acid is very steep (see attachment for more information).

References:

Attachment: Solubility of 3-nitrophthalic acid.pdf (40kB)
Antigua
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I wish you posted this 2 years ago, haha! I used to have a lot of trouble with this reaction. But it worked wonderfully once I used >90% nitric acid. Great yields, very quickly a lot of yellow precipitate. Luminol was subsequently obtained using thiourea dioxide. Very cool procedure for someone who wants to start with synthetic organic chemistry.
Pinnick
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I have some questions:

Doesn't the Anyhydride just hydrolyse back to the phtalic acid by using Nitric acid in these concentrations and if so, how does that influence the reaction? I would assume the acid is harder to nitrate then the anhydride?
Is there a solvent except water wich can be used and has anyone tried before?
Has anyone tried using a nitrate salt and concentrated sulfuric to generate the HNO3 and the [NO]2+ in situ?

I want to try this reaction but I dont want to concentrate nitric acid

UranylPeroxysulfate
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"Doesn't the Anyhydride just hydrolyse back to the phtalic acid by using Nitric acid in these concentrations and if so, how does that influence the reaction? I would assume the acid is harder to nitrate then the anhydride?"

I don't know, but from previous posts on this topic, phthalic acid does seem to be a lot harder to nitrate than phthalic anhydride. So, I would assume phthalic anhydride doesn't hydrolyze back to phthalic acid under these conditions. This could be because sulfuric acid has a higher affinity for water than phthalic anhydride.

"Is there a solvent except water wich can be used and has anyone tried before?"

I don't think anyone has tried it before. In general, using a solvent other than water is more effective when nitrating activated aromatic rings, such as phenol, not deactivated aromatic ring, such as phthalic anhydride. Nitrating deactivated aromatic rings require high acid concentrations and very little solvent.

"Has anyone tried using a nitrate salt and concentrated sulfuric to generate the HNO3 and the [NO]2+ in situ?"

Yes, NurdRage did it: https://www.youtube.com/watch?v=58Ve69s0qD0. However, since I haven't done it before, I can't guarantee it will be high yielding.

[Edited on 24-4-2021 by UranylPeroxysulfate]
UranylPeroxysulfate
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 Quote: Originally posted by Antigua I wish you posted this 2 years ago, haha! I used to have a lot of trouble with this reaction. But it worked wonderfully once I used >90% nitric acid. Great yields, very quickly a lot of yellow precipitate. Luminol was subsequently obtained using thiourea dioxide. Very cool procedure for someone who wants to start with synthetic organic chemistry.

I wouldn't recommend using >90% nitric acid though. Literature sources suggest that using too concentrated nitric acid actually hurts yield. I would stick with 70-75% nitric acid.
zed
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Seems to me, the nitration of Naphthalene, produces a glorious yield of almost entirely the right isomer.

Still, that's just Nitro-naphthalene. Which then has to be oxidized to the Phthalic Acid/Anhydride.

Good points? Well, the last time I was out and about, I could buy Naphthalene for 4$a pound, at my local Wal-mart. Umm. I should reread. It might be easier, to make highly concentrated Nitric acid, from the get-go. Rather than trying to concentrate it. https://www.youtube.com/watch?v=DEEjNQN2dIQ This was interesting. https://www.scitepress.org/Papers/2018/81858/81858.pdf [Edited on 24-4-2021 by zed] [Edited on 24-4-2021 by zed] Fery International Hazard Posts: 503 Registered: 27-8-2019 Location: Czechoslovakia Member Is Offline Better yields when using fuming nitric acid for phthalic anhydride nitration http://www.orgsyn.org/Content/pdfs/procedures/CV1P0408.pdf The idea posted by zed seems to be excellent for home lab. Oxidation of naphtalene gives phthalic acid, 1-nitronaphtalene should yield 3-nitrophthalic acid. Here oxidation of naphtalene with KMnO4 to phthalic acid: https://www.sciencemadness.org/whisper/viewthread.php?tid=15... The nitration of naphtalene could be done with 60% HNO3 and 80% H2SO4, no need concentrated acids. https://www.prepchem.com/synthesis-of-1-nitronaphthalene/ If there is a heaven, it seems not to be materially based. Does chemistry exist there and if yes, how does it look like? Are there good souls well supplied with laboratory equipment, glass, chemicals and information? UC235 International Hazard Posts: 531 Registered: 28-12-2014 Member Is Offline Mood: No Mood I got 35% yield with a mp of 205-213C, so not quite pure but not bad, and sufficient for luminol. I used 98% sulfuric and ~70% nitric. An important point is to allow the recrystallization to sit cold for a very long time. It really does take forever to come out of solution. [Edited on 25-4-2021 by UC235] Boffis International Hazard Posts: 1607 Registered: 1-5-2011 Member Is Offline Mood: No Mood I wonder if the original poster knows how much 4-isomer there is in his product? No melting presented. Each time the crude product is leached with water to remove the 4-isomer some of the 3-isomer is lost too. Check out Vogel 3rd edition p 966, he ends up with only 90g of final double recrystallised 3-isomer from 250g of starting anhydride or a 25% yield. The leachate is still a mixture of 3 and 4 isomers but is very hard to separate by physical means and Vogel recommends esterification as a means of separating only the leached out (ie soluble portion). How many times did you leach and recrystallise your raw nitration product Uranylperoxysulfate? And Vogel uses fuming nitric acid to top up the nitric acid concentration in the reaction mixture but he doesn't report the yield of raw nitration product. The first reported yield has already been leached once and then recrystallised once to give a 30% yield of crude 3-isomer so I think you are being a bit optimistic and fooling yourself. I think you need to recrystallise some more. But before you try anything I suggest you read kmno4's excellant thread and the attached article on the subject http://www.sciencemadness.org/talk/viewthread.php?tid=77130#... UranylPeroxysulfate Harmless Posts: 23 Registered: 11-6-2018 Member Is Offline Mood: Sulfonated  Quote: Originally posted by zed Seems to me, the nitration of Naphthalene, produces a glorious yield of almost entirely the right isomer. Still, that's just Nitro-naphthalene. Which then has to be oxidized to the Phthalic Acid/Anhydride. Good points? Well, the last time I was out and about, I could buy Naphthalene for 4$ a pound, at my local Wal-mart. Umm. I should reread. It might be easier, to make highly concentrated Nitric acid, from the get-go. Rather than trying to concentrate it. https://www.youtube.com/watch?v=DEEjNQN2dIQ This was interesting. https://www.scitepress.org/Papers/2018/81858/81858.pdf [Edited on 24-4-2021 by zed] [Edited on 24-4-2021 by zed]

 Quote: Originally posted by Fery Better yields when using fuming nitric acid for phthalic anhydride nitration http://www.orgsyn.org/Content/pdfs/procedures/CV1P0408.pdf The idea posted by zed seems to be excellent for home lab. Oxidation of naphtalene gives phthalic acid, 1-nitronaphtalene should yield 3-nitrophthalic acid. Here oxidation of naphtalene with KMnO4 to phthalic acid: https://www.sciencemadness.org/whisper/viewthread.php?tid=15... The nitration of naphtalene could be done with 60% HNO3 and 80% H2SO4, no need concentrated acids. https://www.prepchem.com/synthesis-of-1-nitronaphthalene/

I'm aware that nitration of naphthalene followed by oxidation produces 3-nitrophthalic acid with high yield and purity. I chose not to discuss this method because it involves two reactions rather than one and the oxidation step requires oxidants that are hard to obtain. High purity KMnO4 is unobtainable in many areas and is very hard to make using amateur methods. Chromic acid also works, but it is highly carcinogenic.

As for making highly concentrated nitric acid, I forgot to mention that NurdRage has an excellent video on it: https://www.youtube.com/watch?v=CqzrTxshOXM. This method produces nitric acid of 70-80% concentration and is directly usable for the nitration of phthalic anhydride.

I don't recommend nitrating phthalic anhydride with fuming nitric acid. The method presented in http://www.orgsyn.org/Content/pdfs/procedures/CV1P0408.pdf, which uses fuming HNO3, doesn't give a high yield; the crude yield is only 28-31%. E. R. Littmann's paper also suggests that using fuming nitric acid hurts yield. Use ~70% nitric acid instead.

If something does work, sulfonate it.
Fery
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Hi UranylPeroxysulfate, OK, I should try the naphtalene->1-nitronaphtalene->3-nitrophthalic acid on some rainy days. I did oxidations of aromatic compounds with KMnO4 few times (toluene -> benzoic acid, naphtalene -> phthalic acid). I did oxidation of naphtalene with dichromate only once, it was at very low temperature in acetic acid solvent to produce 1,4 naphtoquinone (I used dichromate instead of suggested CrO3 just to try it).

If there is a heaven, it seems not to be materially based. Does chemistry exist there and if yes, how does it look like? Are there good souls well supplied with laboratory equipment, glass, chemicals and information?
UranylPeroxysulfate
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 Quote: Originally posted by UC235 I got 35% yield with a mp of 205-213C, so not quite pure but not bad, and sufficient for luminol. I used 98% sulfuric and ~70% nitric. An important point is to allow the recrystallization to sit cold for a very long time. It really does take forever to come out of solution. [Edited on 25-4-2021 by UC235]

Good point. I'll keep that in mind when I do the recrystallization. A 35% yield is quite good; it is better than all the synthesis attempts I have read about. I hope I wouldn't lose much product from the recrystallization. At least according to my attachment, I wouldn't.

 Quote: Originally posted by Boffis I wonder if the original poster knows how much 4-isomer there is in his product? No melting presented. Each time the crude product is leached with water to remove the 4-isomer some of the 3-isomer is lost too. Check out Vogel 3rd edition p 966, he ends up with only 90g of final double recrystallised 3-isomer from 250g of starting anhydride or a 25% yield. The leachate is still a mixture of 3 and 4 isomers but is very hard to separate by physical means and Vogel recommends esterification as a means of separating only the leached out (ie soluble portion). How many times did you leach and recrystallise your raw nitration product Uranylperoxysulfate? And Vogel uses fuming nitric acid to top up the nitric acid concentration in the reaction mixture but he doesn't report the yield of raw nitration product. The first reported yield has already been leached once and then recrystallised once to give a 30% yield of crude 3-isomer so I think you are being a bit optimistic and fooling yourself. I think you need to recrystallise some more. But before you try anything I suggest you read kmno4's excellant thread and the attached article on the subject http://www.sciencemadness.org/talk/viewthread.php?tid=77130#...

Like I mentioned in one of my replies, a too high concentration of nitric acid actually hurts yield. Vogel's esterification method is quite interesting though, but I already discarded by leachate, so I couldn't do it.

After nitrating 31.7 g of phthalic anhydride, I poured the reaction mixture into 90 mL of water, filtered it, and then leached it with a further 40 mL of water. I think I've done enough leaching. I haven't done the recrystallization yet, so I didn't report the m.p.. I'll do it this weekend. If my yield is still significantly higher than others who have tried this reaction, then it will prove my point that using ~70% nitric acid (not higher, not lower) and 98% sulfuric acid improves yield.

I read kmno4's thread. kmno4 nitrated phthalic acid instead of phthalic anhydride. Although I personally wouldn't do it due to how easy it is to prepare phthalic anhydride, I think it is a good method. Apparently, kmno4 had trouble separating the 3- and 4- isomers, and the isomers form adducts with each other making crystallization difficult. I couldn't comment on this as I haven't done the recrystallization, but I will report my findings once I have done it.

If something does work, sulfonate it.
Boffis
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After nitrating 31.7 g of phthalic anhydride, I poured the reaction mixture into 90 mL of water, filtered it, and then leached it with a further 40 mL of water. I think I've done enough leaching. I haven't done the recrystallization yet, so I didn't report the m.p.. I'll do it this weekend. If my yield is still significantly higher than others who have tried this reaction, then it will prove my point that using ~70% nitric acid (not higher, not lower) and 98% sulfuric acid improves yield.

I read kmno4's thread. kmno4 nitrated phthalic acid instead of phthalic anhydride. Although I personally wouldn't do it due to how easy it is to prepare phthalic anhydride, I think it is a good method. Apparently, kmno4 had trouble separating the 3- and 4- isomers, and the isomers form adducts with each other making crystallization difficult. I couldn't comment on this as I haven't done the recrystallization, but I will report my findings once I have done it. [/rquote]

It doesn't matter what starting material was used, when the nitration mixture is quenched the product is the same mixture of nitrophthalic acids plus unreacted phthalic acid so the work-up is the same. Be aware that this last compound is the least soluble of the three and therefore is you have a lot of un nitrated phthalic acid in your final raw nitration product you will find this accompanies the 3-nitro isomer and hence make the yield look better. You have presented no evidence that your crude product is even largely composed of the 3 isomer, it could be mainly unreacted phthalic acid. I do not believe that your claim of such a great yield can be obtained from such a critically narrow range of acid concentrations in a field that has been so well studied. In Vogel's procedure he uses both fuming nitric acid and azeotropic acid (1.42 c 68-70%), the overall mixture will be much less concentrated than FNA.

There is compelling agreement between the numerous reports and method that the yield for reasonably pure 3-isomers is about 30% at best and that this figure is dependant on the purity of the product. In other words greater purity = lower yield. This is not the same as the % conversion which might be 60%+ 3- isomer; it is the recoverable yield. Your data as presented so far is totally inadequate to support your claim that you have optimised the acid concentrations to maximum yield.
UranylPeroxysulfate
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I said "if my yield [after recrystallization] is still significantly higher than others who have tried this reaction, then it will prove my point that using ~70% nitric acid (not higher, not lower) and 98% sulfuric acid improves yield" and "I couldn't comment on this as I haven't done the recrystallization, but I will report my findings once I have done it". I admitted the shortcomings of my experiment. I didn't claim I HAVE optimized the acid concentrations to maximum yield; I claimed that I WILL claim this if, after purification, my yield is still significantly above 30%. Please read my post more carefully before replying to it.

If something does work, sulfonate it.
UranylPeroxysulfate
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Quick update on my 3-nitrophthalic acid synthesis:

I have recrystallized my 3-nitrophthalic acid and I'm currently waiting for it to fully crystallize. Like what UC235 said, "an important point is to allow the recrystallization to sit cold for a very long time. It really does take forever to come out of solution", so I (somewhat arbitrarily) decided to let it sit for 4 days. From looking at the 3-nitrophthalic acid crystals in the flask, I can tell that there's significantly less product compared to before the recrystallization, which means that my crude product is probably significantly contaminated with 4-nitrophthalic acid.

However, I'm certain that my crude (and recrystallized) product is free of unreacted phthalic acid from the appearance and properties of the crystals; phthalic acid crystallizes out immediately after cooling and form relatively large crystals while my product crystallizes out only after sitting a while at room temperature and form very small crystals.

I started the recrystallization three days ago, so I'll filter off and collect the 3-nitrophthalic acid tomorrow and report on the yield after a few days of drying the product in a desiccator. By then, I'll know whether the acid concentrations I used actually improves yield.

If something does work, sulfonate it.
kmno4
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Your assumption is that phthalic acid gives separate and pure phase in your mixture.
Knowing that the nitro acids form adducts with themselves, it is probable that same phthalic acid gives such adducts too.
Unfortunately, no data are available for 4 and3 nitroacids + phthalic acid + water system (as far as I know).

As I understand, you will do at least melting point determination of your product. Takinkg a substance of unknown composition as the pure one, without any proof, is rather not good chemistry.

Klaszczę w dłonie, by było mnie więcej....
UranylPeroxysulfate
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 Quote: Originally posted by kmno4 Your assumption is that phthalic acid gives separate and pure phase in your mixture. Knowing that the nitro acids form adducts with themselves, it is probable that same phthalic acid gives such adducts too. Unfortunately, no data are available for 4 and3 nitroacids + phthalic acid + water system (as far as I know). As I understand, you will do at least melting point determination of your product. Takinkg a substance of unknown composition as the pure one, without any proof, is rather not good chemistry.

One problem: I do not have a proper melting point apparatus. I usually determine melting points with a thin test tube and an oil bath, and I need significant amounts of product to determine the melting point this way. So, I want to recover the 3-nitrophthalic acid I used to determine the m.p.. So the question is, does 3-nitrophthalic acid decompose significantly at its melting point? If no, I'll do the m.p.; if yes, I'll find a different way to confirm the purity of my product. I'm a bit worried about 3-nitrophthalic acid dehydrating to its anhydride at its melting point as this is known to happen with phthalic acid.

If something does work, sulfonate it.

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