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reactofurnace
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Phthalic acid synthesis
Can anyone suggest how to synthesize phthalic acid using a naphthalene precursor. Wikipedia makes mention of the oxidation of naphthalene using
dichromate. Can anyone provide reaction conditions for this? and what solvents are best to use. Is this an oxidative cleavage type rxn, if so does
anyone know the mechanism.
Also saw this route to making phthalic acid from naphthalene: https://www.prepchem.com/synthesis-of-phthalic-acid/
But the procedure seems relatively dangerous and out of my comfort zone for a home prep.
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Syn the Sizer
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Hello, I am sure it is similar to oxidizing xylenes. It can also be done using KMnO4 as a less toxic alternative. When you oxidize
naphthalene, it should oxidize the first carbons off the benzene ring creating 2 carboxylic groups.
Here are a couple links to videos, one is oxidizing o-xylene and the other oxidizing xylenes and separating the o isomer.
https://www.youtube.com/watch?v=PAARYmBYudg
https://www.youtube.com/watch?v=w5VDZI09Z00
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Fery
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Our forum member Prepic asked me to post the preparation of phthalic acid from naphtalene + KMnO4.
There are already 3 old threads discussing the same topic:
https://www.sciencemadness.org/whisper/viewthread.php?tid=65...
https://www.sciencemadness.org/whisper/viewthread.php?tid=87...
https://www.sciencemadness.org/whisper/viewthread.php?tid=17...
I don't wan't to open new thread for that so I post it here. I would like to kindly ask moderator(s) to eventually move to appropriate place / merge /
split etc.
Here the method which I used long time ago - scanned page from the book and its translation into English:
Attachment: 256_257.tif (524kB)
This file has been downloaded 334 times
naphtalene 2,6 g (0,02 mol)
KMnO4 16g (0,10 mol)
conc. H2SO4 (I certainly used diluted accumulator 38% H2SO4 because as 15 years young boy I hadn't access to conc. acid... well I had 1 L bottle thank
to my schoolmate, but also plenty of accumulator acid which was possible to buy in drugstore, so certainly used accumulator acid keeping concentrated
acid to experiments where diluted couldn't be used)
In 250 ml RBF with condenser attached (I suggest Liebig with wide tube and not too long, certainly shorter than your longest glass rod) is heated
mixture of 2,6 g naphtalene, 16 g KMnO4 and 160 ml of water. It is heated until disappeareance of violet color of KMnO4 (this is hard to observe as
MnO2 prevents to see the color of water solution, it is necessary to let MnO2 to settle a little and observe the clear liquid above it) and until the
liquid loses color above the settled MnO2 (1,5 - 2 hours). It is necessary to periodically stop the water circulation through condenser and push
sublimed naphtalene back into the flask using glass rod. After finishing heating MnO2 is filtered out, filtrate boiled down to 1/3 of its original
volume (to approximatelly 60 ml), 4 ml of conc. H2SO4 is added (I certainly added equivalent amount of 38% H2SO4 and boiled the volume to 50 ml as the
volume of the diluted acid was bigger than concentrated acid). While still hot the paste of MnO2 is added until it dissolved (IIRC not too much of it
dissolved and the solution soon started to contain suspension of MnO2 particles). Already during the addition the phthtalic acid starts to precipitate
in a form of crystalline product. Reaction mixture is heated to boil and such amount of water is added which dissolves the precipitated product. After
finished oxidation a little of active charcoal is added and hot solution is filtered. Filtrate is concentrated and let to crystallize. Phthalic acid
crystallizes in a form of white crystals, which are sucked off and dried between 2 sheets of filter paper. By its sublimation is its anhydride is
obtained, m.p. 128 C. Yield 2 g which is 60,6% of theory. Phthalic acid is white crystalline substance with m.p. 203 C, only very slightly soluble in
water, soluble in alcohol, little in ether.
As I did not have camera that time, I don't have pictures of the experiment itself. But I remember I "cooked" the reaction on a wood stove in my
gradma summer kitchen, so the boil was only very mild, certainly not vigorous. I also remember, that I waited for KMnO4 discoloration for maybe 4-5
hours and only then realized, that it already reacted and violet color was gone, maybe already hours ago, just the colorlessness was not visible due
to MnO2. I also suggest not to boil it too vigorously as then naphtalene sublimes faster. Also stirring should improve performance (mg. stirrer or at
least swirling the apparatus using hand - I did that manual swirling occasionally as melted naphtalene is as a top layer and it is necessary to
increase surface contact to made it to react). Maybe the boil itself is sufficient to mix both phases, but vigorous boil = too fast sublimation of
naphtalene which settles in condenser. I wonder whether it couldn't be performed in a flask without condenser, sitting on mg. stirrer (or at worst
periodically swirl in a hand) with its neck just covered by a plastic foil, at such temp just below the boil (e.g. in boiling water bath so the
content in flask couldn't reach 100 C), so the plastic foil keeps the flask closed and prevents naphtalene loses by escaping.
I still have the vial with the product, the vial is 10 ml. Pictures made just now attached. The label is still readable although it already lost some
color and the paper is somewhat yellowish.
 
I found solubilities of phthalic acid in water here:
https://www.bc.edu/content/dam/bc1/schools/mcas/Chemistry/pd...
"Phthalic acid is very soluble in boiling water, 18 g/100 mL, and is much less soluble in chilled (14°C) water, 0.54 g/100 mL."
[Edited on 9-4-2021 by Fery]
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Fery
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Here I found oxidation of naphtalene with KMnO4 + H2SO4 in acetic acid : H2O 1:1
https://www.researchgate.net/publication/312117264_Kinetic_a...
https://www.researchgate.net/profile/Bijudas-K/publication/3...
this study focused not on yield but on mechanism and reaction speed
acetic acid dissolves naphtalene better than water
worth of trying for producing phthalic acid and focusing on yield
Attachment: 40-0581116.pdf (591kB)
This file has been downloaded 325 times
the bad solubility of naphtalene in water really annoyed me decades ago (2 phases = bad contact of molten naphtalene floating on top of the oxidizing
solution) and also crystals of naphtalene in condenser (maybe if using enough acetic acid naphtalene would be dissolved by acetic acid in the
condenser)
here comparison with KMnO4 alkaline oxidation to phtalonic acid instead of phtalic acid:
https://sci-hub.st/10.1021/j150083a001
Attachment: daly1906.pdf (675kB)
This file has been downloaded 288 times
also interesting oxidation to phthaldehydic acid instead of phthalic acid here:
http://www.orgsyn.org/demo.aspx?prep=cv2p0523
http://www.orgsyn.org/Content/pdfs/procedures/cv2p0523.pdf
Attachment: cv2p0523.pdf (319kB)
This file has been downloaded 249 times
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Triflic Acid
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An interesting thought just popped into my head. What if someone where to put a catalytic amount of of dichromate into an acidic solution of whatever
they wanted to oxidize and then bubbled ozone or something through the solution, so only a bit of dichromate is needed. Saves on the cost, and still
has the ease of a Jones oxidation. No manganese oxides or expensive amounts of chromates.
There wasn't a fire, we just had an uncontrolled rapid oxidation event at the power plant.
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Oxy
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Ozone is nasty gas and I would avoid it if possible. Despite it's toxicity the products of organics reacting with it may be explosive and toxic also.
What else - you can't really control the reaction as you don't know if your substrate is reacting with ozone or dichromate.
However it is easy to do when passing electric current through the solution. You can then use a relatively small amount of oxidizer (like Ce4+) which
will be continuously regenerated
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Triflic Acid
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Yeah, the electric current method seems smarter.
There wasn't a fire, we just had an uncontrolled rapid oxidation event at the power plant.
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Fery
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And acetic acid is quite good solvent for naphtalene and also for some ions, worth of trying the electrolysis...
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Keras
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I’m waking up this thread just to know if someone has tried another strong oxidiser? I can’t really have access to potassium permanganate so I'd
rather spare what I have. Potassium dichromate I would have to make, and I'd rather avoid chromium VI completely for evident reasons of waste
management. I was thinking about Oxone™, i.e. potassium peroxymonosulphate, because I have tons of it. Did anyone tried?
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Fery
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Keras where do you live? I have certainly more than 10 kg of KMnO4.
I did oxidation of naphthalene with CrO3 in acetic acid into 1,4-naphthoquinone.
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Keras
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In France.
I have CrO₃ flakes, but really each time I open the bottle they're stored inside, I recoil instinctively 
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Keras
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Ok so I tried this morning oxidising 1 mmol (~ 100 mg) of naphthalene with 5 mmol (~ 800 mg) of potassium permanganate. Rationale is, you oxidise four
carbons with two oxygens each, so each molecule of permanganate gives up two oxygens, ergo one needs at least four times as much permanganate as
naphthalene.
Naphthalene dissolved in DCM (a few drops are enough) in a 25 mL RBF with dropping funnel and reflux condenser (useless, in hindsight). Heated until
the DCM boils, dripped in the permanganate (~15 mL + 2 mL 50% sulphuric acid). Probably almost instantly particles of manganese dioxide stuck to the
wall of the flask. Continued stirring for one hour at 70 °C. Dismantled the thing, geared up for vacuum filtration. No traces of sublimated
naphthalene. No real smell, too.
Assuming 100% yield, 1 mmol of phthalic acid weighs 166 mg, soluble in 30 mL of water, especially hot. So I put a bed of Celite™ to avoid clogging
my sintered disc with particles of manganese dioxide and got a clear, straw yellow filtrate. No trace of DCM, no purple colour, so I guess all the
permanganate had reacted.
Boiled the ~30 mL of water down to 10 mL. Put it in the fridge → Nothing. Yellow water, is all. Faint aroma of something decisively different from
naphthalene, but zero product.
I’m not sure what happened. Could all naphthalene have been oxidised to carbon dioxide? Did I use too much permanganate? Bad solvent? No idea at
this point.
Going to retry later in the week using other oxidising products: Oxone, sodium percarbonate, bleach, ammonium persulphate.
PS: Cleaning the flasks and stir bar is easy using HCl which dissolves manganese dioxide.
[Edited on 25-11-2024 by Keras]
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Fery
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I did the oxidation of C10H8 with 10% KMnO4 water solution. At oxidation state no DCM, no H2SO4. It ran well. I posted it here:
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...
The disadvantage is processing quite voluminous MnO2 by repeatedly extracting with hot water and filtering on Buchner.
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Keras
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There are several elements I don’t understand:
– You did the oxidation in neutral pH, didn’t you? I thought cleavage worked only in acid conditions?
– Why acidify the resulting mixture at the end? On the contrary, I would’ve basified the mixture to get soluble sodium phthalate, filtered out all
manganese dioxide and then reacidified the filtrate to get the free acid.
I’ll retry with the amounts you suggest, only 10 times smaller.
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Keras
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There are several elements I don’t understand:
– You did the oxidation in neutral pH, didn’t you? I thought cleavage worked only in acidic medium?
– Why acidify the resulting mixture at the end? On the contrary, I would’ve basified the mixture to get soluble sodium phthalate, filtered out all
manganese dioxide and then reacidified the filtrate to get the free acid.
I’ll retry with the amounts you suggest, only 10 times smaller.
[Edited on 26-11-2024 by Keras]
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Gualterio_Malatesta
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Quote: Originally posted by Keras  |
Boiled the ~30 mL of water down to 10 mL. Put it in the fridge → Nothing. Yellow water, is all. Faint aroma of something decisively different from
naphthalene, but zero product.
[Edited on 25-11-2024 by Keras] |
Isn't it supposed to be in a form of dipotassium o-phthalate (as someone mentioned here on the forums) after the oxidation reaction? And it should be
acidified to yield phthalic acid which is insoluble in water.
If so, would it be possible to add ascorbic acid, which will make MnO2 dissolve in water and phthalic acid then percipitated by HCl solution? Gets rid
of filtering pesky MnO2.
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Gualterio_Malatesta
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What I don't get in Fery's write-up is why did he have to filter out MnO2 only to add it back again? Wasn't the reaction finished already?
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Keras
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| Quote: Originally posted by Gualterio_Malatesta | | Quote: Originally posted by Keras |
Boiled the ~30 mL of water down to 10 mL. Put it in the fridge → Nothing. Yellow water, is all. Faint aroma of something decisively different from
naphthalene, but zero product.
[Edited on 25-11-2024 by Keras] |
Isn't it supposed to be in a form of dipotassium o-phthalate (as someone mentioned here on the forums) after the oxidation reaction?
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In this case, I had added sulphuric acid to the permanganate solution, and I checked that the pH was at most 1 before filtering. There was a
priori enough water to dissolve the phthalic acid almost completely:
22 mmol/L @ 0°C, 35 mmol/L @ 20 °C, 640 mmol/L @ 95 °C
I had about 15 mL of water (before rinsing) so that should’ve contained at least 500 µmol or 87 mg of product. Not much, but enough to form a
visible precipitate.
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Sir_Gawain
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Working with sub-gram amounts, it’s very easy to lose your product (or volatile reactants). 87 mg is such a tiny amount it’s not surprising you
didn’t get any product. It’s also possible that the acidified permanganate solution was to harsh of an oxidizer and simply oxidized to CO2. If I
have some free time this week I’ll try this reaction myself.
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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Keras
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| Quote: Originally posted by Sir_Gawain | | Working with sub-gram amounts, it’s very easy to lose your product (or volatile reactants). 87 mg is such a tiny amount it’s not surprising you
didn’t get any product. It’s also possible that the acidified permanganate solution was too harsh of an oxidizer and simply oxidized to CO2. If I
have some free time this week I’ll try this reaction myself. |
My supply of potassium permanganate is very small (a few grams), and I like to work microscale (I find it cute, and it consumes less reactants). I
have usually no problems, for example the nitrosation of phenol by nitrous acid works very well even at a sub-gram scale.
But yeah. I agree over-oxidation is probable. I’ll try oxidation with dilute nitric acid (37%), since apparently that pathway works for oxidising
o-xylene to phthalic acid – although it might lead to nitration instead. Unfortunately I don’t have any potassium chlorate left atm.
[Edited on 26-11-2024 by Keras]
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bnull
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The yellow may be due to alpha-naphthoquinone. It also seems to be one of the side products of an electrochlorination of naphthalene in
hydro-alcoholic solution of HCl I tried fifteen years or so ago. Aside from a heavy oil (which I suppose is a polychlorinated naphthalene), there was
something soluble that became red when the solution was made strongly alkaline. Or maybe the naphthoquinone was formed from the polychloro-naphthalene
when I added the base.
If you can spare another 800 mg of permanganate, try the procedure again, this time adding a small quantity of dichromate (the tip of a penknife will
do) and no acid. Dichromate seems to catalyse oxidations by permanganate. I'm not really sure of how it works, maybe dichromate acts like an acid.
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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teodor
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| Quote: Originally posted by Keras | In France.
I have CrO₃ flakes, but really each time I open the bottle they're stored inside, I recoil instinctively
|
I use it for years (as well as chromic acid to clean glassware) and still good. There is more danger with insoluble chromates (e.g. when unexperienced
people try to get K2Cr2O7 from stainless steel in a pot and usually end with a different chromates mix) which can penetrate a cell membrane and cause
DNA mutation, but with CrO3 it is much less probably because in tiny quantities it reacts with surface fluids and the cell wall itself. Usual
laboratory techniques and protection should be enough.
On my experience low solubility of potassium permanganate requires big flasks for mediocre yield.
[Edited on 2-12-2024 by teodor]
[Edited on 2-12-2024 by teodor]
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Keras
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That’s a better assumption indeed! However, when I added sodium hydroxide in an attempt to solubilise any phthalic acid produced, no red colour was
ever produced…
| Quote: Originally posted by bnull | | If you can spare another 800 mg of permanganate, try the procedure again, this time adding a small quantity of dichromate (the tip of a penknife will
do) and no acid. Dichromate seems to catalyse oxidations by permanganate. I'm not really sure of how it works, maybe dichromate acts like an acid.
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Unfortunately I have no dichromate at hand, but yeah, I guess I can still spare 800 mg of KMnO₄ before running out. I am however, currently
distilling/concentrating 20° white vinegar cleaner into glacial acetic acid. It seems that oxidation of naphthalene to phthalic acid in glacial
acetic acid is well documented. All the experiments I did so far used DCM and water, and that didn't seem to work well. Maybe it needs an acceptable
co-solvent to work properly?
Attachment: Kinetics and Mechanism of Naphthalene Oxidation in Acetic Acid.pdf (371kB)
This file has been downloaded 10 times
[Edited on 2-12-2024 by Keras]
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teodor
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You can look https://library.sciencemadness.org/library/books/Experiments...
Page 233 for further inspiration with the acetic acid solvent.
Also, I recommend just to buy it glacial.
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Keras
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Lol, I have glacial acetic acid somewhere, I just can’t seem to be able to get my hand back on it. :/ In any case, I don’t need it glacial, the
paper I joined used 50% concentration, which is easily feasible starting from 20% w/w.
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