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Topic: Detecting -NO2 group in aromatic 3-nitrophtalic acid  (Read 1767 times)

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Offline ArbuzToWoda

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Detecting -NO2 group in aromatic 3-nitrophtalic acid
« on: July 14, 2020, 05:56:14 AM »
Hi!
I proceeded according to this paper: https://pubs.acs.org/doi/pdf/10.1021/ja01684a028 and synthesised 3-nitrophthalic acid. I recrystallised the reaction mixture from water two times. The first recrystallization batch had melting points of 186-187°C open tube, while the second one was 207-208°C open tube, much closer to the theoretical 210°C. That would mean I got rid of the unwanted isomer, 4-nitrophthalic acid, which melts we much lower temperatures (160°C). So far it all looks idyllic, but I'm concerned with a couple things: the recrystallised solid doesn't really form yellow solutions, more like a murky greenish/greyish. It also forms crystals very similar to those of unnitrated phthalic acid (my crystals photo 1, crystals of phthalic acid photo 2). I'd like to find some way to check for the presence of nitro group in my product, preferably chemical, as I don't have the access to things like NMR.
Thanks for all suggestions!
edit: forgot to add that the melting point for phthalic acid is around 207C, dangerously similar to my sample, hence the concern.

Offline rolnor

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #1 on: July 14, 2020, 01:26:16 PM »
The cheapest way to se what you have is TLC, you need a UV-lamp, you can buy cheap ones on ebay. The TLC-plates are expensive though. Meltingpoint is near useless when the startingmaterial is so close to the product. I think if you have a spot on a TLC-plate of your product it will be yellow if you expose it to ammonia, the startingmaterial will not give any color. The RF should be a little different to but it is a bit problematic that you have a very polar compound, maybe EtOAc with 5% HOAc could be a good system. Is there anyreason to think that your reaction fail, do you have good reagents? Also did you use phtalic anhydride, not phtalic acid?

Offline ArbuzToWoda

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #2 on: July 14, 2020, 06:17:33 PM »
The cheapest way to se what you have is TLC, you need a UV-lamp, you can buy cheap ones on ebay. The TLC-plates are expensive though. Meltingpoint is near useless when the startingmaterial is so close to the product. I think if you have a spot on a TLC-plate of your product it will be yellow if you expose it to ammonia, the startingmaterial will not give any color. The RF should be a little different to but it is a bit problematic that you have a very polar compound, maybe EtOAc with 5% HOAc could be a good system. Is there anyreason to think that your reaction fail, do you have good reagents? Also did you use phtalic anhydride, not phtalic acid?
Thanks for the answer! I don't really have reasons to think that it isn't my product, maybe I'm just a bit paranoid. The whole synthesis' success (luminol) depends on its weakest link, so if I proceed without assurance I might just waste my time. I've seen some videos and papers about making one's own TLC plates with alumina, CaSO4 and glass microscope plates. Do you think it would work? Also, why would the spot with my material turn yellow with ammonia? Wouldn't that just produce the ammonium salt (presumably colorless)? Concerning the reaction, I purified my phthalic anhydride by sublimation (it's a lot of work! I recycled around 40 grams solely by sublimating it on heat and capturing what settled on the beaker's walls), so I'm pretty sure that I started with the anhydride, and not acid. Thanks for the response once again anyway!
edit: I forgot to add that my concerns started, because on all of the videos the mother liquor from the reactions was bright yellow, while mine was barely grayish/yellowish. Maybe I did too good of a work in not letting NO2 be produced during the nitration and it didn't really dissolve into the mother liquor? Not sure.

Offline rolnor

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Offline ArbuzToWoda

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #4 on: July 15, 2020, 04:53:40 AM »
The idea I had about ammonia depends on the ammonium-salt being yellow, I know that p-nitrophenol gives this yellow color.
I looked on Luminol, some nice chemistry. Do you have hydrazine?
It can work to make you own TLC-plates but you can buy these on ebay; https://www.ebay.com/itm/25-TLC-Aluminium-Sheets-20-x-20cm-Silica-Gel-60-F-Pack-of-25/124105656879?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D225086%26meid%3D3d69ddf502f6424da23d42571aa4ab66%26pid%3D100005%26rk%3D1%26rkt%3D12%26mehot%3Dlo%26sd%3D322497310226%26itm%3D124105656879%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWebWithDarwoV2BBEV2b&_trksid=p2047675.c100005.m1851
I'd buy these, but they're ludicrously expensive for my purposes. That one pack is basically the cost of a new hotplate. I don't have hydrazine, but I don't need it either. All of the reasonable preps use hydrazine sulfate, which frees tiny amounts of hydrazine in situ during prolonged hearing with an acetate salt. I've already made the hydrazine sulfate using the Hoffman rearrangement on urea.

Offline rolnor

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #5 on: July 15, 2020, 12:52:45 PM »
Yes, those TLC-plates are expensive but its difficult to suggest any other analysis method that is cheaper.
Maybe you can make a small scale experiment with the material you have? If you have followed the procedure carefully it should be OK with the nitration.

Offline ArbuzToWoda

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #6 on: July 15, 2020, 02:13:10 PM »
Yes, those TLC-plates are expensive but its difficult to suggest any other analysis method that is cheaper.
Maybe you can make a small scale experiment with the material you have? If you have followed the procedure carefully it should be OK with the nitration.
I bought the ingredients to make my own plates out of microscope slides, silicagel and plaster of paris (calcium sulfate hemihydrate). However I'm worried about the way of visualizing my TLC results - most plates have some sort of a UV indicator, fluorescent dye inside them (I think its Zn2SiO4 in most), but mine probably won't. I thought about adding some fluorescein I could make to the silicagel mixture - sounds promising, but I think the eluent would just dissolve it and make it useless. What do you think? I also did some solubility experiments today, here are the papers claiming about the mole fraction solubility of phtalic and 3-nitrophtalic acids: https://sci-hub.tw/https://pubs.acs.org/doi/10.1021/je0604737
https://scihub.tw/https://www.researchgate.net/publication/244465808_Solubilities_of_Terephthalic_Acid_Phthalic_Acid_and_Isophthalic_Acid_in_Tetrahydrofuran_Cyclohexanone_12-Diethoxyethane_and_Acetophenone

I took some time and calculated, that in 20C 3-nitrophtalic acid's solubility in THF should be around 75g/100g water, while phtalic acid's 17,27g/100g water. Not sure if my calucations were correct, so if you wish I can send a photo. Anyways I measured out 7.5g of my crystals and added them to 10g of THF. Most didn't dissolve, but some did. I'm a bit confused now.

Offline rolnor

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #7 on: July 15, 2020, 03:04:48 PM »
I dont understand when you give the solubility like that, 75g/100g water, do you mean 75g/100gTHF?
Yes, the fluoreceine will just dissolve. You can spray the plate with some reagent like ammoniummolybdate to se the spots without using UV or place  the TLC-plate in a jar with Iodine, this will stain most compounds. Can the solubility really be as hign as 75g/100g THF?

Offline ArbuzToWoda

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #8 on: July 15, 2020, 03:41:13 PM »
I dont understand when you give the solubility like that, 75g/100g water, do you mean 75g/100gTHF?
Yes, the fluoreceine will just dissolve. You can spray the plate with some reagent like ammoniummolybdate to se the spots without using UV or place  the TLC-plate in a jar with Iodine, this will stain most compounds. Can the solubility really be as hign as 75g/100g THF?
Wow, I cannot concieve how dumb was just what I wrote. I obviously meant 75g/100g THF. The water popped in from habit. I think I'm going to use the iodine method, though I'd love to find some way to use UV. I too was surprised by the solubility, but you can check it out yourself - it says that 100 x1 (100 times the mole fraction solubility) was around 20. That would mean that x1 is 0,2. Therefore 0.2 moles of product dissolves in 0.8 moles of THF, so 42 grams of product dissolves in 57.6 grams of THF. I did the proportion and it's around 75g-100g THF.

Offline ArbuzToWoda

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #9 on: July 15, 2020, 03:44:03 PM »
And the same stands for the phtalic acid - it was 17.8g per 100g THF.

Offline AWK

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #10 on: July 15, 2020, 03:46:29 PM »
Many years earlier, before the chromatography of 1903 was born (discovered by a laboratory assistant at the Institute of Plant Physiology of the (Russian) Warsaw University in Poland), chemists were able to identify newly obtained compounds by a mixed melting point. Why don't you try it?

My students made luminol (effectively!) according to this recipe:
https://www.semanticscholar.org/paper/A-PERFORMING-SYNTHESIS-STRATEGY-OF-LUMINOL-%2C-A-R-%C4%83-PETRE-Hubc/74b84376b8fff8181d2911c6b310465c7d34d0db
but there were some problems with reductionof 3-nitro-phthalhydrazide  and isolation of amine.
AWK

Offline ArbuzToWoda

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #11 on: July 15, 2020, 04:31:17 PM »
Many years earlier, before the chromatography of 1903 was born (discovered by a laboratory assistant at the Institute of Plant Physiology of the (Russian) Warsaw University in Poland), chemists were able to identify newly obtained compounds by a mixed melting point. Why don't you try it?

My students made luminol (effectively!) according to this recipe:
https://www.semanticscholar.org/paper/A-PERFORMING-SYNTHESIS-STRATEGY-OF-LUMINOL-%2C-A-R-%C4%83-PETRE-Hubc/74b84376b8fff8181d2911c6b310465c7d34d0db
but there were some problems with reductionof 3-nitro-phthalhydrazide  and isolation of amine.
That's my maternal country! What do you mean though, by mixed melting points?
Thanks

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AWK

Offline ArbuzToWoda

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #13 on: July 15, 2020, 06:53:00 PM »
I'll certainly try the mixed melting point thing. The synthesis you linked looks great, but also depressingly more cumbersome. I'd have to redo the whole nitrophtalic synthesis and buy new reagents. Also it remarks quite a few times that the difficult separation of 3 and 4 isomers leads to failed syntheses, which is weird, considering both UC235 and NileRed successfully synthesised luminol using the phtalic anhydride route. I can't find the articles (5) they're reffering to either. I'm grateful for the option though!

Offline rolnor

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Re: Detecting -NO2 group in aromatic 3-nitrophtalic acid
« Reply #14 on: July 16, 2020, 08:51:28 AM »
You just add some iodine crystalls to a jar, place the TLC in and put on a lid, if you are in a hurry you can varm the bottom of the jar with a heating-gun to get iodine-vapor faster. It stains almost all compounds. You should dry the TLC-plate first to get rid of solvent.

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