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Topic: Column chromatography of nitrophenole. Odd result, need help  (Read 858 times)

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Offline kncks997

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Column chromatography of nitrophenole. Odd result, need help
« on: September 22, 2023, 08:47:11 PM »
Hello I am new here as I am have struggle with the following.

I did a nitration of phenole using potassiumnitrate and sulfuric acid.

The raw product was seperated via a column chromatography using 10:1 cyclohexane:ethylacetate to get the o-nitrophenole and later 5:1 to get the p-nitrophenole.

I did the chromatography (please see attached table for an overview of the first column I did; all TLC were run with 5:1 except Vial 1-14 there were run with 10:1) and got multiple fractions. As I did this procedure before I figured that the yellow kinda dirty product that came with the 10:1 should have been the o-nitrophenole and the orange product the p-nitrophenole. The solvent 10:1 was switched to 5:1 after vial 30.

Normally the column should go like o-nitrophenole (F3), then some chinone byproduct and the as the most polar product forming H-bondy with the silica the p-nitrophenole (F4), when using the 5:1.

But after taking melting points, NMR and MS the results are really confusing.

Fraction 3 the yellow solid was clearly p-nitrophenole and came with the 10:1 solvent. Fraction 4 an orange solid showed only slight peaks beside solvent and impurities in the nmr that indicate a mixture of everything. The MS showed nothing as the compound was able to ionize. Please not that vial 15-26 were leftover but i added vial 17-26 to fraction 3 and did a secound column to make the product more pure. All fractions of this secound column showed only one compound on the TLC (not to sure about that, only took a TLC of every 4 vial). The NMR attached of F3 that was done after the second column also seems to be not mixed with o-nitrophenole so I guess there was no o-nitrophenole in the secound column and therefore also not in vial 17-26.

My really important question now is what happend to the o-nitrophenole, as before the fraction with the p-nitrophenole (F3+Vial 17-26) I only got black tar and vials that are non active on the TLC.

I have used 5.06 g of potassiumnitrate in 10 ml of water, added 2.7 ml sulfuric acid at 15-20 °C and then added 2.36 g of phenole diluted with 0.25ml of water.
Water and Ethylacetat was added and the aquarious phase was extracted with ethylacetat. This was really messy as it was really hard to seperate the really dark layers of liquid.

I got 2.657 g of raw product and then proceeded with the column chromatography.

Every help or input is really appreciated as I missed the yield and purity for this experiement now for the second time. Now everything depends on a solid protocol to not redo the whole organic chemistry lab next summer for like 2.5 months...helps  ;D

Kind regards  :)

The fraction I thought was the o-nitrophenole was the p-nitrophenole and the p-nitrophenole is whatever.

The p-nitrophenole got no significant peaks in the nmr other then the solvents and impurities.

Now for the main confusion I can not explain where the o-nitrophenole is.
All vials I took before the first fraction where either non UV-active on a TLC or just resulted in some tar inside the glassware after destilation of the solvent.

The raw product weighted 2.657g and I recovered 495 mg p-nitrophenol (as I now know by the NMR).

I also took an MS but the fraction which i thought was p-nitrophenole was not able to ionize acording to the operator....
What could that product be if I cant see it in the NMR and MS?

Offline kncks997

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Need help with impurities in H-NMR of p-nitrophenole
« Reply #1 on: September 22, 2023, 09:14:40 PM »
I have major problems finding a few peaks in my H-NMR of p-nitrophenole.
CDCl3 was the solvent.

As it is really crucial for me to do a nice protocol on this as I messed up the experiment two times, I really want to find as much as possible within the spectra to hopefully not redo the whole 2 months of organic chemistry pls helps  :'( ;D ;D

Here are the chemicals I used.

sulfuric acid

Acetone for cleaning the testtube and died it in the oven, huge peak nontheless

In spectra nr 1 I am looking for the following: the peak at 6.12 ppm douplett, the peak at 3.75 very small multiplett, 1.26 ppm singulett, 0.92 ppm singulett.

In spectra nr 2 I am looking for the following: 5.58 ppm douplett, 1.71 ppm douplett and 0.92 ppm singulett.

Spectra nr 3 is from a messed up fraction from the column chromatography I did with the nitrophenole. It came after the fraction with the p-nitrophenole. Do you guys maybe have a suggestion which peaks can be assinged to which nitrophenole?

spectra 1 and 2 are both the same p-nitrophenole, spectra 2 was just a lager fraction where I added impure vials and  purified it again with a secound column chromatography.

Unfornatly I can not do further analysis then this. Maybe the MS of the compound in spectra 2 helps, I will also attach that.

I really appreciate your help. I am panicing a little bit because organic chemistry really got its claws in me right now and not in a good way.

Kind regards :)

Offline billnotgatez

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Re: Column chromatography of nitrophenole. Odd result, need help
« Reply #2 on: September 23, 2023, 09:35:52 PM »

you had 2 posts in our forum that appeared to be similar
we only post a given question once in this forum per forum rules
I combined them into 1 post to keep all the information intact
Hopefully someone will be able to help with them together

Offline rolnor

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Re: Column chromatography of nitrophenole. Odd result, need help
« Reply #3 on: September 23, 2023, 11:29:57 PM »
I would redo the experiment. Is it really in the procedure to use this little solvent? Its almost neat? Its easy to nitrate phenol, I would use more water and monitor the reaction with TLC before workup. You have done a lot of work, I am sure you will fix this. Also, when you say tar, what mp has the product? Maybe you have it but its slightly contaminated and therefore does not crystalize. NMR should be the best way to analyze, MS is very usefull but sometimes not. They use SiO2 in this reference, I was looking att the mp, its very low, so if you have a heated waterbath it may look like tar because it has not solidified. The purifying procedure is interesting maybe. The reason 0-nitrophenol is so lipophilic is because you have an internal hydrogen bond between the phenol-OH and one of the the NO2-oxygens.
« Last Edit: September 23, 2023, 11:45:46 PM by rolnor »

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