My reaction was performed in pyridine and at the end of the reaction I evaporated the pyridine with co-evaporation by toluene. Then to obtain my cpd (benzoylated sugar) I just worked up (water/ethyl acetate) the organic layer containing my cpd. But on doing TLC the organic layer still contained pyridine showing a tailing on the TLC plate. I want a very convenient method to remove the pyridine because my cpd is an intermediate and should be pure for the next step.
Try washing the organic layer with 10-15% CuSO4 solution, the pyridine would form a complex with copper that would go into the aqueous layer. Any residual copper in the organic layer can be removed by washing with a saturated EDTA solution.
Well, in my experience, I usually used mild acidic solution (e.g. 2~3 % Aq. HCl) during work-up. Briefly, evaporate pyridine as much as you can, wash the organic layer with mild acidic aq. sol'n, then wash with sat. aq. sodium bicarbonate, and water or brine consequently unless your target product includes amino group. I used this procedure when I synthesize nucleoside derivatives.
Try azeotroping with heptane, instead of toluene. Add heptane, evaporate on rotavap, repeat if necessary several times. Works pretty well!
All three mentioned above are perfect. If any functional group tolerance issue, washing your organic layer with planty of water is the one which can be tried. You can use mild CuSO4 solution (~5%).
I don't know what your cpnd looks like, but if you have only minor ammounts of Pyridine left column cromatography should do the job!
I do like Tae Cho, but use 5-10% aq. citric acid instead of dil. HCl.
I would use aq. solution of CuSO4.5H2O for washing the organic layer of required product containing pyridine. I have used this method and it worked well. You might like the beautiful blue color of CuSO4 sulotion as well..
1/ In the first step use the pyridine/heptane azeotrophic destillation in a vacuum rotary evaporator following the prescription of Frank Kayser.
2/ Evaporate trace amounts of pyridine in the product with a modeate stream of N2 at temperature of 60 - 80 oC /water bath with round bottom flask immersed into it/ until the smell of pyridine vanishes.
3/ Keep your sample for several days in a dessicator with drying and pyridine trapping agent 98 % H2SO4.
Note: all above mentioned methods of the authors are correct and easy to use.
R.S.
Method using 15% aqueous solution of CuSO4 is very good, the use of CuCl 2 in the same concentration is even better.
usually acidify with 1-2% HCl solution to convert the excess pyridine to pyridinium hydrochloride which can dissolved in water and the resulting compound extract with organic solvent. However, the co evaporation of reaction mixture with toluene e.g. 5mlx3 time is efficiency method to remove the residue of pyridine.
Aqueous solutions of HCl or copper sulfate are indeed efficient for pyridine removal. In the case of copper sulfate, there is a colorimetric indication. Pyridine gives a violet color with copper sulfate which is therefore deeper than the blue color of copper sulfate. When the violet color no longer appears, that means that removal of pyridine is complete.
The azeotropic method is convenient. Toluene is particularly efficient for this purpose. Alternatively, cyclohexane may be used. Its efficiency is similar to benzene without having high toxicity. Of course, cyclohexane is less efficient than toluene (you need more) but is more volatile and easier removed at the rotary evaporator.
It is no doubt this forum is about knowledge and experience transfer and I have found a lot of it there. In this particular case, I do co-evaporation with toluene since most of my compounds are heterocycles, that could form complexes with copper or salts in HCl acidic medium as well. So, you have to select the method you will use, based on your compound(s) chemical structure(s).
Good luck
When I worked at NIST, then NBS, for Dr. Bruce Coxon in the old Chemistry Building, I made numerous sugar derivatives such as yours under his direction. He always had me use ice cold 10% HCL 3X followed by equivalent rinses with ice cold DI water. It always worked for me, so I would weigh in for the mild HCl washes. Cheap and easy and no issues with metals that might muck up NMRs - copper in water can do that as I once used tap water on the fly and Bruce could tell that I had from the NMR.
I think - with vacuum rotary evaporator with bath at minimum 65-70 degrees, for minimum 1 hour.
Repeat the toluene co-evaporation process for three to 4 times, it affords the pyridine free compound. If this protocol is failed, use aqueous HCl (if your compound is stable in acidic medium, and no free amine group) in cold condition during work up. This process will furnish your product without pyridine.
It is well-known that pyridine is used as scavenger for HCl. So the pyridine in your research may be removed by its reaction with dil. HCl which gives pyridinium chloride salt & this salts goes to the aqueous layer in extraction. Collect the organic layer, add drying agent to it (e.g. Na2SO4) , and decant the liquid. Now test your liquid product with TLC.
After concentrating the EtOAc layer, containing your compound of interest, at the rotatory-evaporator you can get rid of the final traces of pyridine by connecting to a high vacuum line overnight.
In my experience, I had allways used, after the first evaporation, 5 small portions of toluene, with distillation in rotavapor after each one. Normally this is enough to get it out of the reaction mixture.
That's fine whatever you have done to remove pyridine from the reaction mixture. After removing the pyridine as much as you can by co-evaporation with toluene, you just leave the reaction pot for one or two days (until the pyridine smell disappeared) to open air without capping (do not put lid on mouth of RB flask). Definitely you will get results. I have much experience with this problem early.
I reccommend the same method fully described by Nizar Matar.
Pyridinium chloride salt goeseasily to the aqueous layer in extraction procedure or you can simpli remove it by filtration from organic mixtures.
The above answers look fine if it essential that you run in pyridine as solvent. If you can run in another solvent with pyridine as a base, I am a big fan of using poly-vinylpyridine. Since it is a heterogeneous solid, you can remove it by simple filtration.
try to use ice mild HCl and then wash with brine sln. it works pretty well.
I always prefer to add 1 N HCl solution if the compound is stable towards acidic condition. To remove the trace amount of pyridine you can use toulene or water and remove solve under reduced pressure.
I used and worked well.
Unless your target compound is a pyridine derivative, use mild acidic solution (e.g. 1-5 % aq. HCl) during work-up.
In my case, the expected product is a chelating ligand and Cu would then pick up the target products just as well as it is picking pyrdine. Thanks for all the nice answers. It has helped me too.
I would suggest to use CuSO4 and 1N HCl too according to nature of your molecules.
Evaporiting pyridine (under vacuum) followed by extraction (HCl 1M/ EtoAc) should work
I would suggest also repetitive washing with water in the case your compound is not soluble in water
I was successful also triturating the solid with MeOH and diethyl ether. At H-NMR you will notice disappereance of the pyridine signals
Good luck!
Regarding Richard T. Taylor answer, sir poly-vinyl pyridine , does it work when pyridine is used as solvent also.i am using pyridine as solvent for tosylation of sugar followed by acetylation , do u suggest the use of poly-vinyl pyridine in this case
The most convenient ways often involve complexing the pyridine with other molecules. this will change the chemical proporties of both, easing extraction. One method is co-evaporating the pyridine off with toluene. Adding Toluene in a 1:1 ratio will form a complex with a lower boiling point, taking both the pyridine and toluene out of the mixture. Another method is complexing the pyridine with CuSO4. This is done by washing the reaction mixture with a saturated aqueous CuSO4 solution and then separating the layers. The pyridine will remain in the aqueous layer with the CuSO4.
Keep in mind that these, and most other similar processes (like acid washes) will only remove free pyridine, and that some pyridine may be left behind in complexes with your product (salts).
The best option is to use a high vac, if it is available. High vac is efficient in removing high boiling liquids like pyridine and DMF. Then, extract the residue with EtOAc or DCM and wash carefully with IM HCl and then neutralize by bicarbonate wash. I guarantee you, there will be none left after this. Some people do use CuSO4 solution instead of HCl
Best method to remove pyridine from a reaction mixture is to wash the reaction mixture with hydrochloric acid twice.
What about the situation where you are using pyridine as the solvent in a sulfonation reaction with pyridine-SO3 complex and at rxn temp of 90 C everything is soluble. But upon cooling your product ppts out. Being a sulfonate it is not soluble in many if any organic solvents, except you guess it, pyridine. So, now I have a buchner funnel full of rxn product and it stinks like hell. I tried several cycles rotovap with toluene, or heptane, and it helps, but still there. Tried lyophilizing but apparently my machine needs servicing. You see, most of the methods above address methods that involve molecular products that are soluble in an organic solvent. But that's a hard proposition for a sulfonate. Most are strictly water soluble it seems.
OOPS! There is an almost identical column on Research Gate and I thought I was responding to that. I will try to find that discussion.
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