Dear Yasser Fakri Mustafa I assume that the answer to your question is rather simple, i.e. that the pale yellow sample is just not really pure. Of course I can't say this for sure because I don't know the exact structure of your product. Quite likely the very pure compound is colorless. I suggest that you recrystallize both samples and see if the resulting crystals have e.g. the same melting point. Good luck!

Dear Frank T. Edelmann

I already did that. After re-crystallization, the two products have the same melting point and different colors.

Regards

Dear all, what is the catalyst? Is it a solid catalyst? My Regards

https://link.springer.com/article/10.1007/BF03051833

https://www.researchgate.net/publication/298155775_Synthesis_of_coumarins_via_a_Pechmann_condensation_using_heterogeneous_catalysts

Dear Yasser Fakri Mustafa there could still be a possibility that the yellow sample contains contains a minute amount of a highly colored impurity. Did you try column chromatography? Do you plan any subsequent reactions? If yes, it a minor impurity perhaps doesn't matter.

Dear all, the appearance of colored product may be an indication of degradation. According to the attached file, the optimum reaction time and temperature should be respectés, going over these two parameters leads to degradation. My Regards

Dear Abdelkader BOUAZIZ

The reaction conditions are the same, and the catalyst is Conc. H2SO4.

Thank you so much for your response and valuable contribution.

Regards

Dear Frank T. Edelmann

I will try that. Is it possible based on your expertise that the same product has two different colors?

Thank you so much for your response and valuable contribution.

Regards

Dear all, solid catalysts are much more efficient and easy to eliminate. Possibly there is (are) byproduct(s) of only one phenol hydroxyl group reacted. My Regards

Dear Yasser Fakri Mustafa if both samples have already been recrystallized, it is perhaps a rare case where you have different types of crystal modifications. In the end you need an X-ray crystal structure determination.

If this coumarin derivative is insoluble in nonpolar solvents, I would like to suggest something fast and may be effective to purify. Please try to wash your colored sample with distilled hexane or pentane and check the change in color.

Dear Yasser Fakri Mustafa I fully agree with Mohamed Salem in that simple washing with n-pentane or n-hexane could provide a simple way to remove colored impurities. These solvents are often very useful especially for removing some oily material. It''s often advisable to pre-cool them prior to the washing step. By the way, I would always prefer n-pentane over n-hexane, as the latter is significantly more toxic.

Thank you Professor Frank T. Edelmann for this valuable advice and detailed description

Dear Frank T. Edelmann , Abdelkader BOUAZIZ , Mohamed Salem

Thank you very much for your valuable opinions and kind contributions. I will try to take the comments into the consideration.

Regards

Dear Yasser Fakri Mustafa I hope that the answers by Abdelkader BOUAZIZ , Mohamed Salem and me were useful. Please let us know at some stage what the outcome of this interesting story is. Good luck!

Dear Frank T. Edelmann

I will do that. In the next week, the second chapter of this story will start.

Regards

Dear all, I found the attached file extremely important to add. My Regards

The colour difference is possibly contamination of product with metalic coloured impurities which is difficult to remove by mere solvent purification .one can remove these impurities either by acid treatment to compound if it is inert towards acids or by vaccum distillation in its liquid state and then allowed to cool to become solidification.it will definately remove the colour impurities if charcoal treatment is unable to do it. One more stratergy is to disolve in solvent and pass through clay,diatomious earth or pullar earth to absorb colour impurities on surface of these absorbents to get clean coloured product of desired colour.

Dear Yasser Fakri Mustafa I think that Nitin Dnyandeo Patil added another very good aspect to this discussion. In our experience too, a very good purification method is filtration through a small column packed e.g. with silica gel. If minor metal-containing impurities are present, these are like being adsorbed on the column and stay behind.

Dr. Frank T. Edelmann is the right person to answer such questions by their experience.

Dear Tanvir Singh many thanks indeed for your kind words. Highly appreciated! 😎 I just have 40+ years of experience, which now pays off. Our field of research, organometallic chemistry comprises both inorganic and organic chemistry. That's we we also have a long-standing experience with e.g. the preparation of organic ligands.

This is the reason Frank T. Edelmann I recommended your name on this platform.

Dear Abdelkader BOUAZIZ

Thank you so much for sharing the valuable article. You assistance is highly appreciated.

Regards

Dear Nitin Dnyandeo Patil

Thank you very much for your valuable opinion and contribution.

Regards

Dear Frank T. Edelmann

Thank you very much for your valuable and significant contributions.

Regards

May be impurities of inorganic metals or catalyst. So give wash with pentane to the pale yellow colour compounds .Hope it will help to you .

Air oxidation of the starting phenol or hydrolyzed coumarin could form a colored dimer. Try working up the reaction by adding bisulfite to the aqueous wash.

Dear Naimish Kumar Verma

Thank you very much for your valuable opinion and kind contribution.

Regards

Dear Richard Boden

Thank you very much for your valuable opinion and kind contribution.

Regards

thanks and welcome!!!

Dear ,Yasser Fakri Mustafa, it is a common thing, that traces of coloring substances can give a substance a visible tint. The concentrations are mostly that low, that they dont affect standard analytivcal methods. In some cases it is possible to remove them by adding granulated activated charcoal during recrystalisation. but in most cases it is only a cosmetic problem.

Regards

Dear Andreas Pingel Keuth

Thank you very much for your valuable opinion and kind contribution.

Regards

I am glad if it helps you

Dear Yasser Fakri Mustafa I'm still wondering if you really have to care about the pale yellow color of your product at all. If you plan any further derivatization reactions with the compound, you can perhaps achieve a more efficient purification in the next step.

Dear Frank T. Edelmann

Thank you very much for this advise, you are always a supportive man.

"Vielen Dank, mein Professor"

Regards

Dear Frank T. Edelmann , Abdelkader BOUAZIZ , Andreas Pingel Keuth , Naimish Kumar Verma , Mohamed Salem , Nitin Dnyandeo Patil , Richard Boden

The pale yellow product was transformed into the off-white product as it washed with cold n-hexane.

Thank you very much for your support and assistance.

Regards

Dear Yasser Fakri Mustafa many thanks indeed for providing this very interesting information. Great to hear that one of the suggested purification procedures was successful.

In my opinion this thread nicely illustrates how RG should ideally work. A researcher asks an interesting question about a real scientific problem and receives a number of high-quality answers from experts. In the end the problem can be solved. Absolutely perfect. RG at it's best!