Your compounds were crystallized from Water/ ethyl acetate mixture.

And I think it will not well solubilize in aquous solution.

Usually we utilize MeOH. Try Methanol at first with sonication.

Some case of more polar compounds, DMSO also good solvent.

In case of Flavonoids and most polyphenols, they are well soluble in MeOH.

In case of more non polars such as fatty acids, carotenoids, you can use hexane.

Good Luck...

Maybe alcohols or acetone will help, but it depends largely on the analysis jobs you mean to do. Good luck.

Thank you very much Byung-Hun and Wang. I have actually tried methanol but not with sonication. I will now try methanol with sonication and acetone too.

MeOH or CH2Cl2 should work. For further details, please refer Chebil et al., 2007 DOI:10.1021/je7001094 Solubility of Flavonoids in organic solvents.

Thanks RIswanto and Limna.

May be you can Increase the solubility by increasing solvent polarity at constant

temperature.

First try with Acetone if not try with Pyridine , I hope it can work.

Usually we use MeOH, if no success; then you can try with DMSO or DMF. Good Luck!

You need to first let us know the purpose for solublizing the compound, if it is for chromatographic analysis you need to use the mobile phase, otherwise methanol usually does the trick or a hydroalcoholic solution

Try the solubility with Ethanol or Methanol, Just warm it and check for solubility. You can also use a mixture of polar and non polar solvents. Good Luck

First make sure the white solid you have is flavonoide or probably inorganic salt, if it has organic compound character, try combine solvents like methanol \water and if still insoluble heat till 40 or 50 degrees, If still not soluble dissolve in triflouroacetic acid, if still insoluble then finally try DMSO, if not soluble I would go to non polar solvent like toluene, if not I would use conc sulfuric acid as last choice.

Like Jawad suggests, be sure first, you have not a mineral precipitate or crystallization. This question was treated a few days ago on ResearchGate by Dr Helmi Yousif Alfarra (How to check if crystals are organic or inorganic compounds?). You should first try to ascertain this point by following all the very good advices given in the many answers to this question.

Thereafter, really, it depends on the nature of your "flavonoid". Do you mean flavonoid (stricto sensu) with a yellow color (like quercetin)? In that case, there should not be any structure that could not re-disolve, at least into very polar solvent such as MeOH or even, mixture of water and MeOH (usually, these flavonoids are better "water-soluble" in alkaline medium since they form salts, thus more polar and more soluble. But, it is just to check to possibility: do not try on all your stuff because in such conditions, they also are very sensitive to oxidation! For instance, you could put a very tiny piece of crystal into a UV cell and add MeOH + 1 drop MeONa to measure rapidly a UV spectrum and to see if there is a chromophoric nucleus in good accordance with such a structure.

If it is a "flavonoid", sensu lato, then you could have, flavanones, flavanols that all should be quite soluble in MeOH. If having colored (pink, dark purple crystals) then, you may have anthocyanins. In our hands, we have many examples of crystals of such series of flavonoids that, when formed (in acidic conditions, with a counter ion like chloride), never redissolved again! When they crystalize, they purify a lot and lose their impurities that were able to dissolve them when present! If this is your case, a good procedure would be not to purify them totally in order to keep them "soluble".

The solubility of flavonoids in aqueous solution is very poor, specially in acidic solutions. Please, try with organic solvents such as ethanol or methanol, like it was previously suggested, and good luck!

Try organic solvents instead such as chloroform, ether, alcohols and organic acids

Please remember, in prolonged chromatographic separations, we may get silica(white residue) also when some final fractions are concentrated. There are color tests to detect flavonoids at a preliminary level.

Good luck!

you can try with DMSO or DMFor pyridine . Good Luck!

try polar solvents (methanol, DMSO) some warming/heating) and ultrasonication

The histrory of the product must be reviewed as it si quite strange talking about a mixture of it crystallising from a mixture of two immiscible solvents.It may even be inorganic! DMSO is a good solvent for organic compounds, generally, but not if you want to recover your product. Your other option is to attempt peracetylation of a small portion with pyridine/acetic anhydride assuming presence of alcoholic or phenolic groups

You can try with hot water.

You can use DMSO/DMSO with ultrasound (or even its hexadeuterated form for NMR analysis) but beware, once that your compound get dissolved the removal of this solvent should cost high efforts as well as high vacuum and a small vessel in order to evaporate it, otherwise forget about your sample or put it to crystallize. Hope this help in your research.

Try to use DMSO before to add water or other solvent.

try THF, some times it solved our problems, it is expensive but easy to reuse after rotavap, you can check its purity by density and reuse in column chrom.

Disperse the solid in methanol followed by ultrasonication. In my experience this will dissolve most flovanoids. Hopefully you are not dealing with silica!

I sincerely hope it is not silica, but please keep us posted if you are able to go round it.

I think the isolated compound are crystals. Simply put your isolated compound in a glass beaker , add hot water and stir with glass rod. If it is soluble in hot water, will go into solution.

The isolated compound in question is certainly not silica. Silica was not used at any stage of its isolation. Besides, these white crystals have very beautiful characteristic shape, quite different from that of silica. Anyway, based on some good suggestions made by some contributors here I am already having some success in getting it into solution. Thanks to you all.

did you tried solvent ether , chloroform, even then if u r facing difficulty you can hydrolyse the the compound and then u can isolate aglycone portion and in aq. solution u can do TLC etc for the identification of sugar,

DMSO, CDCl3 are of high ability of dissolution, and mixtures of double solvent is also recommended, say CH3OH & CDCl3,

chloroform, DMSO may be tried.

Probably DMSO could be tried to dissolve your flavonoid in this case.

I was recently confronted with similar challenges but finally resolved by dissolving the white crystals in aqueous ethanol upon heating. I think this will work for you. Try it.

Dear Olorunfemi,

The contribution of Victor gives me the opportunity to come back to your problem of solubility of flavonoids.

My only explanation was that extraction from the plant of a category of these compounds was made possible because of the solubilizing effect of some "impurities". My advice was "a good procedure would be not to purify them totally in order to keep them "soluble"".

I changed my mind quite a bit after hearing the genius Professor Robert Verpoorte (University of Leiden), last May, in Brussels. He gave me the answer to what I told you was not understandable when purifying anthocyanins (but this could apply to any other kind of natural compounds, with low solubility)! Have you ever heard of "NADES" (NAtural Deep Eutectic Solvents)? They are very powerful organic solvents made liquid at "room temperature" by formation of deep eutectics upon stoechiometric mixture formation between abundant natural primary metabolites in plant, such as Glc, Fru, choline, aspartic, glutaric, amino ... acids (see the attached very interesting paper). As you can see, for instance, Glc and malic acid (solid at RT, mp > 130°C) are liquid until -80° C, when mixed in 1:1 ratio, and this deep eutectic (lowering of the melting point of around 200°C!), not only is natural (present when you isolate secondary metabolites from the plant) but also, is a wonderful solvent for them...

Upon purification of these metabolites of interest, you get rid of all of the "small molecules" such as Glc, saccharose, ... and you no longer are able to dissolve your secondary metabolite in any organic or aqueous solvent!

I am pretty sure (this is the case for us) that if you first prepare eutectic "liquids" your stuff will be soluble in one or all of them !

You can take advantage of this crucial information in extending the conclusion of this paper to all your experimental extractive processes ... from now.

Hope to have helped you to "solve" your problem!!!

Jo Vercauteren

Many thanks to Victor Barku and Joseph Vacauteren for sharing your experience with me. I will try the suggestions you have given, I also appreciate others who have given useful suggestions.

If you got crystals, measure its melting point. It will help in your partial compound identification. Recrystallize using a suitable solvent and then remeasure melting point. A sharp melting point value indicates a pure compound (crystal that melts over a very narrow temperature range). A pure compound will always be more soluble to a given solvent as compared to a mixture of different compounds.

DMSO is usually a good solvent for most compounds with a little heat if necessary. Also if you have beautiful crystals single crystal X-ray would provide structural confirmation.

I agree with Rao. Try sonication in different solvents.

see my paper about cirsimarin

John Hasrat

Thanks Eseyin for asking such a query. This week I encountered a similar dilemma. My compound of interest eluted in 80% Aqueous methanol and upon concentration, I obtained white crystals which are insoluble in most organic solvents. Thanks for the invaluable ideas. I hope these will sort me out.

Could you tell us how you finally solubilized your crystals?

I noticed that you did not use any solvents such as EtOAc, or methylene chloride, or chloroform. All easily evaporated. The chloroform-d would be good to get an NMR.