Dear Mr. Prabhu,

It depends on the functional group present in the compound. If the molecule has only carbon & hydrogen in it then such molecules are not much soluble in methanol which is very polar compared to chloroform & ethylacetate. For example naphthalene is sparingly soluble in methanol but highly soluble in chloroform or EtOAc. Chloroform & EtOAc are preferred solvents as they are immiscible with water which again helps to get compound free from water.

Hoping you got the point,

with regards,

Sheela

Yes i agree with sheela, solubility of organic compounds are depends on its polarity, also plant extracts may have polymeric compounds and high molecular weight compounds, polymers and high molecular weight compounds will dissolve in non polar compared to polar solvent due to its mol. wt.

if the molecular weight increases the polarity may decrease as the no of hetro atoms (functional groups will be comparatively less)

i hope this helps!

Regards

Selvan

also i need to add one more point,

polarity H2O>> Acetonitile>Methanol>Ethyl acetate> Chloroform, therefor not only the polarity is responsible for the solubility, functional group of the solvent also a mater

here you can find water is more polar but it will not dissolve all the polar compounds, also many protein will dissolve in methanol and precipitate in acetonitrile.

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The solubility of one substance in another is determined by the balance of intermolecular forces between the solvent and solute, and the entropy change that accompanies the solvation. Factors such as temperature and pressure will alter this balance, thus changing the solubility.

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A popular aphorism used for predicting solubility is "like dissolves like". This statement indicates that a solute will dissolve best in a solvent that has a similar chemical structure to itself. This view is simplistic, but it is a useful rule of thumb. The overall solvation capacity of a solvent depends primarily on its polarity.

For example, a very polar (hydrophilic) solute such as urea is very soluble in highly polar water, less soluble in fairly polar methanol, and practically insoluble in non-polar solvents such as benzene.

In contrast, a non-polar or lipophilic solute such as naphthalene is insoluble in water, fairly soluble in methanol, and highly soluble in non-polar benzene.

The solubility is favored by entropy of mixing and depends on enthalpy of dissolution and the hydrophobic effect.

Synthetic chemists often exploit differences in solubilities to separate and purify compounds from reaction mixtures, using the technique of liquid-liquid extraction.

I hope this helps!

Regards

Selvan

You can use the concept of solubility parameter in order to predict solubility

I agree with Sheela Krishna to good extent,however I would like to present the answer in my own way... as follows....>

Note that Methanol is like water --llysoluble with water.. --while plant extracts are likely to be higher carbon chain molecules and hence they would be more hydrophobic. Higher the carbon chain higher is their hydrophobilicity and hence less tendency to dissolve in methanol ( which is strongly hydrophilic)

SO "greater hydrophobicity of plant extracts is the predominant reason of its insolubility in methanol"

correction of mistypes

Note that Methanol is like water --fully soluble with water...

Why does one use ethanol and methanol If they both similar polarity?

Leyla, while their polarity is similar some plant extracts have to be extracted by ethanol if the relevant pharmacopeia demands it. Also as previously mentioned, methanol is toxic whereas ethanol obviously far less so. Final point I'll make is that methanol is much easier to evaporate off than ethanol therefore it preferred where extracts can be dried to residue and reconstituted in a solvent of choice, typically the analyst's mobile phase in HPLC for example.

Whether two chemicals can dissolve together depends on the similarity of the chemical structure, and/or on the interaction between them (eg, whether the hydrogen bond can be formed between two chemicals).

One of main methods to check if they are miscible, is to obtain these two chemical's solubility parameters, see: http://en.wikipedia.org/wiki/Hildebrand_solubility_parameter

If the difference in the solubility parameters of these two chemicals is less than 0.5 cal1/2 cm-3/2, then it is very likely to dissolve each other.

Good Luck

George

PS: If the chemical is a polarity one, the solubility parameter is high (such as water's 23.4, methanol's 14.5), while non-polar solvent has low value (such as n-pantane's 7.0)...

I don't know if you have a mixture. In this case, the addition of methanol (highly polar) might cause the precipitation of less-polar compounds, meanwhile the medium polarity for ethyl acetate and chloroform promotes higher levels of solubility.

Thank you all

Compounds derived plants contain terpenoids alkaloids, flavonoids carbohydrate, peptide etc. Solubility of compounds depend upon polarity, more polar compounds dissolve in more polar solvent, methanol is more polar than chloroform and ethyl acetate and in methanol , the compounds which is more polar and have tendency to form hydrogen bond are soluble in methanol, to isolate non polar or weakly polar compound require less polar compound one principle for solubility is like dissolves like