Dear Nirali, the problem I see is that in water with acid you are going to catalyse the reverse reaction as well, the hydrolysis! Look at:J ournal of Molecular Catalysis A: Chemical 245 (2006) 132–140, it might help.

A biphasic system might be more appropriate or a polar solvent where you can disolve your polymer.

Thank you Mr. Boranghi... The problem is that my polymer is not soluble in any other solvent except water. I can mightas well suspend it in any other polar solvent like acetone.. Is the reaction feasible then but them using extreme ph conditions won't work. Can u plz guide me...

Dear Nirali,

One question i would like to ask. Is your polymer soluble in sulfuric acid? If so you can carry out your reaction in sulfuric acid itself say 1 gram polymer fer 1 ml sulfuric acid or so.

Ok.... But won't that degrade the polymer?

I think the biphasic system could work in your case, polymer in water, reagent (Acid Cl) in DCM and the base, well it depends it could go in one or the other depending of what base you are using.

Is your polymer soluble in DMF?

You can try a biphasic system as Laurent suggest, regarding the solubility , is your compound soluble in DMSO or DMF? Try to add small amounts of acid in order to study the solubility behaviour

Dear Alessandor and Amador,

Ya biphasic is a good option.

My polymer is soluble in bith dmso and dmf bur the problem is product recovery as both these solvents have high boiling points.

I was thinking if the reaction is possible in ethanol, thf or acetone. Is that possible.

If your polymer is poorly soluble in DMSO after the reaction finish you can add a co-solvent as Ethyl acetate in order to precipitate the polymer, once the solvent has been added to the reaction media you can isolate your polymer by filtration and you don´t need to remove big amounts of high boiling point solvents.

Regarding your question about reaction condition, in general terms the stability of anhydrides in protic solvents (Met-OH, Et-OH, water…) is very low. So if you need to use them, use a biphasic system or a polar-aprotic solvent.

Use the minimum amount of anhydrous DMSO to dissolve your polymer e.g. 1-2 mL for 1 g. Hence directly add the anhydride use a glove to avoid excessive amounts of atmospheric water and slightly warm the reaction glass to 50-60 oC for two-four hours. I guess that this time should be enough to obtain the desired esther. Once that you have obtained the esther cool the reaction and perform at least four water - chloroform partitions or water-hexane partitions depending on the solubility of your esther. And please use a constant and minimum amount of water in order to extract the highest amount of esther with the extracting solvent ( CHCl3 or hexane). Also the amount of DMSO should be low due to the presence of water. Hope this helps your research.

Have you tried? Or simply asking? Please try and report.

Dear Amador,

As per your suggestion I've tried the reaction in polar aprotic solvet (acetone), but still I'm struggling to get any esterification.

Dear Hiram,

Thanks for the procedure. I'm to apply the esterified product in food matrix. So I'm skeptical about the very use of dmso.

Would the end extraction partitioning help in removal of all dmso? And if the polymer gets dissolved into water, its recovery with acetone is possible. But i just needed that little assurance about no dmso left.

Dear Ranadeep,

I've worked out quiet a lot of solvents and reaction conditions from past many months and still struggling.

With some more information about the polymer structure we may try to suggest something.

Its a food grade anionic polysaccharide i'm trying to esterify using an acid anhydride.

You can try the following; Use p-Toluene sulphonic acid or,ion exchange resin as catalyst and the anhydride itself as solvent. Stir till the polysaccharide is no longer visible (i.e. it has reacted completely) , then work up the mixture.

Thank you Mr Vyas. I'll try this out.

Polymer Degradation and Stability Volume 245, Issues 1–2, 15 February 2006, Pages 132–140

Can anyone help me explain the work published in this paper? The did esterification in aqueous system at pH=8~9. However, how to avoid weak-base catalyzed hydrolysis of ester group?

It could be possible but with a biphasic system not single water medium. You just try varying different aqueous biphasic systems and see whether you could able to get the desired product or not.

All the Best

If the anhydride is liquid, you might try it neat, without solvent.

Thank you Mr. Gobinda and Mr. James for your suggestions..

With my earlier experience, the polysacc takes up the water from the biphasic system and clumps. Probably i have to try a better composition.

I'll try the neat also. Except that it shouldn't breakdown the polysacc due to very low pH.

Keep in mind that your anionic polysaccharide (carboxylated, I assume) is going to buffer out your acid catalyst - you'll need more than a trace amount of acid. Pyridine, DMAP, or imidazole might be a better choice, as you can use them in truly catalytic amounts at mild (7.5-9.5) pH.