Dear Annu,

There is a general rule in chemistry says: Likes dissolves in likes. i.e organic solvents dissolves organic substances and inorganic solvents dissolves inorganic substance, and according to this rule chitosan  ( organic substance) will be dissolved in formic acid  and/ or adipic acid (organic solvents).

Best wishes

Chitosan /ˈkaɪtəsæn/ is a linear polysaccharide composed of randomly distributed β-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). It is made by treating the chitin shells of shrimp and other crustaceans with an alkaline substance, like sodium hydroxide.

Chitosan is produced commercially by deacetylation of chitin, which is the structural element in the exoskeleton of crustaceans (such as crabs and shrimp) and cell walls of fungi. The degree of deacetylation (%DD) can be determined by NMR spectroscopy, and the %DD in commercial chitosans ranges from 60 to 100%. On average, the molecular weight of commercially produced chitosan is between 3800 and 20,000 Daltons. A common method for the synthesis of chitosan is the deacetylation of chitin using sodium hydroxide in excess as a reagent and water as a solvent. The reaction occurs in two stages under first-order kinetic control. Activation energy for the first step is higher than the second; its value is an estimated 48.76 kJ/mol at 25-120 degrees C.[2] This reaction pathway, when allowed to go to completion (complete deacetylation) yields up to 98% product.

The behavior of highly charged polymers in aqueous solutions is a complicated business. I think the problem here is probably over-protonation by too-strong and/or too-concentrated acids. (See the attached link.) You want the polymer chains to be extended, not balled up, and this is dependent on the charge and also on the counterion(s). There is probably some optimum level of protonation that provides maximum solubility and minimizes agglomeration. A buffer might be helpful in maintaining the optimum pH, but thermodynamics (i.e. the solubility product) is always a limiting factor.

http://www4.mpbio.com/ecom/docs/proddata.nsf/(webtds2)/150597

Nice addition from James Demers.

Thanks for the answers !!

I agree with Talaat I. El-Emary  answers .