Answer to Question #173306 in Organic Chemistry for Ricxley John

Question

Chitosan is derived from the shells of crustaceans. it is only soluble in an aqueous acidic medium but not in organic solvents. When reacted with phthalic anhydride, it forms an amide. The product is no longer soluble in the aqueous medium but now is soluble in organic solvents. 

a) Draw the product of the reaction between chitosan and phthalic anhydride.

b) Briefly explain the behaviour change in solubility of the starting material and the final product.

Answer 1

b) In an acidic environment, the nitrogen atom of the amino group is protonated and an ion is obtained, and the ions are readily soluble in water. Also, the starting compound is too polar for organic solvents. After the reaction, a compound containing a benzene ring is obtained, this significantly impairs the solubility of the compound in water and makes it soluble in organic solvents.