Process and Kinetic Mechanism of Elimination of Chlorine Combined in Molecule of Bleached Shellac

Purpose: To investigate the process and kinetics of the removal of chlorine integrated in a molecule of bleached shellac applied as pharmaceutical excipient.
Methods: Sodium ethoxide was employed to react selectively with the carbon atom connecting with chlorine, which induced the removal of chlorine by means of elimination reaction. The technologic parameters, such as dosage of sodium ethoxide, temperature, time, etc, influencing dechlorination efficiency were studied. Furthermore, the kinetics of chlorine removal was investigated by analyzing the variation of chlorine content with time and temperature.
Results: The results demonstrate that the optimal conditions for eliminating combined chlorine are to react with 3.15 g of sodium ethoxide at 90 ^oC for 90 min. Under the optimal conditions, the content of chlorine in the final products is 0.28 % w/w, which is far smaller than that in the products prepared without dechlorination (2.6 % w/w)..
Conclusion: Combined chlorine, which is harmful to the properties of shellac, can be removed in the presence of sodium ethoxide by means of elimination, and the reaction for chlorine content of shellac is first order reaction.

Keywords
Enteric coating; Sustained release; Elimination method; Nucleophile; Shellac; Natural products