Editing Synthesis O-carboxymethyl chitosan (section)

== Preparation of O-carboxymethyl&nbsp;Chitosan (OCMCh)  ==

=== [[Image:O-carboxymethyl Chitosan synthesis.png]]  ===

=== Protocol 1  ===

Carboxymethylation was carried out by stirring chitosan (5 g) in 20% NaOH (w/v, 100 mL) for 15 min. then '''monochloroacetic acid '''(15 g) was added dropwise to the reaction mixture and the reaction was continued for 2 h at 40 ± 2 °C with stirring. Then the reaction mixture was neutralized with 10% acetic acid, then was poured into an excess of 70% methanol. The produced carboxymethyl chitosan was filtered using a G 2 sintered funnel and was washed with methanol. The product was dried in a vacuum at 55 °C for 8 h to give 6.5 g of dried carboxymethyl chitosan. The degree of substitution of CMCh was determined to be 0.75&nbsp; 

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=== Protocol 2  ===

2 g of LMWSC (Low molecular weight water soluble chitosan)&nbsp;was immersed in 25 mL of 50% (w/v) NaOH solution and&nbsp;alkalized for 24 hours. The alkalized LMWSC was filtered<br>and then transferred into a flask, after which 5 g of '''monochloroacetic acid in isopropanol '''was added in a dropwise&nbsp;manner for 20 minutes. This flask was allowed to react for<br>a further 8 hours at room temperature (RT). The reactants&nbsp;were filtered to remove the solvent, and the filtrates were&nbsp;then dissolved in 100 mL of water, thereafter the pH was<br>adjusted to 7.0 using 2 N HCl. The product was precipitated&nbsp;by ethanol and the precipitates were harvested by filtration.&nbsp;Residual ethanol was removed by vacuum drying. 

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=== Protocol 3  ===

Carboxymethyl chitosan was prepared by method as suggested by Sun et.al [6]. Chitosan (10g), sodium&nbsp;hydroxide (10g), isopropanol (50 ml) and water (50 ml) were added into a flask to swell and alkalize at 50 o C for&nbsp;1 h. The monochloroacetic acid (15 g) was dissolved in isopropanol (20 ml), added into the reaction mixture&nbsp;drop-wise for 30 min and reacted for 4 h at the same temperature, then stopped by adding 70% ethyl alcohol&nbsp;(ethanol, 250 ml). The solid was filtered and rinsed in 70-90% ethyl alcohol, and vacuum dried at room temperature.&nbsp; The product was Na salt CC (Na-CC). Na-CC (1 g) was suspended in 80% ethyl alcohol aqueous solution (100&nbsp;ml), hydrochloric acid (10 ml, 37%) was added and stirred for 30 min. The solid was filtered and rinsed in 70-90% ethyl alcohol to neutral, vacum dried.