Chemistry Reference
In-Depth Information
Fig. 4.3
Types of
carboxymethyl chitosan (
a
)
O
-carboxymethyl chitosan
and (
b
)
O
,
N
-carboxymethyl
chitosan
a
O-CH
2
COOH
H
H
O
HO
O
H
NH2
n
H
O
-CMCh
b
O-CH2COOH
H
H
O
O
HO
H
NH-CH2COOH
H
n
O
-
N
-CMCh
The production of
O
-CMCh and
O
,
N
-CMCh depends on the reaction conditions
as illustrated in Scheme
4.1
.
Preparation of
O
-Carboxymethyl Chitosan
Okimasu [
64
] prepared CMCh, obtaining the product either as sodium salt with the
amino group present in the free base form or as the hydrochloride salt of the amine
with the carboxymethyl groups present in the free acid form. The sensitivity to
added electrolyte increased with the increase in the extent of carboxymethylation.
The
O
-alkylation of Ch in which the amino group is protected by Schiff's base
formation has been studied by Plisko and coworkers [
65
,
66
]. In this case,
N
-salicylidene Ch was treated with monochloroacetic acid in the presence of an
alkali and a diluent, such as isopropyl alcohol or xylene, to give
O
-carboxymethyl-
N
-salicylidene Ch which was converted to
O
-CMCh by hydrolysis of the Schiff's
base under acidic conditions. Other procedures obtaining the product by using two
different techniques either microwave [
67
] or thermal [
68
] technique.
Microwave Technique
Ge and Luo [
67
] prepared CMCh in aqueous solution under microwave irradiation
by treating firstly the Ch with NaOH solution and then adding the required amount
of chloroacetic acid. The product is then precipitated in acetone as white powder.
