Biomedical Engineering Reference
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Chitosan
H
3
C
O
OH
HN
H
2
N
HO
HO
O
O
O
O
O
O
HO
NH
2
HO
HO
x
y
z
Formic acid
Formaldehyde
70°C
DMC
H
3
C
O
(H
3
C)
2
N
OH
HN
HO
HO
O
O
O
O
O
HO
O
N(CH
3
)
2
HO
HO
x
y
z
CH
3
l
40°C, NMP
TMC
H
3
C
O
(H
3
C)
2
N
OH
HN
HO
HO
O
O
O
O
O
O
HO
HO
N(CH
3
)
3
+
HO
x
y
z
Figure 2.3
Two-step synthetic pathway for the preparation of TMC avoiding O-methylation.
dimethylaminopyridine and sodium hydroxide, are used together. Snyman et al. [13] syn-
thesized TMC with various conditions based on the methods of Sieval et al. [11] and
Hamman and Kotze [13]. They found that DQ was in the range of 22-59%, depending on
the number of repeated reaction steps. DQ was increased by increasing the number of
repeated reaction steps. Moreover, the decrease in intrinsic viscosity and molecular weight
of the starting chitosan correlated with the increase in the number of repeated reaction
steps. This was due to the effects of time, alkali, and temperature. Curiti et al. [14] found
that the chemoselectivity of the N-methylation of chitosan was affected by the addition of
excess sodium hydroxide and iodomethane. Therefore, O-methylation was favored when
a larger excess of these reagents was used. Polnok et al. [15] investigated the effects of quat-
ernization of the chitosan process and types of base. They found that a DQ higher than
75% was necessary to repeat the reaction steps. However, an increase in the number of
reaction steps provided high O-methylation, which would decrease the aqueous solubility
of TMC.
Runarsson et al. [16] synthesized TMC by changing the solvent system from NMP to an
N
,
N
-dimethylformamide/water mixture (50:50) and performed the reaction without the
aid of a catalyst—for example, sodium iodide. This significantly reduced O-methylation
since
N
,
N
-dimethylformamide/water seems to lower the reactivity of the hydroxyl group
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