ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 7, pp. 1162!1166. + Pleiades Publishing, Inc., 2006.
Original Russian Text + E.N. Chebotok, V.Yu. Novikov, I.N. Konovalova, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 7, pp. 1172!
AND POLYMERIC MATERIALS
Depolymerization of Chitin and Chitosan
in the Course of Base Deacetylation
E. N. Chebotok, V. Yu. Novikov, and I. N. Konovalova
Murmansk State Technical University, Murmansk, Russia
Knipovich Polar Research Institute of Marine Fishery and Oceanography, Murmansk, Russia
Received February 2, 2006
Abstract-Depolymerization of chitin and chitosan in the course of deacetylation in an alkaline medium was
studied, and the influence exerted on the process by the nature and concentration of the alkali (NaOH, KOH)
and salts (NaCl, NaI, KI) was examined.
Base hydrolysis of chitin (CTN) and chitosan
(CTS) is one of the main chemical methods for modi-
fication of these natural polysaccharides; it mainly
involves cleavage of the acetamide bonds resulting in
deacetylation [1, 2].
Depolymerization of the macromolecules in alka-
line solution is considerably slower than the deacetyl-
ation and, as believed by many researchers, is due to
oxidative degradation of glycoside units rather than
to hydrolysis of glycoside bonds [3, 4].
This study was aimed to refine the factors affecting
the depolymerization of chitin and chitosan in the
course of their base deacetylation.
Chitin was recovered from Kamchatka crab shells
by the standard procedure [5, 6]. Chitosan was pre-
pared by deacetylation of chitin with 50% aqueous
The extent of saturation of the examined solutions
with oxygen or nitrogen was recorded with an Anion
4151 ion meter (Infraspak-Analit, Russia) equipped
with an ammetric sensor of the oxygen partial pres-
It is known that solutions of chitosans with the
degree of deacetylation exceeding 85% are virtually
transparent in the UV and visible range. At a degree
of deacetylation less than 55%, chitosan and chitin are
insoluble in weakly acidic aqueous solutions; there-
fore, chromatographic analysis of such samples re-
quires special choice of suitable solvents and eluents.
The conditions of chromatographic analysis of chitin
and chitosan were close to those used for solutions of
chitosan in HCl.
For this purpose, we modified the procedure for
preparing carboxymethylated derivatives of chitins
(CMCTN)  with the aim to use them for determin-
ing the molecular weight and molecular-weight distri-
bution by exclusion chromatography.
Samples of chitins and chitosans with various
degrees of deacetylation were acetylated with a 20%
solution of acetic anhydride in ethanol at 4oC for 24 h.
Similar procedure for pretreatment of chitooligosac-
charide samples was used, e.g., in mass spectrometry
of chitin hydrolyzates [3, 8]. The products of exhaus-
tive acetylation were treated with monochloroacetic
acid in alkaline solution  to obtain CMCTN:
Carboxymethylation was performed in isopropyl
alcohol at 4oC for 3 days. After the reaction comple-