ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 10, pp. 1753!1758. + Pleiades Publishing, Ltd., 2007.
Original Russian Text + E.N. Chebotok, V.Yu. Novikov, I.N. Konovalova, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 10,
AND POLYMERIC MATERIALS
Kinetics of Base Deacetylation of Chitin and Chitosan
as Influenced by Their Crystallinity
E. N. Chebotok, V. Yu. Novikov, and I. N. Konovalova
Murmansk State Technical University, Murmansk, Russia
Knipovich Polar Research Institute of Marine Fisheries and Oceanography, Murmansk, Russia
Received December 25, 2006; in final form, April 2007
Abstract-Structural properties of the initial and reprecipitated chitin and chitosan samples in dry and
wet states were studied.
Base hydrolysis of chitin (CTN) and chitosan
(CSN) is one of the main procedures for deacetylation
of these natural polysaccharides .
The kinetics of deacetylation of chitin and chitosan
was analyzed in [23 4]. It was found that complete de-
acetylation of chitin and chitosan cannot be attained
in a single-stage treatment of these polysaccharides
with concentrated alkali. Several explanations were
suggested for the decrease in the rate of chitin de-
acetylation in the alkaline solutions.
This paper is devoted to elucidation of the mechan-
ism of chitin deacetylation on the basis of published
data and our experimental results.
Chitin and chitosan were prepared in laboratory
by the known procedure  from shell-containing
wastes from king crab processing.
Chitin and chitosan were deacetylated in a 50%
NaOH solution at 100oC. Samples with various de-
grees of deacetylation were prepared from chitin and
chitosan by repeated treatments with 50% NaOH so-
lution at 100oC.
Prior to reprecipitation from NaOH, chitin was
dissolved in alkali by the procedure described else-
where . A suspension of chitin (3 g) in a 40%
aqueous solution of sodium hydroxide (75 g) was
stored for 3 h at 25oC under reduced pressure. The re-
sulting alkaline chitin was mixed with crushed ice
(225 g) at approximately 0oC. The resulting chitin
solution with a 10% alkali concentration was filtered
through a Schott filter in a vacuum. Then, chitin was
precipitated by gradual neutralization of this solution
with HCl to pH 6.5. The precipitate was separated by
centrifugation, and a part of the wet reprecipitated
chitin was dried at 60oC.
Reprecipitation of chitin from acid solutions was
performed as follows. Chitin (10 g) was mixed with
cold concentrated HCl (200 ml), and the resulting
mixture was stored for a day with intermittent stir-
ring. Then, the chitin solution was filtered through
a Schott filter in a vacuum. The resulting solution
was diluted with cold distilled water (3 l) under stir-
ring. The resulting suspension was kept until the pre-
cipitation was complete, and then the chitin precipitate
was separated by centrifugatoin. The precipitate was
washed with distilled water to pH 6.5, and a part of
the resulting reprecipitated wet chitin was dried at
Chitosan was precipitated from an acid solution.
For this purpose, chitosan (2 g) was mixed with
a 0.1 M HCl solution (200 ml), and the resulting
mixture was kept for 18 h until the chitosan com-
pletely dissolved. The resulting solution was filtered
through a Schott filter under reduced pressure and
then was neutralized with stirring to pH 7.5 with
a 0.5 M NaOH solution. The chitosan precipitate was
separated by centrifugation and washed with distilled
water. A part of the wet chitosan was dried at 60oC.
The degree of chitosan deacetylation was deter-
mined by potentiometric titration of the chitosan so-