Russian Journal of Applied Chemistry, Vol. 78, No. 5, 2005, pp. 791 793. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 5,
2005, pp. 807 809.
Original Russian Text Copyright
2005 by Gizatulina, Chebotok, Novikov, Konovalova.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Kinetics of Acid Hydrolysis of Acetylglucosamine
G. A. Gizatulina, E. N. Chebotok, V. Yu. Novikov, and I. N. Konovalova
Murmansk State Technical University, Murmansk, Russia
Knipovich Arctic Research Institute of Marine Fishery and Oceanography, Murmansk, Russia
Received January 26, 2005
Abstract The kinetics of acid hydrolysis of N-acetylglucosamine at different temperatures and reagent con-
centrations was studied. A mathematical model of the hydrolysis was proposed. The rate constant and activa-
tion energy of deacetylation were calculated.
Utilization of large volumes of chitin-containing
waste of crustaceans involves usually chemical hy-
drolysis of chitin and chitosan. Under these condi-
tions, chitin is hydrolyzed to its monomers: glucos-
amine (GA) and acetylglucosamine (AGA). Complete
depolymerization of chitin and chitosan is usually per-
formed in an acidic solution at elevated temperatures
[1]. Under these conditions, the glucoside bonds in the
polysaccharide are ruptured to form the monomers.
Deacetylation occurs in parallel with depolymeriza-
tion. The deacetylated monomer is usually isolated in
the form of its salt of the acid used for hydrolysis. The
study of the mechanisms of acid hydrolysis of chitin
and chitosan as influenced by the degree of deacetyla-
tion and molecular weight of the initial polysaccharide
and hydrolysis conditions (temperature and acid con-
centration) is of both practical and theoretical interest.
by the reaction [8]
C6H11NO5 + (CH3CO)2O
C8H15NO6 + CH3COOH. (1)
Acetylation was performed as follows. A 900-ml
portion of AV-17-8 anion exchanger converted into
the CO form by treatment with 10% aqueous solu-
3
tion of sodium carbonate was placed into a flask
equipped with a stirrer. A 900-ml portion of 0.38 M
aqueous solution of D-glucosamine hydrochloride
[75 g (0.46 mol) GA HCl] and 90 ml of ethanol
(w = 96%) were added at 0 5 C. Acetic anhydride
(45 ml, 0.64 mol, w = 99%) was added in small por-
tions at 0 5 C. The reaction mixture was stirred for
3 h at 0 5 C. The resin was filtered off, washed with
500 ml of distilled water, and regenerated.
The filtrate and wash waters were evaporated under
reduced pressure (10 20 mm Hg) at 50 60 C to a
viscous syrup containing crystals. Ethanol (75 ml,
w = 96%) was added, and the resulting mixture was
left to crystallize at 0 5 C for 12 15 h.
Acid hydrolysis of chitin and chitosan was exten-
sively studied [1 5]. However, the kinetics of this
process was not understood and the rate constants of
its elementary steps were not determined. Previously
we suggested a mathematical model of acid deacetyla-
tion of chitin [6, 7]. We found that the chitin deace-
tylation is described by the first-order kinetic equation
and the dependence of the reaction rate passes through
a maximum at the hydrochloric acid concentration
The crystals were filtered off, washed with 300 ml
of acetone (chemically pure grade) to remove water,
and dried in a vacuum. The N-acetylglucosamine yield
was 73.5% of the theoretical yield corresponding
to Eq. (1).
w
= 29.8%.
HCl
N-Acetylglucosamine was hydrolyzed in hydro-
chloric acid with a concentration from 10 to 37.2%
at 40, 60, and 80 C. The hydrolyzate was neutralized
first with 2.7 M NaOH and then with 0.1 M NaOH to
pH 7.0, filtered through a Schott filter (pore diameter
no larger than 10 m, POR 10), and analyzed for
AGA and GA content (M).
The aim of this study was to estimate the rate con-
stant and activation energy of AGA deacetylation and
to determine the hydrolysis rate of the acetamide bond
as influenced by the degree of polymerization of the
polysaccharide.
EXPERIMENTAL
The AGA content was determined by the procedure
We used N-acetylglucosamine (AGA) prepared by described in [9]; the total AGA + GA content, by the
acetylation of D-glucosamine with acetic anhydride procedure from [10]. The GA amount was calculated
1070-4272/05/7805-0791 2005 Pleiades Publishing, Inc.