Kinetics of N-Deacetylation of Chitin Extracted from Shrimp Shells Collected from Coastal Area of Morocco

Abstract

Chitosan was obtained from the alkaline N-deacetylation of -chitin, derived from shrimp shells (SS) collected from the Moroccan coast. Effects of temperature, NaOH concentration and reaction time on the kinetics of deacetylation were studied. The degree of deacetylation (DD = 75%) was obtained at T = 120 °C and CNaOH = 12N in a single step for 6h. It was found, from FTIR studies, that the removal of acetyl groups from chitin occur very fast for the reaction time t < 180 min and then becomes constant after, revealing two steps in the deacetylation of chitin following a first-order kinetics for each of them. The second step is considered the limiting step that has, in the temperature range of 25 – 120 °C and maintained CNaOH = 12N, a low apparent rate constant. The activation energy of this step is about 48.76 kJ/mol. The biopolymer (Chitin and chitosan) produced were characterized by X-ray diffraction.

Quantitative Analysis by IR: Determination of Chitin/Chitosan DD

“…The chitin deacetylation process followed the pseudo-first-order kinetics for all the temperatures studied (25, 80, and 120°C) and at the same alkaline concentration (12 N) [3]. The Table 8 showed that the values decreased as a function of temperature.…”

“…The temperature in this step is a factor that weakens the binding of the acetyl groups and accelerates the deacetylation reaction. Ahlafi and al [3] also found that the DDs increase as the NaOH concentration and temperature increase as the time of reaction increases. These reached a maximum of 63% and 71% for C NaOH = 12 N at T = 80 and 120°C, respectively.…”

“…[23] Ref. [3] T°C/C NaOH mol/l 7.5 10 12.5 C NaOH mol/l T°C DD 40 -1 2 8 180 38 60 10 14 20 10 120 45 80 24 60 67 12 60 55 100 26 68 78 8 180 38 120 28 74 90 10 120 45 Table 6. Evolution of DD in relation to temperature at different concentrations of the base [3,23].…”

“…But it was not until 1894 that Hoppe-Seyler gave the "modified chitin" the name chitosan [1]. Chitosan has some advantageous properties, such as biocompatibility, biodegradable polymer of high molecular weight, nontoxic, and antimicrobial activity, that encourage its applications in many fields including agriculture [2,3], paper industry, food and textile industries, pharmaceutics [4,5], biochemistry, biotechnology, cosmetics, biomedical applications [6][7][8], environment, and water treatment [9][10][11][12][13]. The properties of chitin and chitosan depend considerably on the degree of deacetylation (DD), a parameter defined as the mole fraction of deacetylated units in the polymer chain [14,15].…”

Cytotoxicity of Low, Medium and High Molecular weight Chitosan’s on Balb/c 3T3 Mouse Fibroblast Cells at a 75-85% De-acetylation Degree

“…This reaction pathway, when allowed to go to completion (complete de-acetylation) yields up to 98% produce. Chitosan may be further purified by preparation of solutions in acid followed by neutralization and precipitation [11,12].…”