Chitin alkaline hydrolysis

Figure 11. Relationship of carbon-to-nitrogen content of chitin subjected to alkaline hydrolysis for varying lengths of time, v, idealized chitin (0% deacetylation, N-aeetyl-D-glucosamine, M.W. = 203) a, idealized chitosan (100 deacetylation, glucosamine, M.W. = 161). (Reproduced with permission from Ref. 12 Copyright 1984, Academic Press.)...

Chitosan is a second abundant heteropolysaccharide composed of /3-[l-4]-2-deoxy-2-amino and -2-acetamino D-glucopyranose units [31]. Chitosan is the partial deacetylated (involving alkaline hydrolysis] product of chitin. Chltln is the main component of outer skeleton of small insects, cuticles, and the shells of shrimp, crab, lobster, etc. Chitosan has been expansively investigated in the pharmaceutical industries for the development of various sustained and controlled release drug delivery systems due to its versatile biological activity [as food and non-food items] and excellent biocompatibility. Hirano [22] conducted an experiment with both healthy and infected skin and found the LD50 in case of orally administered mouse to be [>16 g/kg]. Wu et al. [76] worked on... 

Chitosan is prepared by hydrolysis of acetamide groups of chitin. This is normally conducted by severe repetitions of alkaline hydrolysis due to treatment due to the resistance of such groups imposed by the trans arrangement of the C2-C3 substituents in the sugar ring [57]. Thermal treatments of chitin under strong aqueous... 

Chitin is obtained industrially mainly from the shells of marine molluscs. The technology involves the removal of accompanying proteins in dilute sodium hydroxide, calcium carbonate and hydrochloric acid. Partial alkaline hydrolysis of acetyl groups using sodium hydroxide is used for the preparation of modified chitin, which is called chitosan. 

Chitin, obtained mainly from the cuticle of the marine crustacean, is presently of considerable interest in industrial and medical fields,i 2 since it is a mucopolysaccharide which resembles cellulose structurally and is present in nature as much as cellulose. Deacetylation of the acetamide group at the 2-position in the acetylglucosamine unit of chitin by alkaline hydrolysis yields chitosan, a cationic polyelectrolyte. Chitosan appears more useful than chitin, having both hydroxyl and amino groups which can be modified easily. Therefore, these chitin and chitosan derivatives are finding a broad range of applications. 

Cellulose/ chitosan Obtained by electrospinning and alkaline hydrolysis of cellulose acetate and dibutyryl chitin. [180]... 

The most important derivative of chitin is chitosan obtained by partial deacetylation of chitin in the solid state under alkaline conditions or by enzymatic hydrolysis in the presence of a chitin deacetylase. The ratio of 2-acetamido-2-deoxy-D-glucopyranose to 2-amino-2-deoxy-D-glucopyra-nose moieties determines the identity of the product, that is, chitin or chitosan [9]. The published methods used for the production of chitosan from chitin are summarized in Table 2.3. 

Chitin is a stable compoimd, incompatible with oxidizing agents [59]. In the solid state imder alkaline condition (e.g., NaOH, KOH, heat at about 120 °C) or by enzymatic hydrolysis in the presence of a chitin deacetylase, it hydrolyses to form the deacetylated degradation product chitosan [6,7,10,11]. It was found that the presence of urea in basic media and at low temperature (—20 °C) had little effect on chitin structure and that urea is of benefit to the stability of chitin solution [38]. 

The most important chitin derivative is chitosan, obtained by its partial deacetylation under alkaline conditions or by enzymatic hydrolysis in the presence of chitin deacetylase. Because of the semicrystalline morphology of chitin, chitosan obtained by a solid-state reaction has a heterogeneous distribution of acetyl groups along the chain. On the other hand when chitin is treated with concentrated aqueous sodium hydroxide, N-deacetylation proceeds smoothly and homogeneously deacetylated samples are obtained [37]. 

Chitin is insoluble in water and barely soluble in acidic media (forming ammonium salts). Heating in acid or alkahne solutions leads to the hydrolysis of bound N-acetyl-n-glucosamine with the formation of n-glucosamine and acetic acid. Heating under acidic conditions causes partial depolymerisation of chitin through the hydrolysis of P-glycosidic bonds. In alkaline solutions, depolymerisation occurs to a lesser extent. 

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