2. CHITIN AND MUCOSUBSTANCES
109
be remembered that chitin, particularly after alkaline treatment, is a
powerful absorbent of organic substances as well as inorganic ones. Use
of this property of chitin has been made for chromatographic analytical
purposes (107).
1. Chemical Hydrolysis of Chitin
The course of degradation of chitin by mineral acids gives a variety
of products, depending on the concentration of acid employed and the
time and temperature of the hydrolysis. Under vigorous conditions (e.g.,
6 N-hydrochloric acid at 100° for 12 hours), extensive hydrolysis to
D-glucosamine (2-amino-2-deoxy-D-glucose) occurs, with some decomposition of the amino sugar. It was by such degradation that this sugar
was first shown (108) to be present in the polymer, though its exact
structure was not established until 1939, when it was synthesized by an
unequivocal route by Haworth et al. (109). The amino sugar had already
been synthesized earlier (110), though not in such a manner as to leave
its configuration beyond doubt. In the hydrolysis, cleavage of N-acyl
groups occurs (111); it was shown by Brach (112) that acetic acid and
amino sugar were formed in equimolar quantities. It is not entirely clear,
however, that acetyl groups are the sole amino substituents, and investigation by more accurate, modern methods seems desirable.
In an extensive study, Hackman (113) showed that at 20° chitin from
Jasus verreauxi Η. M. Edw. (prepared by washing in dilute acid and
alkali) underwent extensive degradation in ION hydrochloric acid,
21 N-sulfuric acid, or 85% phosphoric acid, most of the degradation occurring in the first few minutes and leading to partly deacetylated oligosaccharides and to N-acetyl glucosamine. The free sugar was present
only in traces. In 2 Ν hydrochloric acid little hydrolysis occurs at 25°,
but at 100° in 24 hours considerable amounts of glucosamine and oligosaccharides are formed (see Fig. 13).
Under milder conditions of acidic hydrolysis (114) (e.g., IN hydrochloric acid at 100° for 1 hour) glycosidic bonds are cleaved preferentially (62), and the principal product is thus N-acetyl-D-glucosamine.
Hackman (115) has reported that in 2 Ν hydrochloric acid at 100°, 6.6%
conversion of chitin to the amino sugar hydrochloride takes place in
7 hours.
By means of carefully controlled conditions (116), oligosaccharides
have been obtained from chitin which have been of considerable importance in the study of its molecular structure. Acetolysis represents
one of the early methods used in such an approach, and gave small yields
of a fully acetylated derivative of the disaccharide chitobiose (di-N-
109
be remembered that chitin, particularly after alkaline treatment, is a
powerful absorbent of organic substances as well as inorganic ones. Use
of this property of chitin has been made for chromatographic analytical
purposes (107).
1. Chemical Hydrolysis of Chitin
The course of degradation of chitin by mineral acids gives a variety
of products, depending on the concentration of acid employed and the
time and temperature of the hydrolysis. Under vigorous conditions (e.g.,
6 N-hydrochloric acid at 100° for 12 hours), extensive hydrolysis to
D-glucosamine (2-amino-2-deoxy-D-glucose) occurs, with some decomposition of the amino sugar. It was by such degradation that this sugar
was first shown (108) to be present in the polymer, though its exact
structure was not established until 1939, when it was synthesized by an
unequivocal route by Haworth et al. (109). The amino sugar had already
been synthesized earlier (110), though not in such a manner as to leave
its configuration beyond doubt. In the hydrolysis, cleavage of N-acyl
groups occurs (111); it was shown by Brach (112) that acetic acid and
amino sugar were formed in equimolar quantities. It is not entirely clear,
however, that acetyl groups are the sole amino substituents, and investigation by more accurate, modern methods seems desirable.
In an extensive study, Hackman (113) showed that at 20° chitin from
Jasus verreauxi Η. M. Edw. (prepared by washing in dilute acid and
alkali) underwent extensive degradation in ION hydrochloric acid,
21 N-sulfuric acid, or 85% phosphoric acid, most of the degradation occurring in the first few minutes and leading to partly deacetylated oligosaccharides and to N-acetyl glucosamine. The free sugar was present
only in traces. In 2 Ν hydrochloric acid little hydrolysis occurs at 25°,
but at 100° in 24 hours considerable amounts of glucosamine and oligosaccharides are formed (see Fig. 13).
Under milder conditions of acidic hydrolysis (114) (e.g., IN hydrochloric acid at 100° for 1 hour) glycosidic bonds are cleaved preferentially (62), and the principal product is thus N-acetyl-D-glucosamine.
Hackman (115) has reported that in 2 Ν hydrochloric acid at 100°, 6.6%
conversion of chitin to the amino sugar hydrochloride takes place in
7 hours.
By means of carefully controlled conditions (116), oligosaccharides
have been obtained from chitin which have been of considerable importance in the study of its molecular structure. Acetolysis represents
one of the early methods used in such an approach, and gave small yields
of a fully acetylated derivative of the disaccharide chitobiose (di-N-