A reproducible method for obtaining water-soluble chitin and a relationship between solubility and degree of deacetylation of chitin were studied. It was found that the regenerated chitin isolated at low temperature from an alkali chitin solution left at 25 "C for 48 to 77 h showed very good solubility in water at 0°C. The degree of deacetylation of an alkaline treated chitin was determined by titration with hydrochloric acid. It increased rapidly to about 75% as the alkaline treatment time increased and began to level off to about 90%, and only the regenerated chitin samples with around 50% of deacetylation were found to be soluble in water. The X-ray diffraction diagrams showed that these were amorphous, although both chitin with lower degree of deacetylation and chitosan had crystallinity. The improved solubility of chitin with about 50% of deacetylation would be attributed to the partial deacetylation which probably brought about the destruction of secondary structure and also the increase of the hydrophilic property on account of the increased number of amino groups. ZUSAM MENFASSUNG : Es wurden eine reproduzierbare Methode zur Darstellung wasserloslichen Chitins und eine Beziehung zwischen Loslichkeit und Entacetylierungsgrad des Chitins untersucht. Dabei wurde gefunden, daB regeneriertes Chitin, das bei niedriger Temperatur aus einer Alkali-Chitin-Losung isoliert wurde, welche 48 bis 77 h bei 25 "C stehen gelassen wurde, eine sehr gute Loslichkeit in Wasser bei 0°C zeigte. Der Entacetylierungsgrad eines mit Alkali behandelten Chitins wurde durch Titration mit Salzsaure bestimmt. Dieser wuchs mit zunehmender Alkali-Behandlungszeit rasch bis ca. 75 % an, um dann langsam bei ca. 90% abzuflachen, wobei nur die Proben des regenerierten Chitins mit etwa 50 % Entacetylierung in Wasser loslich erschienen. Diese waren, wie Rontgenbeugungsdia-*) Part I : cf."). als auch Chitosan Kristallinitat aufwiesen. Die verbesserte Loslichkeit des Chitins mit ca. 50% Entacetylierung ist wohl auf die partielle Entacetylierung zuriickzufiihren, durch die wahrscheinlich eine Zerstorung der Sekundarstruktur bewirkt wurde, und auf die Zunahme des hydrophilen Charakters durch die erhohte Zahl an Aminogruppen.

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Chitin was deacetylated by heterogeneous and homogeneous alkaline hydrolyses. In the heterogeneous hydrolysis, upper limits in the degree of deacetylation were found to exist at low reaction temperatures. The products obtained were all insoluble in water and those with a degree of deacetylation up to 80% retained some crystallinity. These results seemed to indicate that the deacetylation under the heterogeneous conditions proceeded preferentially in the amorphous region to give block-type copolymers of N-acetyl-D-glucosamine and D-glucosamine units. In the homogeneous hydrolysis, on the other hand, all the products with a degree of deacetylation of ca. 50% were found to be soluble in water independent of the hydrolysis temperature. The crystallinity of the products decreased much more rapidly and samples with a degree of deacetylation >40% were amorphous. These results suggested that the deacetylation under homogeneous conditions proceeded randomly to give the random-type copolymers of the two units. This randomness was concluded to have brought about the interesting water-solubility of products with a degree of deacetylation of ca. 50%.

The solution polycondensation of 3,3′ ‐diaminobenzidine tetrahydrochloride with aromatic dicarboxylic acid derivatives in polyphosphoric acid was found to give high molecular weight polyphenylenebenzimidazoles easily. Their preparation and physical properties, such as thermal stability, solubility, crystallinity, are described.

SynopsisThe adsorption abilities of chitin and its congeners with two series of degrees of deacetylation prepared by two different deacetylation procedures were compared. Among the polysaccharides obtained by the heterogeneous method, those with higher amino group content had higher adsorption ability. Plots of collection percentages versus amino group content, however, did not give straight lines. The plot for the chelation on the congeners that were prepared by homogeneous hydrolysis had a maximum at about 50% amino group content, and the value was higher than that for the sample with the highest amino group content, which was prepared by heterogeneous hydrolysis. These results suggest that the polysaccharides with about 50% amino group content obtained by the homogeneous procedure are potentially useful for the removal of metals.