Esterification of beta-chitin via intercalation by carboxylic anhydrides.
beta-chitin is known to form intercalation complexes with aliphatic alcohols and amines. We found that it also forms complexes with carboxylic anhydrides. When the beta-chitin-acetic anhydride complex was heated to 105 degrees C, the hydroxyl groups of chitin were acetylated by a host-guest reaction, maintaining the host's crystal structure. Structures of complex and acetylated products were analyzed by X-ray diffraction, (13)C CP/MAS NMR, and infrared spectroscopy. The maximum degree of substitution (DS) was close to 1.0, suggesting regioselective esterification at the C6 position of chitin. Partially acetylated beta-chitin with a DS of 0.4 could incorporate various guest species that are difficult to be incorporated by original beta-chitin. In contrast, beta-chitin acetate with a DS of 1 lost the ability to form a complex. Intercalation complexes of beta-chitin with cyclic anhydrides (succinic and maleic) also underwent esterification by heating, and the products with a DS of approximately 1 dissolved in aqueous alkali, apparently as the result of the dissociation of introduced carboxyl groups. These phenomena are potentially useful in controlling the complexation ability of beta-chitin and the preparation of regioselectively esterified chitin derivatives.
Yoshifuji
A
A
Department of Biomaterials Science, Graduate School of Agricultural & Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
Noishiki
Y
Y
Wada
M
M
Heux
L
L
Kuga
S
S
D000085:Acetates / Q000737:chemistry; D000089:Acetic Anhydrides / Q000737:chemistry; D000812:Anhydrides / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry*; D001704:Biopolymers / Q000737:chemistry*; D002686:Chitin / Q000737:chemistry*; D048271:Chitosan; D017377:Diatoms / Q000378:metabolism; D004951:Esterification; D006358:Hot Temperature; D009682:Magnetic Resonance Spectroscopy; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
D000085:Acetates; D000089:Acetic Anhydrides; D000812:Anhydrides; D001672:Biocompatible Materials; D001704:Biopolymers; D002686:Chitin; C031800:acetic anhydride; D048271:Chitosan