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Syntheses of imidazolium‐bridged cyclodextrin dimers and their catalytic properties in the hydrolytic cleavage of p ‐nitrophenyl alkanoates
Author(s) -
Luo MeiMing,
Xie RuGang,
Yuan DeQi,
Lu Wei,
Xia PingFang,
Zhao HuaMing
Publication year - 1999
Publication title -
chinese journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 1001-604X
DOI - 10.1002/cjoc.19990170411
Subject(s) - chemistry , hydrolysis , selectivity , catalysis , cleavage (geology) , benzene , cyclodextrin , medicinal chemistry , dissociation constant , dissociation (chemistry) , reaction rate constant , stereochemistry , kinetics , organic chemistry , biochemistry , physics , receptor , geotechnical engineering , quantum mechanics , fracture (geology) , engineering
Two imidazolium‐bridged cyclodextrin dimers 3a and 3b were prepared by reacting 6‐deoxy‐6‐ N ‐imidazolyl‐β‐CD (2) with bis(bromomethyl) benzene. The catalytic properties of 2, 3a and 3b in the hydrolytic cleavage of p ‐nitrophenyl alkanoates, in the form of acetate (PNPA), butanoate (PNPB), hexanoate (WH) and octanoate ( PNPO), were examined. CD dimers showed middling rate enhancements around neutrality. Catalytic rate constants ( k c ) in the presence of 3a or 3b did not vary much with chain length of esters. In contrast, dissociation constants ( K d ) and selectivity factors ( k c / K d ) for “long‐chain” esters were much smaller and significantly larger than those for “short‐chain” ones respectively, indicating CD dimers 3a and 3b have good dimensional recognition ability and substrate selectivity in the hydrolytic cleavage of p ‐nitrophenyl alkanoate. Their kinetic consequences are briefly interpreted.