The Stereoselective Retardation of the Alkaline Hydrolysis of Organic Esters by Binuclear Cu(II) Complexes with Cyclodextrins

Article abstract of DOI:10.1246/bcsj.58.1658

The alkaline hydrolysis of p-nitrophenyl acetate (p-NPA) in 1.0 mol dm^-3 NaOH at 25 deg C was almost completely retarded by the addition of a binuclear Cu(II) complex with α-cyclodextrin Cu2α-CD).The dissociation constant for an inclusion complex of Cu2α-CD with p-NPA was determined to be 0.059 mmol dm^-3, which is about one 200th that for an inclusion complex of α-CD with p-NPA.The alkaline hydrolysis of o- and m-nitrophenyl acetates was also retarded by Cu2α-CD, though the extent of retardation was much less than that for p-NPA.A binuclear Cu(II) complex with β-cyclodextrin (Cu2β-CD) also caused a stereoselective deceleration of the alkaline hydrolysis of the esters.However, the stereoselectivity of Cu2β-CD was not so remarkable as that of Cu2α-CD.Dissociation constants for inclusion complexes of Cu2α-CD with several alcohols and other organic substrates were determined by the kinetic examination of the competitive inhibition effect of the substrates on the association of Cu2α-CD with p-NPA.Cu2α-CD formed stable inclusion complexes with such disk-like molecules as cyclohexanol, cycloheptanol, and p-nitrobenzyl alcohol.The geometry of a Cu2α-CD-p-NPA inclusion complex was presumed on the basis of these results.