Hydrolytic cleavage of p-nitrophenyl alkanoates in aqueous solutions of cyclodextrins

Abstract

The hydrolytic cleavage of p-nitrophenyl alkanoates has been investigated in moderately alkaline aqueous solutions of α- and β-cyclodextrins. The catalytic effects of cyclodextrins (the k_c/k_un ratios) first decrease and then increase with increasing chain length. Such a trend is apparently related to the mode of insertion of the alkanoates into the cyclodextrin. Induced c.d. measurements indicate that only in the case of short-chain alkanoates (up to butyrate or hexanoate) the p-nitrophenyl moiety is included in the cyclodextrin cavity whereas for long-chain esters the hydrocarbon chain is inserted into it. The kinetic consequences of the dual mode of complexation and differences between the two types of cyclodextrins investigated are briefly discussed.