The cleavage of aspirin by α- and β-cyclodextrins in basic aqueous solution

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Abstract
The deacetylation of aspirin is promoted by α- and β-cyclodextrins (αCD and βCD) in basic aqueous solution. From saturation kinetics the dissociation constants (Kd) for the aspirin anion – CD complexes are 12 mM (αCD) and 20 mM (βCD). At pH 12.25 the limiting rate constant for ester cleavage is 14 times (αCD) and 7 times (βCD) that in the medium alone. For the 4-chloroaspirin anion (Kd = 3.8 mM) the cleavage induced by αCD is 240 times that in the medium, but 5-chloroaspirin shows a very small effect. The results are discussed in terms of a model derived from that of Bender and co-workers (1967) and are compared to earlier work. For the αCD anion, the 4-chloroaspirin anion is almost as good as "substrate" as m-chloro-and m-tert-butylphenyl acetates. Compared to hydroxide ion, the αCD anion is better at cleaving 4-chloroaspirin (2000×) and aspirin (36×).

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