Multiple pathways in cyclodextrin-catalyzed hydrolysis of perfluoroalkylamides

Article abstract of DOI:10.1021/ja00118a005

The hydrolysis of p-nitroanilide of perfluoroalkanoic acids, CF₃(CF₂)_nCO^-, with n = 1, 2, 3, 5, 6, and 7, 1a-f, was studied in the presence of β-cyclodextrin (CD). All reactions were catalyzed by CD through the formation of a 1:1 and 1:2 inclusion complexes. The association equilibrium constants for the 1:1 complexes were dependent on the number of carbons of the fluoroalkyl chain, whereas those of the 1:2 complexes were almost independent. These results indicate that, in the former case, the perfluoroalkyl chain is included, while in the latter, the CD unit encloses the aryl ring. For compounds 1a,b both complexes were more reactive than the substrate itself. The ratio of the reaction of complexed to uncomplexed substrate had its highest value for 1a in the case of the 1:1 complex, and for 1b, the 1:2 complex. This is attributed to the geometry of the complexes. Although compounds 1c-e reacted at the same rates in the free or 1:1 complexed form, CD accelerated the reactions because of an increase of the pK_a of the substrate, which results in a higher concentration of the neutral reactive substrate at the same pH. Compound 1f formed aggregates even at 10^-6 M concentration, and CD-induced deaggregation resulted in catalysis of the reaction.