MULTIPLE PATHWAYS IN CYCLODEXTRIN-CATALYZED HYDROLYSIS OF PERFLUOROALKYLAMIDES

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