Catalysis by Cyclodextrins in Nucleophilic Aromatic Substitution Reactions II. Amines as Nucleophiles

MONICA BARRA; RITA H. DE ROSSI; ELBA I. BUJÁN

AMER CHEMICAL SOC

Lugar: Washington; Año: 1987 vol. 52 p. 5004 - 5004

he kinetics of the reactions of 1-chloro-2,4-dinitrobenzen and 1-fluoro-2,4-dinitrobenzene with piperidine, butylamine, and morpholine in the presence of β-cyclodextrin( CD) was studied. There is an increase in the observed rate constant for the reactions of the first two amines at pH < pKAH when CD is added, but there is no change in rate for these two reactions at pH > pKAH and for the reaction of morpholine either at pH < pKAH or at pH > pKAH. The three amines (A) as well as their conjugated acids (AH) form inclusion complexes with the CD. The association equilibrium constants for the amines are 50, 3, and 17 M-1 for piperidine, butylamine, and morpholine, respectively. Part of the observed catalysis is attributed to the fact that the amines and the complexed amines (ACD) react with the substrate at similar rates and at constant pH, the ratio (A + ACD)/(AH + AHCD) increases with the concentration of CD. Besides that, the complexed substrates react with the complexed amines a