Rates of intramolecular cyclisations of o-(3-halopropyloxy)phenoxide ion [(1a,b), halogen = Br or I, respectively] increase with decreasing solvent polarity in the order H2O < MeOH < EtOH < PriOH < MeCN, except that reaction of (1a) is faster in H2O than in MeOH, and in H2O (1a) is more reactive than (1b). These effects depend upon the solvation of the oxide ion and the leaving halide ion in the transition state, and relative reactivities kI/kBr indicate the relative importance of these interactions. Micelles of CTAX [C16H33NMe3X, X = Br, Cl, NO3, OH, OTs, or (SO4)0.5] increase the rates by factors of ca. 2 for (1a) and by 4 for (1b), with little effect by the counter-ion. Rate enhancements and kI/kBr increase sharply in the sequence of surfactant head groups N+Me3 < N+Et3 < N+Pr3 < N+Bu3. Increasing the size of the n-alkyl group apparently decreases hydration of the aryloxide without destabilising the transition state. These micellar medium effects can be related to medium effects in intermolecular reactions in micelles.
SOLVENT AND MICELLAR EFFECTS UPON THE CYCLISATION OF O-3-HALOPROPYLOXYPHENOXIDE IONS
GERMANI, Raimondo;SAVELLI, Gianfranco;
1989
Abstract
Rates of intramolecular cyclisations of o-(3-halopropyloxy)phenoxide ion [(1a,b), halogen = Br or I, respectively] increase with decreasing solvent polarity in the order H2O < MeOH < EtOH < PriOH < MeCN, except that reaction of (1a) is faster in H2O than in MeOH, and in H2O (1a) is more reactive than (1b). These effects depend upon the solvation of the oxide ion and the leaving halide ion in the transition state, and relative reactivities kI/kBr indicate the relative importance of these interactions. Micelles of CTAX [C16H33NMe3X, X = Br, Cl, NO3, OH, OTs, or (SO4)0.5] increase the rates by factors of ca. 2 for (1a) and by 4 for (1b), with little effect by the counter-ion. Rate enhancements and kI/kBr increase sharply in the sequence of surfactant head groups N+Me3 < N+Et3 < N+Pr3 < N+Bu3. Increasing the size of the n-alkyl group apparently decreases hydration of the aryloxide without destabilising the transition state. These micellar medium effects can be related to medium effects in intermolecular reactions in micelles.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
