83897-41-0Relevant academic research and scientific papers
Alkali and alkaline-earth metal ion catalysis in the reaction of aryl acetates with methoxide ion. Effect of a poly(oxyethylene) side arm
Ercolani,Mandolini
, p. 423 - 427 (2007/10/02)
The effect of added alkali (Na, K) and alkaline-earth (Sr, Ba) metal bromides on the rate of acyl transfer from o-acetoxyphenyl 3,6,9,12-tetraoxatridecyl ether (2) to methoxide ion in methanol at 25 °C has been investigated spectrophotometrically. All of the added salts increased significantly the rate of reaction in the order Na+ + 2+ 2+, a maximum catalytic effect of nearly 102 being observed with the latter metal ion. A proper analysis of rate data afforded equilibrium constants for associations of metal ions with reactants and transition state, showing that in all cases the transition state binds metal ions much more strongly than the reactants. An analogous set of rate measurements was carried out for comparison purposes on the corresponding reaction of phenyl acetate (1). The fact that catalytic effects are much greater with 2 than with 1 reveals that a substantial contribution to the stability of the transition state of the metal ion assisted path arises from interaction of the metal ion with the oxygen donors of the side arm.
Template Effects. 4. Ion Pairing of Aryloxide Ions with Alkali Cations in 99percent Me2SO: Influence on the Rate of Formation of Benzo-18-crown-6 and of Other Williamson-Type Reactions
Illuminati, Gabriello,Mandolini, Luigi,Masci, Bernardo
, p. 555 - 563 (2007/10/02)
The effect of alkali metal ions on the rate of formation of benzo-18-crown-6 in 99percent Me2SO by cyclization of the conjugate base of o-hydroxyphenyl 3,6,9,12-tetraoxa-14-bromotetradecyl ether has been quantitatively accounted for according to a scheme involving separate contributions from free (ki) and cation-paired (kip) phenoxide ion.The study has included several additional intra- and intermolecular alkylations of phenoxide ions as reference reactions to provide a set of 25 equilibrium constants for the association of five different phenoxides with the five alkali cations.Both Coulombic interaction and coordination with the neutral oxygen donors are important in determining ion pair stability, but the order in all cases is dominated by Coulombic interaction.This suggests contact interaction in the phenoxide-cation pairs, which is also consistent with evidence from the UV spectra.Whereas the rate of formation of B18C6 is depressed by Li+ (kip/ki + (kip/ki = 100).In contrast, in the reference reactions the ion pairs with the alkali are either negligibly reactive or much less reactive than the free anions.The association constants of the alkali cations with B18C6 have been determined under the same conditions.A comparative analysis of the extent of interaction of the cations with the reactant, transition state, and reaction product of the crown ether forming reaction shows that the transition state binds cations more strongly than the reactant or reaction product and reveals that cation interaction with both the negative charge and the neutral donors bear significant contribution to the stability of the ion pair transition state.A rationale for the template effect is presented in terms of proximity effects and chemical effects arising from interaction of the cation with the nucleophilic site of the reactant.
