15589-78-3Relevant academic research and scientific papers
Chemical shifts of phenolic monomers in solution and implications for addition and self-condensation
Haupt, Robert A.,Renneckar, Scott
, p. 95 - 101 (2013/03/14)
Alkali metal counter-cations alter the electron density of phenolates in solution by electrostatic interactions. This change in electron density affects their reactivity toward formaldehyde, hydroxymethylphenols, and isocyanates during polymerization. The electronic perturbation of phenolic model compounds in the presence of alkali metal hydroxides was investigated with 13C and 1H nuclear magnetic resonance in polar solvents relative to non-ionic controls, altering the chemical shifts of the model compounds, thus indicating changes in electron density using the chemical shift as a proxy. These shifts were attributed to Coulombic electrostatic interactions of the counter-cation with the phenolate anion that correlated to hydrated ionic radius and solvent dielectric constants. The predicted relative reaction rates for formaldehyde addition based on electron density ranking from 13C nuclear magnetic resonance of the phenolic models was compared with the literature values. Predictions for condensation reactions of 2- and 4-hydroxymethylphenol from chemical shifts were consistent with published results. The results permit predictions for the reaction of phenolic compounds for the formation of thermosetting polymeric materials. Copyright
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.
