- Effects of charge separation, effective concentration, and aggregate formation on the phase transfer catalyzed alkylation of phenol
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The factors that influence the rate of alkylation of phenol under phase transfer catalysis (PTC) have been investigated in detail. Six linear, symmetrical tetraalkylammonium cations, Me4N+, Et 4N+, (n-Pr)4N+, (n-Bu) 4N+, (n-Hex)4N+, and (n-Oct) 4N+, were examined to compare the effects of cationic radius and lipophilicity on the rate of alkylation. Tetraalkylammonium phenoxide·phenol salts were prepared, and their intrinsic reactivity was determined from initial alkylation rates with n-butyl bromide in homogeneous solution. The catalytic activity of the same tetraalkylammonium phenoxides was determined under PTC conditions (under an extraction mechanism) employing quaternary ammonium bromide catalysts. In homogeneous solution the range in reactivity was small (6.8-fold) for Me4N+ to (n-Oct) 4N+. In contrast, under PTC conditions a larger range in reactivity was observed (663-fold). The effective concentration of the tetraalkylammonium phenoxides in the organic phase was identified as the primary factor influencing catalyst activity. Additionally, titration of active phenoxide in the organic phase confirmed the presence of both phenol and potassium phenoxide aggregates with (n-Bu)4N+, (n-Hex)4N+, and (n-Oct)4N+, each with a unique aggregate stoichiometry. The aggregate stoichiometry did not affect the PTC initial alkylation rates.
- Denmark, Scott E.,Weintraub, Robert C.,Gould, Nathan D.
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supporting information; experimental part
p. 13415 - 13429
(2012/09/25)
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- Interaction between methanol and the Cl-, Br-, I-, NO3-, ClO4-, BF4-, SO3CF3- and PF6- anions studied by FTIR spectroscopy
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The interaction between methanol and the Cl-, Br-, I-, NO3-, ClO4-, BF4-, SO3CF3- and PF6- anions in dilute dichloromethane solutions has been investigated. The OH stretching vibration was used to monitor the hydrogen bonds formed between the anions and the methanol molecules, providing a direct measure of the hydrogen-bond strength. Concentrations of free and anionbonded methanol molecules were measured and the equilibrium constants calculated. The wavenumber shift and the free energy of hydrogen-bond formation was found to be significantly correlated. For the anions studied it was found that the hydrogen-bond strength increases in the order: PF6- 4- 4- 3CF3- 3- - -. Acta Chemica Scandinavica 1997.
- Kristiansson, Olof,Schuisky, Mikael
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p. 270 - 273
(2007/10/03)
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