Jason P. Hallett

Esterification in ionic liquids: The influence of solvent basicity

The second-order rate constant (k2) for the esterification of methoxyacetic acid with benzyl alcohol is reported in a range of ionic and molecular solvents. The solvent effects on esterification rate are examined by using a linear solvation energy relationship based on the Kamlet-Taft solvent scales (alpha, beta, and pi*). It is shown that the hydrogen bond basicity of the solvent is the dominant parameter in determining the esterification rate and that the best rates are achieved in low basicity solvents.

A spectroscopic and computational exploration of the cybotactic region of gas-expanded liquids: methanol and acetone.

Local compositions in supercritical and near-critial fluids may differ substantially from bulk compositions, and such differences have important effects on spectroscopic observations, phase equilibria, and chemical kinetics. Here, we compare such determinations around a solute probe dissolved in CO2-expanded methanol and acetone at 25 degrees C from solvatochromic experiments with molecular dynamics simulations. UV/vis and steady-state fluorescence measurements of the dye Coumarin 153 in the expanded liquid phase indicate preferential solvation in both the S0 and S1 states by the organic species. Simple dielectric continuum models are used to estimate local compositions from the spectroscopic data and are compared to molecular dynamics simulations of a single C153 molecule dissolved in the liquid phase at bubble point conditions. The simulations provide information about the local solvent structure around C153. They suggest the presence of large solvent clustering near the electron-withdrawing side of the probe. Preferential solvation exists in both the S0 and S1 states, but a large disagreement between simulation and experiment exists in the S1 state. Potential reasons for this disparity are discussed.

Use and recovery of a homogeneous catalyst with carbon dioxide as a solubility switch

A method for fluorous biphasic catalysis is described,in which the fluorous liquid is replaced by fluorinated silica, the fluorous catalyst is induced to dissolve in the organic solvent by the presence of CO2, and the recovery of the catalyst after the reaction is achieved by release of the CO2 pressure.