Pressure Stabilization and Solvation Thermodynamics of a Hemiketal Reaction Intermediate

This work reports the first pressure stabilization of a hemiketal intermediate, 2-methoxy-2 propanol, formed in the reaction of acetone and methanol, observed using Raman spectroscopy. Acetone dissolved in methanol is found to undergo a two-step reaction, with the ketal 2,2-dimethoxy-propane as the final product and the hemiketal observed as an intermediate. In a more dilute stoichiometric mixture of acetone and methanol in liquid tetrahydrofuran (THF), quantitative formation of the hemiketal is observed at pressures above 2 GPa. The complete set of reaction thermodynamic functions (Δ H °, Δ V °, Δ S °, Δ G °, Δ U °, Δ A °) is obtained for the hemiketal formation reaction in THF as a function of temperature and pressure and compared with previous measurements of Δ H °, Δ S °, and Δ G ° for acetone dissolved in methanol. Comparisons with quantum calculations for the isolated reactant and product species are used to completely quantitate the effects of solvation on the hemiketal formation reaction.