Phase Behavior of the Reactants, Products and Catalysts Involved in the Allylic Epoxidation of trans-2-Hexen-1-ol to (2R,3R)-(+)-3-Propyloxiranemethanol in High Pressure Carbon Dioxide


B. A. Stradi, J. P. Kohn, M. A. Stadtherr, and J. F. Brennecke


The possible phase behavior of a reaction mixture is an important consideration when evaluating CO2 as an alternative solvent to replace traditional organic compounds. To address this issue we present phase equilibrium measurements and modeling of primarily binary mixtures with CO2 of the reactants, products and catalysts present in the allylic epoxidation of trans-2-hexen-1-ol to (2R,3R)-(+)-3-propyloxiranemethanol. This reaction occurs with very high enantiomeric selectivity in liquid CO2, yields a high value product, and would normally be carried out in an organic solvent like benzene. Thus, it is a promising candidate for CO2 solvent replacement. The systems studied are trans-2-hexen-1-ol-CO2, tert-butyl hydroperoxide (in decane)-CO2, (2R,3R)-(+)-3-propyloxiranemethanol-CO2, tert-butyl alcohol-CO2, diisopropyl L-tartrate-CO2, vanadium(V)tri-i-propoxy oxide-CO2 and titanium(IV) isopropoxide-CO2. The compositions of the liquid phases were determined as a function of pressure, at temperatures between 303.15 and 323.15 K and pressures between 31.5 and 110.2 bar. Liquid/liquid immiscibility regions were found for the trans-2-hexen-1-ol-CO2 and (2R,3R)-(+)-3-propyloxiranemethanol-CO2 binaries. This region is located between 310.9 K (the lower critical end point) and 315.3 K (a type-k point) and the corresponding pressures of 79.5 and 86.7 bar for trans-2-hexen-1-ol-CO2. The (2R,3R)-(+)-3-propyloxiranemethanol-CO2 liquid/liquid immiscibility region ranges from 315.1 K (a type-k point) to below 293.7 K, at the corresponding pressures of 86.1 to 55.8 bar. All of the other binaries exhibited simple vapor/liquid equilibrium (VLE). Modeling with the Peng-Robinson equation of state (PREOS) gave reasonably good results for the two phase regions for all of the systems, using just one temperature-independent parameter for each binary system. The PREOS did predict LLV three phase regions for the trans-2-hexen-1-ol-CO2 and (2R,3R)-(+)-3-propyloxiranemethanol-CO2 binaries, but generally at conditions different from those observed experimentally. Finally, we present some preliminary predictions of the multicomponent phase equilibria based on the binary measurements and models.

J. Supercriical Fluids, 12, 109-122 (1998)

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