An alternative means of epoxidation is reported that uses environmentally benign supercritical carbon dioxide as both a solvent and reactant in combination with aqueous H2O2, which is made possible through the in situ formation of peroxycarbonic acid. Experiments were conducted at 40 °C and 120 bar in which cyclohexene was epoxidized to 1,2-cyclohexene oxide and 1,2-cyclohexanediol in this aqueous−organic biphasic system. Through the addition of NaHCO3 and the hydrophilic cosolvent dimethylformamide, the conversion increased from 0.4 mol % (without additives) to 12.6 mol % (with 0.1 mol % NaHCO3 and 13 mol % dimethylformamide). The results suggest that the reaction occurs within the aqueous phase, which led to investigations using the water-soluble olefin 3-cyclohexen-1-carboxylate sodium salt as a means of verifying the reaction location. Epoxidation of 3-cyclohexen-1-carboxylate sodium salt went to completion in less than 20 h at 40 °C and 120 bar with an epoxide yield of 89 mol % and diol yield of 11 mol %.

This work reports the first studies designed to examine the detailed mechanism of a phase-transfer catalyzed reaction between a supercritical CO2 phase and a solid salt phase. The nucleophilic displacement of benzyl chloride with potassium cyanide to form phenylacetonitrile and potassium chloride was carried out with a tetraheptylammonium salt as the phase-transfer catalyst. The effects of various reaction variables on the kinetics were investigated, including the amount of catalyst, the amount of potassium cyanide, the presence of acetone cosolvent, and temperature. The kinetic data, along with catalyst solubility measurements, indicate that the operating reaction mechanism is a three-phase system consisting of a supercritical CO2 phase, a catalyst-rich phase, and a solid salt phase and that the reaction actually occurs in the catalyst-rich phase. Further, the reaction mechanism was investigated with two additional phase-transfer catalysts, 18-crown-6 and poly(ethylene glycol), and these results are consistent with the postulated three-phase mechanism.

We report the selective removal of a desired reaction intermediate with a supercritical fluid in a new synthesis route to poly(ethylene terephthalate), avoiding ethylene glycol. We have successfully catalyzed the esterification of terephthalic acid with ethylene oxide in a supercritical fluid with a series of quaternary ammonium salts to form mono(2-hydroxyethyl terephthalate). This desired monoester was removed from the involatile bed of terephthalic acid and catalyst by continuous extraction with supercritical fluid before subsequent reaction to the diester could take place.

The first example of a phase-transfer-catalyzed alkylation reaction under supercritical fluid conditions is reported. The reaction is that of phenylacetonitrile and ethyl bromide in the presence of tetrabutylammonium bromide and potassium carbonate in supercritical ethane at 45, 60, and 75 °C and 138 bar. Results show that the reaction will go to completion in less than 24 h in the presence of the catalyst but that only a few percent conversion is achieved without it during the same period of time. The effects of catalyst concentration, temperature, and cosolvents are investigated. Catalyst solubility estimates and kinetic analyses suggest that the reaction takes place on the surface of the potassium carbonate particles. When the same reaction is attempted in supercritical carbon dioxide, both carboxylation and alkylation are observed. Cycloalkylation reactions between phenylacetonitrile and dibromoalkanes are also discussed.

No abstract