Large amounts of waste may result from the neutralization of homogeneous acid catalysts following reaction. Here we present examples of in situ acid formation and self-neutralization, thus eliminating waste and offering advantages for product recovery. The formation of a-terpineol (2) from b-pinene (1) is a reaction of commercial significance that is typically run with strong acid. We demonstrate that the reaction can be performed under more environmentally benign conditions using the in situ acid formation capabilities of two different green technologies: CO 2 expanded liquids and reactions in hot water (200 °C). This work presents an example of the application of these methods to a reaction that has commercial significance and adds to our knowledge about the benefits and effects of co-solvents. The relative rates and product distributions achieved in each system are presented and discussed.
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
%.
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