A practical and efficient epoxidation of aromatic olefins using Oxone in a two-phase system (ethyl acetate-water) is described. The reported method is suitable for large-scale synthesis and does not require phase transfer catalyst (PTC) or pH control.
Dioxiranes are highly clean and powerful oxidants and have been applied to a variety of oxidations.1 Recently Shi and co-workers reported a new method for epoxidation using trifluoroacetone in aqueous acetonitrile as solvent and hydrogen peroxide in place of Oxone (potassium peroxomonosulphate) generally used as dioxiranes generator. Though this method is practical and does not need large amounts of potassium carbonate to neutralize the consequently formed potassium hydrogen sulfate, several problematic features are still evident from the standpoint of large-scale manufactureability. For example, aqueous acetonitrile generally does not readily dissolve aromatic olefins due to their poor solubilities. A more fundamental problem is that toxic and rather expensive acetonitrile is unavoidable as an oxidizing mediator to ensure high conversion. Recycling of acetonitrile is also difficult mainly due to boiling point which is almost the same as that of water. In the last two decades, two-phase systems have been investigated in order to overcome these problems. These procedures in general used n-Bu4NHSO4 as the phase transfer catalyst (PTC). As a result, a tedious dropwise addition of base solution over a long time period under strict pH control was needed to avoid the oxidation of the PTC. From environmental and economical viewpoints, we sought a more practical and efficient procedure using an alternative solvent.
Reference
Org. Proc. Res. Dev., 6 (4), 405 -406, 2002. (https://www.thevespiary.org/rhodium/Rhodium/pdf/two-phase.oxone.epoxidation.pdf)
(https://www.thevespiary.org/rhodium/Rhodium/pdf/two-phase.oxone.epoxidation.pdf)