New catalysts for Baeyer-Villiger oxidation reactions

Kazuaki Ishihara and his group at Nagoya University (Japan; www.ishihara-lab.net) have established a new, environment friendly reaction technology — using Baeyer-Villiger oxidations — for selectively oxidizing ketones into esters. The reaction uses hydrogen peroxide as the oxidant, and has potential as a safer alternative to the conventional industrial route for making the nylon precursor epsilon-caprolactam from epsilon-caprolactone. Instead of H2O2, industrial routes have used acetyl hydroperoxide for making epsilon-caprolactam, which required very careful handling of explosive acetyl hydroperoxide, and also purification steps for removing byproducts and the corrosive, smelly residual catalyst after the reaction. The new route uses hydrogen peroxide with an effective oxidation-acceleration catalyst system, both of which are easier to handle, and no byproducts are produced. The researchers found that two environmentally friendly catalysts — lithium tetrakis(pentafluorophenyl)borate or Li[B(C6F5)4], and calcium tetrakis(pentafluorophenyl) or Ca[B(C6F5)4] — can be used in both hydrophilic systems with H2O2 as the oxidant, and in lipophilic systems, including those with ketone substrates and ester products. These…