Baeyer-Villiger Oxidation of Cyclic Ketones Catalyzed by Amino Acid Ionic Liquids

A series of amino-acid-based ionic liquids was synthesized via one-step protonation of the corresponding L -amino acid by utilizing an array of proton sources. The catalytic activity of the amino-acid-based ionic liquids for the Baeyer-Villiger oxidation of cyclic ketones was investigated using cyclopentanone as a model cycloketone. The proline-based ionic liquid [ProH]CF 3 SO 3 was shown to exhibit the best catalytic activity. The reaction condition was optimized to give the following reagent ratio of n (cyclopentanone): n (catalyst): n (H 2 O 2 )=1:0.06:4, 60 °C and 6 h. Under the optimum conditions, the conversion of cyclopentanone was 96.57% and the selectivity for δ-valerolactone was 73.01%. The catalytic activity was shown to be constant after 4 cycles. A simple treatment was allowed for the recover and the reuse of [ProH]CF 3 SO 3 . The successful utilization of [ProH]CF 3 SO 3 to catalyze a host of cyclic ketones via Baeyer-Villiger oxidation clearly demonstrated the capacity of [ProH]CF 3 SO 3 to tolerate variation in the substrate.