Application of Cryptand/Polystyrene Drift‐Type Phase Transfer Catalysts for Reduction of Ketones

Abstract

A drift-type phase transfer catalyst, cryptand-22, adsorbed on poly(styrene/diviny benzene)-sulfonic resin was prepared and applied to catalyze the reduction of ketones, e.g,, acetophenone, benzophenone and benzaldehyde with NaSH, as a reducing agent, Before the reaction, cryptand-22 was adsorbed on the SUIfonic resin wilh ion-pairing, resin-S03-'NH-cryptand-22, The ion-pairs can be destroyed by adjusting the basicity of the reaction solution with NaOH and h e cryptand can be released from the resin into the reaction solution as a homogeneous catalyst during the reaction period. After the reaction, tbe cryptand catalyst can be readsorbed on the resin by adjusting the acidity of the solution with HCI and can be readily recovered by filtration like a heterogeneous catalyst. The draft-type cryptand catalyst exhibited better catalytic ability than some common crown ethers, e.g., 15-crown-5, benzo-15-crown-5, 12-crown-4 and dibenzo-18-crown-6 for the reduction of acetophenone wilh NaBH,. Effects of solvents, pH of solutions, concenuation of the catalyst, reducing agents and resin properly on the reduction of ketones were investigated and discussed.The reaction mechanism of the cryptand catalyzed reduction was also studied.

[3.2.1] and [4.1.1] isomers of Lehn's [2.2.2] Cryptand: Prediction of ion selectivity by quantum chemical calculations XV**

“…This discovery granted Lehn together with Pedersen and Cram a Nobel Prize in 1987, [3] and to the field of supramolecular encapsulation chemistry the legacy to pursuit for optimizing and better understanding of the systems that represent it. Today some of these compounds have found their application in numerous fields, such as: phase-transfer catalysis, [4] selective complexation of radioactive or toxic ions in medicine, [5] studies on Zintl phases, [6] models for carrier-antibiotics such as Valinomycin and enzyme inhibitors, [7] and as a ligand for MRI contrast agents. [8] The unmatched selectivity of Lehn-type diaza-polyether cryptands for encapsulation of complementary sized metal cations guests [9] are attributed to great thermodynamic and kinetic stabilities.…”

Host-Guest Complexes of Two Isomeric 2,2’-Bioxazole Based {2}-Lehn-Type Cryptands. Prediction of Ion Selectivity by Quantum Chemical Calculations. Part XIV

“…[2,3] The potential of similar cage like compounds to selectively bind guests was recognized immediately. Those first publications paved a way for the development of more complex and refined structures of such cage like systems; some of them currently have potential applications in a selective complexation of radioactive or toxic ions in medicine, [4] in analysis [5] as a ligand for MRI contrast agents, [6] in catalysis [7] or in elementary research, [8] and as model compounds, e.g. for valinomycin and enzyme inhibitors.…”