Fine-Bubble–Slug-Flow Hydrogenation of Multiple Bonds and Phenols

Abstract

We describe a promising method for the continuous hydrogenation of alkenes or alkynes by using a newly developed fine-bubble generator. The fine-bubble-containing slug-flow system was up to 1.4 times more efficient than a conventional slug-flow method. When applied in the hydrogenation of phenols to the corresponding cyclohexanones, the fine bubble–slug-flow method suppressed over-reduction. As this method does not require the use of excess gas, it is expected to be widely applicable in improving the efficiency of gas-mediated flow reactions.

Key words

flow reaction - gas–liquid reaction - hydrogenation - alkynes - alkenes - phenols

Publication History

Received: 27 August 2020

Accepted after revision: 16 September 2020

Article published online:
21 October 2020

• References and Notes


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• 15 Hydrogenation of Alkenes or Alkynes by the H₂-FB-Slug-Flow Method: Typical Procedure A 500 mL Duran bottle was charged with a solution of the appropriate substrate 1 (8.28 mmol) in MeOH (400 mL). The reactor was charged with 10% Pd/C (1.1 g, 0.47 mmol) and placed in a column oven (CTO-10AC; Shimadzu, Japan) at 60 °C. The solution of 1 was delivered at a flow rate of 2.0 mL/min (residence time in the reactor = 35 s), and H₂ gas was delivered at a flow rate of 1.0 mL/min (1 equiv). The pressure in the front of the reactor was set to approximately 4 MPa to generate FBs. After 30 min of operation at 60 °C, the reaction mixture was collected every 10 min and analyzed by GC-FID, without purification.