A High Mobility Reactor Unit for R&D Continuous Flow Transfer Hydrogenations

Abstract

A suitcase sized mobile reactor unit (MRU) weighing in at less than 10 kg was designed for laboratory scale transfer hydrogenations in continuous flow. Simple cyclohexene and a cosolvent in combination with a palladium-on-charcoal packed bed reactor provided a setup with isolation of nearly all products without the need for further purification. Several functional groups including olefins, triple bonds, nitro-groups, carbonyls, and so forth were effectively reduced with retention times as low as 2 min. Additionally, standard protection groups such as Cbz, benzyl, and allyl ether or esters were removed in high yields. To prove the flexibility of the setup an example of the Mizoroki−Heck reaction was also performed on the MRU. Finally, two scale-up transfer hydrogenation experiments were performed affording isolation of the desired target compounds in 0.5 and 0.8 mol scales with less than 4 h of continuous operation on the MRU.

Chemoselective Continuous Ru-Catalyzed Hydrogen-Transfer Oppenauer-Type Oxidation of Secondary Alcohols

“…Hydrogen transfer methods constitute an attractive approach for many synthetic transformations. − Among these, reduction processes are more well-established. − Hydrogen transfer oxidation methods have also evolved, with the development of new catalysts, employing aqueous media, supported catalysts and in the absence of hydrogen acceptors. − Most notably, Bäckvall’s group has implemented procedures for hydrogen transfer oxidation employing commercial catalysts, and a base, to achieve high yields, and with good functional group compatibility. , …”

Chiral auxiliary recycling in continuous flow: automated recovery and reuse of Oppolzer's sultam

“…The hydrogenation was next investigated using a packed bed reactor of Pd/C. 18 Full conversion ( t res ≈ 1 min) was initially achieved but catalyst deactivation prevented long term operation. Hypothesizing that basic impurities were at fault, 19 a co-feed of 0.1% (v/v) aqueous acetic acid was incorporated in combination with an increase of the reactor temperature to 45 °C.…”

Continuous flow (micro-)reactors for heterogeneously catalyzed reactions: Main design and modelling issues

“…Hydrogen transfer reduction reactions have been tested by using a Pd/C catalyst [77]. This avoids the presence of H2 tanks to the in situ generation of gaseous hydrogen, which anyway results in a multiphase system.…”