Selective Reduction of Ketones and Aldehydes in Continuous-Flow Microreactor—Kinetic Studies

Abstract

Abstract:In this work, the kinetics of Meerwein-Ponndorf-Verley chemoselective reduction of carbonyl compounds was studied in monolithic continuous-flow microreactors. To the best of our knowledge, this is the first report on the MPV reaction kinetics performed in a flow process. The microreactors are a very attractive alternative to the batch reactors conventionally used in this process. The proposed micro-flow system for synthesis of unsaturated secondary alcohols proved to be very efficient and easily controlled. The microreactors had reactive cores made of zirconium-functionalized silica monoliths of excellent catalytic properties and flow characteristics. The catalytic experiments were carried out with the use of 2-butanol as a hydrogen donor. Herein, we present the kinetic parameters of cyclohexanone reduction in a flow reactor and data on the reaction rate for several important ketones and aldehydes. The lack of diffusion constraints in the microreactors was demonstrated. Our results were compared with those from other authors and demonstrate the great potential of microreactor applications in fine chemical and complex intermediate manufacturing.

Catalytic Functionalized Structured Monolithic Micro-/Mesoreactors: Engineering, Properties, and Performance in Flow Synthesis: An Overview and Guidelines

“…The recent study of the MPV reduction of a number of aldehydes and ketones, with 2-butanol in 0.14Zr-Pr-MMRs with the M1 structure, showed that its kinetics can be quantified by the first-order kinetics equation (Ciemięga et al, 2018;. First, preliminary experiments performed using reactors 10-80 mm of length (4.5 mm dia., velocities varying from 2 to 16 mm/min) clearly proved the lack of external mass transport limitation of reaction kinetics (Maresz et al, 2018). The temperature dependence of the reaction rate allowed for the estimation of the activation energy for the reduction of hexanone as equal to 52 kJ/mol and the frequency factor k 2.69 1/min.…”

“…The performance of MMRs doped with various Lewis acid centers has been extensively studied in the chemoselective Meerwein-Ponndorf-Verley (MPV) reduction of carbonyl compounds-a widespread route for the synthesis of unsaturated secondary alcohols, and the results have been presented in a series of articles (Koreniuk et al, 2015a;Ciemięga et al, 2017b;Ciemięga et al, 2018;Maresz et al, 2018;. Preliminary studies showed that modification of silica monoliths (M1 structure) with zirconium (IV) propoxide (Zr-Pr-MMR) resulted in the formation of zirconium complexes with mixed propoxy/hydroxyl ligands bound to the silica surface, which were much more catalytically active than silica-supported zirconia (Zr-MMR) (Koreniuk et al, 2015a).…”

Metal-doped mesoporous ZrO2catalyzed chemoselective synthesis of allylic alcohols from Meerwein–Ponndorf–Verley reduction of α,β-unsaturated aldehydes

“…3 The high-pressure involved in such a chemical process requires expensive equipment and an elaborate experimental set-up with associated safety risks. 4,5 The problems associated with these classical methods could be avoided in the Meerwein-Ponndorf-Verley (MPV) reduction.…”

Catalytic Methods in Flow Chemistry

“…All the prepared materials were successfully employed, under flow conditions, for the hydrogenation of methyl levulinate using 2-propanol as the hydrogen donor. Better performance was observed with catalysts possessing higher dispersion of ZrO 2 particles.Monolithic flow microreactors were employed for studying the kinetics of the Meerwein-Ponndorf-Verley reduction of carbonyl compounds [5]. Zirconium-functionalized silica monoliths constituted the core of the reactor and performed well in promoting the reduction of cyclohexanone and other ketones and aldehydes using 2-butanol as the hydrogen donor.…”

“…Monolithic flow microreactors were employed for studying the kinetics of the Meerwein-Ponndorf-Verley reduction of carbonyl compounds [5]. Zirconium-functionalized silica monoliths constituted the core of the reactor and performed well in promoting the reduction of cyclohexanone and other ketones and aldehydes using 2-butanol as the hydrogen donor.…”