Palladium-catalyzed amination reactions in flow: overcoming the challenges of clogging via acoustic irradiation

Abstract

A continuous-flow palladium-catalyzed amination reaction was made possible through efficient handling of solids via acoustic irradiation. Various diarylamines were obtained with reaction times ranging from 20 s to 10 min.

Solvent-free semihydrogenation of acetylene alcohols in a capillary reactor coated with a Pd–Bi/TiO 2 catalyst

“…Although microreactors have demonstrated great promise in many organic liquid-phase reactions, application of heterogeneous catalysts for gas-liquid reactions still remains a major challenge [19,[27][28][29]. For example, hydrogenation reactions require an efficient handling of (i) hydrogen gas, (ii) liquid substrate medium, and (iii) solid catalyst to ensure quick mass transfer and reaction rates.…”

Flow Technology for Organometallic-Mediated Synthesis

“…A similar microfluidic device able to perform the palladiumcatalyzed C-N cross-coupling reactions has been assembled as shown in Scheme 56 [79]. The main feature of the apparatus includes an acoustic irradiation system that allows for handling solid byproducts formed in the palladium-catalyzed amination reaction.…”

Particle Handling Techniques in Microchemical Processes

“…Secondary forces, also significant when a concentrated system of particles scatters acoustic standing waves, have been described in a more detailed review [22]. Acoustic waveforms in the range of kHz, for example ultrasonic cleaning equipment, have been demonstrated as effective in carrying out microchemical transformations that generate solids [15,35,64]. On-chip ultrasound has been engineered to manage the NaCl formation during palladium-catalyzed bond forming reactions [13].…”

“…If the thermodynamics predict reactive particle formation, then nucleation theory is the appropriate starting point to understand how to control particles in microfluidics [15,[34][35][36]70]. The solubility product of each compound should be estimated for a given reaction solvent and the corresponding supersaturation ratio, the driving force for nucleation, approximated.…”