Flash Organometallic Catalysis Uncovered by Continuous Microfluidic Devices

The flash organometallic catalysis is a new concept that refers to the study of fast and controlled organometallic catalytic reactions by using microfluidic devices. Flash reactions' kinetics (ms-s scale) is often ignored due to the lack of proper research tool in organometallic chemistry. The development of microfluidic systems offers the opportunity to discover under-studied mechanisms and new reactions. In this concept, the basic theory of kinetic measurement in a microreactor is briefly reviewed and then two examples on studying flash organometallic catalytic transformation are introduced. One example is the discovery of a highly active palladium catalytic species for Suzuki Coupling and the other example is the study of a neglected isomerization catalytic cycle with a time scale of seconds before isomerization-hydroformylation by customized microfluidic devices. The last part is summary and prospect of this new area. Customizing a microfluidic device with good engineering design for a target reaction supports flash reactions' kinetic experimentation and could become a general strategy in chemistry lab.

A spectIR-fluidic reactor for monitoring fast chemical reaction kinetics with on-chip attenuated total reflection Fourier transform infrared spectroscopy

Microfluidics has emerged as a powerful technology with diverse applications in microbiology, medicine, chemistry, and physics. While its potential for controlling and studying chemical reactions is well recognized, the extraction and analysis of useful chemical information generated within microfluidic devices remain challenging. This is mainly due to the limited tools available for in situ measurements of chemical reactions. In this study, we present a proof-of-concept spectIR-fluidic reactor design that combines microfluidics with Fourier transform infrared (FTIR) spectroscopy for in situ kinetic studies of fast reactions. By integrating a multi-ridge silicon attenuated total reflection (ATR) wafer into the microfluidic device, we enable multi-point measurements for precise reaction time monitoring. As such, this work establishes a validated foundation for studying fast chemical reactions using on-chip ATR-FTIR spectroscopy in a microfluidic reactor environment, which enables simultaneous monitoring of reagents, intermediates, and products using a phosphate proton transfer reaction. The spectIR-fluidic reactor platform offers customizable designs, allowing for the investigation of reactions with various time scales, and has the potential to significantly advance studies exploring reaction mechanisms and optimization.

Efficient degassing and ppm-level oxygen monitoring flow chemistry system

Low oxygen levels are critical for a long range of chemical transformations carried out in both flow and batch chemistry. Here, we present an inline continuous flow degassing system based on a gas-permeable membrane inside a vacuum chamber for achieving and monitoring ppm-level oxygen concentrations in solutions. The oxygen presence was monitored with a molecular oxygen probe and a continuously running UV-vis spectrometer. An automated setup for discovering optimal reaction conditions for minimal oxygen presence was devised. The parameters tested were: flow rate, vacuum pressure, solvent back-pressure, tube material, tube length and solvent oxygen solubility. The inline degassing system was proven to be effective in removing up to 99.9% of ambient oxygen from solvents at a flow rate of 300 μl min^-1 and 4 mbar vacuum pressure inside the degassing chamber. Reaching lower oxygen concentrations was limited by gas permeation in the tubing following the degassing unit, which could be addressed by purging large volume flow reactors with an inert gas after degassing or by using tubing with lower gas permeability, such as stainless steel tubing. Among all factors, oxygen solubility in solvents was found to play a significant role in achieving efficient degassing of solvents. The data presented here can be used to choose optimal experimental parameters for oxygen-sensitive reactions in flow chemistry reaction setups. The data were also fitted to an analytically derived model from simple differential equations in physical context of the experiment.

An Automated Computer-Vision "Bubble-Counting" Technique to Characterise CO2 Dissolution into an Acetonitrile Flow Stream in a Teflon AF-2400 Tube-in-Tube Flow Device

A Teflon AF-2400 based tube-in-tube device was used to generate flow streams of CO₂ in acetonitrile and a computer-vision based 'bubble counting' technique was used to estimate the amount of CO₂ that had passed into solution whilst in the tube-in-tube device by quantifying the amount of CO₂ that left solution (forming separate gas-phase segments) downstream of the back-pressure regulator. For both CO₂ pressures used, there appeared to be a minimum residence time below which no CO₂ was observed to leave solution. This was assumed to be due to residual CO₂ below (or close to) the saturation concentration at atmospheric pressure and, by taking this into account, we were able to fit curves corresponding to simple gradient-driven diffusion and which closely matched previously obtained colorimetric titration data for the same system. The estimated value for the residual concentration of CO₂ (0.37 M) is higher than, but in reasonable general correspondence with, saturation concentrations previously reported for CO₂ in acetonitrile (0.27 M).

Revisiting aromatic diazotization and aryl diazonium salts in continuous flow: highlighted research during 2001–2021

Aryl diazonium salts play an important role in chemical transformations; however their explosive nature limits their applications in batch.

Modern advancements in continuous-flow aided kinetic analysis

Although kinetic analysis has traditionally been conducted in a batch vessel, continuous-flow aided kinetic analysis continues to swell in popularity.

Copper/TEMPO-catalyzed continuous aerobic alcohol oxidation in a micro-packed bed reactor

A micro-packed bed reactor has been developed to demonstrate aerobic oxidation of alcohols to aldehydes, utilizing green oxidant O2 and effective Cu/TEMPO-catalyzed system.

Design and testing of an ozonolysis reactor module with on-the-fly ozone degassing under flow conditions

Ozonolysis is an attractive, efficient, and green means of introducing oxygen containing functionalities using only oxygen and electricity.

Liquid-phase catalytic hydrodechlorination of chlorinated organic compounds in a continuous flow micro-packed bed reactor over a Pd/AC catalyst

A continuous flow system based on a micro-packed bed reactor was developed for hydrodechlorination, and the hydrogenation of chlorobenzene was selected as the model reaction. With the optimal reaction conditions, a conversion and selectivity of 100% were obtained.

Advanced Real-Time Process Analytics for Multistep Synthesis in Continuous Flow*

In multistep continuous flow chemistry, studying complex reaction mixtures in real time is a significant challenge, but provides an opportunity to enhance reaction understanding and control. We report the integration of four complementary process analytical technology tools (NMR, UV/Vis, IR and UHPLC) in the multistep synthesis of an active pharmaceutical ingredient, mesalazine. This synthetic route exploits flow processing for nitration, high temperature hydrolysis and hydrogenation reactions, as well as three inline separations. Advanced data analysis models were developed (indirect hard modeling, deep learning and partial least squares regression), to quantify the desired products, intermediates and impurities in real time, at multiple points along the synthetic pathway. The capabilities of the system have been demonstrated by operating both steady state and dynamic experiments and represents a significant step forward in data-driven continuous flow synthesis.