Reaction characterization by flow NMR: quantitation and monitoring of dissolved H₂via flow NMR at high pressure

Abstract

This communication describes an in situ method for direct observation and quantitation of dissolved H2 at high pressure with concurrent monitoring and characterization of organic reactions. This capability also allows for direct measurement of k(L)a values and provides insight into reactions that was not previously attainable.

Insight into catalyst speciation and hydrogen co-evolution during enantioselective formic acid-driven transfer hydrogenation with bifunctional ruthenium complexes from multi-technique operando reaction monitoring

“…Inspection of the 1 H NMR data revealed a signicant amount of H 2 appearing at 4.56 ppm in the early stages of the reaction ( Fig. 5; the concentration of dissolved H 2 is in agreement with previous 1 H FlowNMR studies 20 ).…”

Practical aspects of real-time reaction monitoring using multi-nuclear high resolution FlowNMR spectroscopy

“…On-line NMR reaction monitoring may be performed either with continuous flow, where data is acquired whilst the sample is moving through the receiver coil, or with a pulsed flow, where the flow is halted during measurement. Most on-line-NMR reaction monitoring systems use continuous flow 3,10,11,21,30 as this means that the sample within the spectrometer is continually refreshed to ensure that the volume measured is always representative of the mixture within the reaction vessel; however, pulsed systems have been developed for use with some low field spectrometers where continuous flow is not possible. 32 For all on-line NMR reaction monitoring setups there is an inherent time required for the sample to be pumped from the reaction vessel to the spectrometer, leading to a slight delay between a change occurring in the reaction vessel and detection.…”

“…A recent study by Foley et al clearly demonstrates the significance of mass transfer limitations when using static NMR tubes for reaction monitoring, leading to strikingly different kinetic results for the same reaction when monitored by different NMR techniques. 2 An alternative to these established techniques is the growing field of on-line NMR monitoring, which is amenable to a wide range of reaction conditions including reactions requiring heating, cooling and inert or reactive gas atmospheres, [3][4][5] and in principle can circumvent the above limitations. Performing the reaction outside of the spectrometer allows reagents to be added without stopping data acquisition and the reaction to be properly mixed to ensure that the reaction kinetics measured are not obscured by diffusional effects.…”

A High‐Pressure NMR Probe for Aqueous Geochemistry

“…At ambient conditions, NMR spectroscopy has emerged as a powerful analytical technique to monitor chemical processes within the environment. [12] Furthermore, advancements in high-resolution, high-pressure probe design [13][14][15] have not only allowed for the study of geochemical reaction dynamics, [16][17][18] but also the pressure dependencies of critical micelle concentrations, [19] dissolved gas formation from catalytic reactions, [20] as well as several studies probing protein folding, aggregation, and stabilization of rare highenergy states. [21][22][23][24] Despite the tremendous scientific advancement from these studies, the current NMR probe designs cannot fully accommodate both high pressures and highresolution molecular-level data needed to begin to evaluate the geochemical models.…”