Monitoring chemical reactions by low‐field benchtop NMR at 45 MHz: pros and cons

Monitoring chemical reactions is the key to controlling chemical processes where NMR can provide support. High‐field NMR gives detailed structural information on chemical compounds and reactions; however, it is expensive and complex to operate. Conversely, low‐field NMR instruments are simple and relatively inexpensive alternatives. While low‐field NMR does not provide the detailed information as the high‐field instruments as a result of their smaller chemical shift dispersion and the complex secondary coupling, it remains of practical value as a process analytical technology (PAT) tool and is complimentary to other established methods, such as ReactIR and Raman spectroscopy. We have tested a picoSpin‐45 (currently under ThermoFisher Scientific) benchtop NMR instrument to monitor three types of reactions by 1D 1 H NMR: a Fischer esterification, a Suzuki cross‐coupling, and the formation of an oxime. The Fischer esterification is a relatively simple reaction run at high concentration and served as proof of concept. The Suzuki coupling is an example of a more complex, commonly used reaction involving overlapping signals. Finally, the oxime formation involved a reaction in two phases that cannot be monitored by other PAT tools. Here, we discuss the pros and cons of monitoring these reactions at a low‐field of 45 MHz by 1D 1 H NMR. Copyright © 2015 John Wiley & Sons, Ltd.