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

• Published in: Magnetic resonance in chemistry 2016-06, Vol.54 (6), p.437-443
• Main Authors: Silva Elipe, Maria Victoria, Milburn, Robert R
• Format: Article
• Language: English
• Subjects: Chemical reactions; Cross coupling; Esterification; Formations; Monitoring; Monitors; Nuclear magnetic resonance; Oximes
• ISSN: 0749-1581; 1097-458X
• DOI: 10.1002/mrc.4189

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 1H 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 45MHz by 1D 1H NMR. Copyright © 2015 John Wiley & Sons, Ltd.