On‐Line Reaction Monitoring and Mechanistic Studies by Mass Spectrometry: Negishi Cross‐Coupling, Hydrogenolysis, and Reductive Amination

Abstract

Reaction monitoring using inductive ESI mass spectrometry allows chemical reactions to be tracked in real time, including air- and moisture-sensitive as well as heterogeneous reactions. Highly concentrated solutions can also be monitored for long periods without emitter clogging. Sheath gas assists in nebulization and a sample splitter reduces the delay time and minimizes contamination of the instrument. Short-lived intermediates (ca. 5 s) were observed in Pd/C-catalyzed hydrogenolysis, and several intermediates were seen in Negishi cross-coupling reactions.

Biogenic aldehyde determination by reactive paper spray ionization mass spectrometry

“…Some information on the kinetics of these experiments was obtained by shortening the reaction time from 5 min to 1 min but this did not show any effect on the relative intensity of the iminium ion peaks. In fact the reaction occurs in the charged microdroplets generated by paper spray ionization [42][43][44][45][46] as demonstrated by mixing formaldehyde and the amine and immediately recording the mass spectrum. The resulting mass spectrum was identical to that shown in Fig.…”

Mechanistic and Kinetic Study of Singlet O2 Oxidation of Methionine by On-Line Electrospray Ionization Mass Spectrometry

“…To the best of our knowledge, most on-line ESI MS approaches sampled reaction solution at a pressure near atmospheric or higher, where the solution was delivered to ESI by gravity or positive gas pressure [45][46][47][48][49][50][51]. However, our reaction system needs to be maintained at a pressure of 25 τ as rationalized above.…”

“…Note that a typical flow rate for ESI is 1 μL/min, which would result in far too long delay for kinetic measurements if this rate is used for sample transfer. In a previous on-line ESI MS experiment [52], we adopted Cooks and coworkers' method [51] by adding a splitter to the sample transfer line, right before ESI. The sample was swept to ESI under N 2 gas pressure.…”

State-of-the-art mass spectrometry for point-of-care and other applications: A hands-on intensive short course for undergraduate students

“…Reaction acceleration, which has been a topic of two recent reviews, 29-30 and on-line reaction monitoring [31][32] were explored by students via the Katritsky transamination reaction (Figure 4a). 33 The Leidenfrost phenomenon 6 was first explained: a reaction mixture is deposited onto a surface heated significantly above the liquid's boiling point so that evaporating vapor forms a thermally insulating layer on which droplets of the reaction mixture are levitated.…”