Electrospray ionization mass spectrometry (ESI-MS) is a soft ionization technique commonly coupled with liquid or gas chromatography for the identification of compounds in a one-time view of a mixture (for example, the resulting mixture generated by a synthesis). Over the past decade, Scott McIndoe and his research group at the University of Victoria have developed various methodologies to enhance the ability of ESI-MS to continuously monitor catalytic reactions as they proceed. The power, sensitivity and large dynamic range of ESI-MS have allowed for the refinement of several homogenous catalytic mechanisms and could potentially be applied to a wide range of reactions (catalytic or otherwise) for the determination of their mechanistic pathways. In this special feature article, some of the key challenges encountered and the adaptations employed to counter them are briefly reviewed.

Alkyl substitution α to the ketone of an allenyl vinyl ketone enhances Nazarov reactivity by inhibiting alternative pathways involving the allene moiety and through electron donation and/or steric hindrance. This substitution pattern also accelerates Nazarov cyclisation by increasing the population of the reactive conformer and by stabilising the oxyallyl cation intermediate. Furthermore, α substitution by an alkyl group does not alter the regioselectivity of interrupted Nazarov reactions when the oxyallyl cation intermediate is intercepted by addition of an oxygen nucleophile, or by [4+3] cyclisation with acyclic dienes. The regioselectivity of the Nazarov process for allenyl vinyl ketones was determined to be a result of an electronic bias in the oxyallyl cation intermediate. Computational data are consistent with this observation.

Dynamic information can be obtained on in-progress reactions in real time using a balloon-pressurized Schlenk flask in combination with an electrospray ionization mass spectrometer. The apparatus can be set up on a Schlenk line or in a glovebox and transported to the spectrometer, to be initiated by addition of catalyst or reactant by syringe through a septum. The system is demonstrated on palladium-catalyzed oxidation of phosphines.

Red cabbage (Brassica oleracea) contains anthocyanins that dissolve in water, have antioxidant properties, and have a fairly wide range of color changes owing to changing pH. These characteristics not only make red cabbage useful as an acid–base indicator for pH demonstrations in the classroom but can also be made into a visually dynamic, color-changing, hypotonic “sports drink” that is safe to consume at the end of the experiment. When combined with readily available kitchen ingredients, this experiment is inexpensive, visually compelling, and easily scaled up to allow classroom participation.

The conjugate addition of an alcohol to a butynoate ester using an organophosphine catalyst was monitored using pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS), together with 31 P and 1 H NMR spectroscopy. The combination of methods allowed examination of the reaction progress from the perspective of reactants and products ( 1 H NMR) and insights into behaviors of the reaction intermediates and formation of byproducts ( 31 P NMR and MS). The resulting traces could be closely approximated through numerical modeling by appropriate selection of rate constants, and a sound understanding of the mechanism and the means by which oligomeric byproducts are formed allows a rational approach to experimental design. Scheme 1 A selection of phosphine-mediated addition reactions.Scheme 2 Iterative use of a phosphine-mediated addition, leading to an oligo-vinyl ether intermediate that can be used for a variety of subsequent applications. PaperNJC