The atmospheric pressure Meerwein reaction

Area of Science:

• Analytical Chemistry
• Organic Chemistry
• Mass Spectrometry

Background:

• The gas-phase Meerwein reaction of (thio)acylium ions is a valuable tool for class-selective screening of cyclic (thio)epoxides.
• Previous studies demonstrated the generality and utility of this reaction under in-vacuum conditions.

Purpose of the Study:

• To report the efficient performance of the gas-phase Meerwein reaction at atmospheric pressure.
• To expand the applicability of the gas-phase Meerwein reaction to a wider range of molecules.
• To investigate the reaction under electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) conditions.

Main Methods:

• Performed the gas-phase Meerwein reaction at atmospheric pressure using ESI and APCI.
• Utilized tetramethylurea (TMU) and (thio)TMU as dopants, co-injected with solutions of (thio)epoxides in various solvents.
• Employed on-line collision-induced dissociation (CID) of Meerwein products for enhanced structural characterization.

Main Results:

• The gas-phase Meerwein reaction was successfully performed efficiently at atmospheric pressure under both ESI and APCI.
• A variety of cyclic (thio)epoxides, including phenyl epoxide, thiirane, and propylene oxide, reacted effectively.
• Protonated (thio)TMU readily dissociated to form reactive (thio)acylium ions, facilitating the Meerwein reaction.
• Competitive reactions between (thio)acylium ions and TMU or (thio)epoxides were observed.
• On-line CID of Meerwein products enhanced selectivity for structural characterization, especially for complex (thio)epoxides.

Conclusions:

• The gas-phase Meerwein reaction can be efficiently conducted at atmospheric pressure using ESI and APCI, broadening its applicability.
• This atmospheric pressure method expands the range of molecules amenable to gas-phase Meerwein reaction analysis.
• The use of CID enhances the utility of the reaction for structural elucidation and screening of (thio)epoxides.