Laser Organic Synthesis of Trichloromethyl Radicals/Ions and Study of Subsequent Reactions by Droplet Mass Spectrometry

Abstract

In this study, we used atmospheric-pressure droplet laser-ablation mass spectrometry to elucidate the chemical pathways induced by UV-laser irradiation of carbon tetrachloride (CCl4) droplets containing various alcohols. We focused on the reaction dynamics following the laser-induced generation of trichloromethyl radicals (CCl3) and ions (CCl3+) in the microdroplets. Mass spectrometric analysis revealed that CCl3+ initiated sequential substitution reactions. With phenol, sequential substitution occurred, resulting in the formation of mono-, di-, and trisubstituted ions. Conversely, methanol and ethanol exclusively yielded trisubstituted species [C(OR)3+], regardless of the concentration, which we attributed to the formation of alcohol aggregates in the CCl4 solution. For bulkier alcohols, steric hindrance suppressed substitution, and this favored CCl3-mediated hydrogen abstraction followed by radical coupling. Isotope-labeling experiments with ethanol revealed a higher abundance of coupling products derived from beta-site abstraction than from alpha-site abstraction, suggesting distinct kinetic preferences in the coupling step. These findings demonstrate that the microdroplet environment and molecular aggregation dictate the selectivity of laser-induced organic synthesis. This knowledge provides a basis for developing novel pulsed-laser-based synthetic methodologies.