Continuous-flow technologies make it possible to carry out chemical reactions in a continuously moving stream rather than processing raw materials in separate batches. This allows process conditions, such as reagent molar ratios, temperature, and reaction time, to be controlled more precisely. Researchers from the Research Group of Microreactors, together with their collaborators, investigated whether TAP—an important intermediate in the synthesis of trazodone, a drug widely used to treat depression and insomnia—could be prepared in a flow reactor.
The reaction step under investigation was N-alkylation, in which a carbon chain is attached to a nitrogen atom. As the reaction medium, the team designed a new system consisting of two immiscible liquid phases—an aqueous phase and an organic phase. The reaction between them is enabled by a phase-transfer catalyst, which, in simplified terms, acts as a “carrier” transporting reacting species between two environments that normally mix only to a very limited extent.
The researchers examined how the conversion of the starting material, product yield, and reaction selectivity were affected by temperature, the time the mixture spent flowing through the reactor, and the concentrations of the individual components. Based on the experiments, they optimized the reaction conditions, described the reaction kinetics, and proposed mechanisms for the processes occurring in both solid–liquid and liquid–liquid systems.
An important finding was that the application of ultrasound made it possible to substantially increase the yield of the continuous synthesis. The study also demonstrates that transferring a chemical reaction from batch to continuous operation is not simply a matter of changing the equipment, but may require a fundamental redesign of the entire reaction system. The new ultrasound-assisted liquid–liquid approach represents an important step towards more controllable and efficient continuous processes for the preparation of pharmaceutical intermediates.
- Jaklová N., Stavárek P., Salmi T., Eränen K., Klusoň P.: Continuous-Flow Phase-Transfer-Catalyzed N-Alkylation for Trazodone Synthesis: Development and Optimization. ACS Eng. Au 2026, 6(3), 415–426. doi.org/10.1021/acsengineeringau.5c00111