Fluorescence on the Flow: Continuous Xanthene Dye Synthesis from Gallic Acid in a Coiled Flow Inverter

Transparent coiled flow inverters (CFIs) are employed for real-time monitoring of gallic acid condensation. Tailored-made CFI provides desired residence time for carrying out reactions at high flow rate. Optimal conditions (190 °C, 5 mL h⁻¹, 4.46 W m⁻² ) maximize the yield of the green-fluorescent product xanthene analogue, establishing CFIs as versatile, cost-effective tools for continuous flow synthesis.

Transparent coiled flow inverters (CFI), which are superior to opaque coil reactors, are hardly explored in performing condensation reactions of organic molecules. Herein, the continuous flow condensation reaction of gallic acid using CFI is reported with a 4 mm internal diameter. The length of the flow reactor is varied by connecting CFIs in series. Real-time images of reactor captured during flow synthesis resolve the intricacies of reaction dynamics and stages of desired product formation. Stack CFI provides a desired residence time for carrying out reaction at high flow rate. Condensation of gallic acid in dimethyl formamide yields a green emissive xanthene analog. The production of organic emitter is optimized by regulating reactant flow rate and temperature of the reaction. The presence of a vapour–liquid phase boundary enhances the interfacial area, that further contributes to increasing the product yield. The optimized condition for fluorescent product using stack CFI is 190 °C (±5) temperature at 5 mL h⁻¹ (±0.5) flow rate. A residence time of about 14 h (±1) and a heat flux of 4.46 W m⁻² (±0.5) are desired for maximizing product yield using stack CFI. These suggest that CFI-based flow reactor can easily be tailor-made and economical as well.

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