Continuous Flow Synthesis of DABCYL Azo Fluorescent Quenchers

A robust and inherently safer continuous flow process has been developed for the synthesis of DABCYL azo fluorescent quenchers. The conventional diazotization azo coupling sequence was successfully translated from hazardous batch conditions to a controlled multistep flow process, enabling the in situ generation and immediate consumption of reactive diazonium intermediates. Systematic optimization of temperature and residence time afforded yields up to 84% and throughputs of 17 g h–1 in single-step operation. The integrated two-step continuous system delivered DABCYL 3a in up to 84% yield with a throughput exceeding 65 g h–1 and excellent reproducibility. All DABCYL derivatives exhibited broad visible absorption (418–532 nm) and high molar extinction coefficients (2.4–3.3 × 104 M–1 cm–1), confirming their suitability as dark quenchers. The process demonstrates enhanced safety and throughput, providing a practical foundation for the potential development of industrial-scale manufacture of specialty DABCYL reagents and related azo compounds.

• McCormack A¹
• Stephens J^1,2

•   ¹Department of Chemistry, Maynooth University, Maynooth W23 XY3X, Ireland
• ²The Kathleen Lonsdale Institute for Human Health Research, Maynooth University, Maynooth W23 XY3X, Ireland

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