Development of a Continuous Schotten–Baumann Route to an Acyl Sulfonamide

The development and scale-up of a synthetic route to tasisulam sodium (5-bromo-thiophene-2-sulfonic acid 2,4-dichlorobenzoylamide sodium salt, hereafter referred to as tasisulam) utilizing continuous Schotten–Baumann reaction conditions is disclosed. A new synthetic route for the cytotoxic API amenable to continuous processing was envisioned that would minimize potential worker exposure by reducing the number of unit operations and would allow commercial-scale API production in laboratory fume hoods with inexpensive glassware. The developed Schotten–Baumann conditions contained fewer unit operations than the existing batch process by utilizing the direct formation of the final sodium salt from a sulfonamide and acid chloride without isolation of the free acyl sulfonamide. Batch development, continuous proof of concept studies, 5.2 g/h lab-scale demonstration and 5 kg/day commercial-scale runs will be discussed. Very stringent release specifications were in place for the tasisulam API batch process, and the challenges of meeting these requirements for the continuous process are detailed. Finally, the quality of material generated during startup and shutdown transitions will be addressed.