Temperatures, filter cake release

Reaction times can be as short as 10 minutes in a continuous flow reactor (1). In a typical batch cycle, the slurry is heated to the reaction temperature and held for up to 24 hours, although hold times can be less than an hour for many processes. After reaction is complete, the material is cooled, either by batch cooling or by pumping the product slurry through a double-pipe heat exchanger. Once the temperature is reduced below approximately 100°C, the slurry can be released through a pressure letdown system to ambient pressure. The product is then recovered by filtration (qv). A series of wash steps may be required to remove any salts that are formed as by-products. The clean filter cake is then dried in a tray or tunnel dryer or reslurried with water and spray dried. 

A clean vessel was charged with water (20 gal), sodium hydrogen phosphate (25 kg, 183.5 mol), 5-(2-formyl-pyridin-2-yloxy)-benz[l,2,5]oxadiazole (15 kg, 62 mol), and Zert-butyl alcohol (99 gal). The mixture was stirred for 1 h, and then a solution of sodium chlorite (34 kg, 379 mol) in water (40 gal) was added at a rate to keep the internal temperature < 35 °C. The reaction was quenched with a solution of sodium bisulfite (90 kg) in water (99 gal) at a rate to keep the temperature < 25 °C. The tert-butyl alcohol was stripped at slightly below atmospheric temperature (to control the bisulfite fumes released) until the head temperature was 80 °C. After cooling to 20 °C, the solids were stirred for 5.5 h, filtered, and washed with water (10 gal). The wet cake was reslurried in water (30 gal) for 1 h at 80 °C. After cooling to 20-25 °C, the solids were slurried for 2 h, filtered, and washed with water (5 gal). The solids were dried in a vacuum oven at 45-55 °C until the KF was < 0.5%, yielding 14.3 kg (89%) of the desired product. 

---