Continuous indolyl-sodium prepn. from phenyl-glycine salt melt - by reacting with sodamide and alkali hydroxide melt in multiple screw extruder, used in prepn. of indigo

摘要

Continuous prepn. of indoxyl-Na, (I), comprises mixing a melt of an alkali metal salt of phenyl glycine with an Na amide/alkali hydroxide melt at 230-250 degrees C in a multiple worm extruder, whereby the melt in mixing- and reaction zone warms up to 260-340 degrees C. After reaction, the melt is discharged. Dwelling times in extruder, after mixing to reaction temp. is 0.5-3 min. The NH3 relased is drawn off in degassing zones. Use of multiple worm extruder allows good mixing of highly viscous melts. Surface of thin layers formed is constantly renewed. Heat released in exothermic reaction is drawn off quickly. No deposits are left in extruder. Process requires a smaller quantity of alkali hydroxide. Yield of (I), indigo quality and indigo yield are not affected.