PROCESS FOR THE NITRATION OF AROMATIC SULFONIC ACIDS

摘要

1. A process for nitrating aromatic sulfonic acids using 30 % to 80 % nitric acid and nitrous acid inhibitors, in the absence of sulfuric acid, characterized in that aromatic sulfonic acid and nitric acid are mixed in such a concentration that nitration does take place, then the concentration of the nitric acid in the reaction mixture is raised by distilling off dilute nitric acid in vacuo such that the aromatic sulfonic acid is nitrated, the reaction mixture being passed continuously in successive cycles through a falling film evaporator, the evaporator tubes of which have a temperature which is between 5 degrees and 50 degrees C higher than the temperature of the reaction mixture, so that the increase in the concentration of nitric acid and the nitration in effect take place only in the falling film evaporator.