| abstract |
A process for nitrating aromatic sulfonic acids using 30 to is describedn n n 80% nitric acid and nitric acid inhibitors in the absence of sulfuric acid, which is characterized in that aromatic sulfonic acid and nitric acid are combined in such a concentration that no nitration takes place, then the nitric acid concentration in the reaction mixture is increased by distilling off dilute nitric acid using a vacuum, nitration of the aromatic sulfonic acids takes place, the reaction mixture being continuously circulated through a falling film evaporator, the evaporator tubes of which are 5 to 50 ° C higher than the temperature of the reaction mixture, so that the increase in nitric acid concentration and nitration practically only take place in the falling film evaporator. |