反应详情

The process as claimed in claim 6, wherein, after the oxidation has ended the reaction mixture is subjected to a heat treatment at a temperature of between 90° and 120° C. under the autogenous pressure of 1 to 10 bar which is established, in the presence of sulfite, the resulting suspension of the tetrasodium salt of naphthalene-1,4,5,8-tetracarboxylic acid is cooled, after the reaction vessel has been let down, to a temperature of below 40° C. the pH is then adjusted to 4.5 to 5 by acidification, the resulting disodium salt of naphthalene-1,4,5,8-tetracarboxylic acid is isolated, this salt is converted into the tetrasodium salt of naphthalene-1,4,5,8-tetracarboxylic acid in an aqueous alkali metal hydroxide solution and, optionally after removal of insoluble impurities, naphthalene-1,4,5,8-tetracarboxylic acid 1,8-monoanhydride is precipitated by acidification to a pH of less than 2 at a temperature of 80° to 100° C.

1. customis subjected to a heat treatment at a temperature of between 90° and 120° C. under the autogenous pressure of 1 to 10 bar which
2. temperatureis cooled
3. customhas been let down, to a temperature of below 40° C.